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Quantitative Examination of Supra-Arcade Downflows in Eruptive Solar Flares      

David E McKenzie   Submitted: 2009-05-19 15:43

Downward motions above post-coronal mass ejection flare arcades are an unanticipated discovery of the Yohkoh mission, and have subsequently been detected with TRACE, SOHO/LASCO, SOHO/SUMER, and Hinode/XRT. These supra-arcade downflows are interpreted as outflows from magnetic reconnection, consistent with a three-dimensional generalization of the standard reconnection model of solar flares. We present results from our observational analyses of downflows, which include a semiautomated scheme for detection and measurement of speeds, sizes, and--for the first time--estimates of the magnetic flux associated with each shrinking flux tube. Though model dependent, these findings provide an empirical estimate of the magnetic flux participating in individual episodes of patchy magnetic ... [READ MORE]

Authors: D. E. McKenzie and Sabrina L. Savage
Projects: TRACE,Yohkoh-SXT

Publication Status: Accepted for publication in ApJ
Last Modified: 2009-05-20 09:24
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Distribution Functions of Sizes and Fluxes Determined from Supra-Arcade Downflows     

David E McKenzie   Submitted: 2011-06-22 14:58

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: D.E. McKenzie and S.L. Savage
Projects: Yohkoh-SXT

Publication Status: ApJL (published)
Last Modified: 2011-06-23 09:22
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Coronal loop oscillations observed with AIA : Kink-mode with cross-sectional and density oscillation     

Markus J. Aschwanden   Submitted: 2011-05-11 12:34

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Authors: Aschwanden,M.J. and Schrijver,C.J.
Projects: SDO-AIA

Publication Status: ApJ 736, 102-121, (2011)
Last Modified: 2011-08-08 15:37
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Predictions of Energy and Helicity in Four Major Eruptive Solar Flares     

Maria D Kazachenko   Submitted: 2011-07-21 12:14

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: Maria D. Kazachenko, Richard C. Canfield, Dana W. Longcope, Jiong Qiu
Projects: SoHO-MDI,TRACE

Publication Status: published in Solar Physics 07/2011
Last Modified: 2011-07-26 09:23
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Imaging Spectroscopy using AIA diffraction patterns in conjunction with RHESSI and EVE observations     

Claire Raftery   Submitted: 2011-11-17 16:29

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Authors: Claire L. Raftery, S?m Krucker, and Robert P. Lin
Projects: RHESSI,SDO-AIA,SDO-EVE

Publication Status: Accepted
Last Modified: 2011-11-18 09:30
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Investigation of the Formation and Separation of An EUV Wave from the Expansion of A Coronal Mass Ejection     

Xin Cheng   Submitted: 2011-12-19 18:17

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Authors: X. Cheng, J. Zhang, O. Olmedo, A. Vourlidas, M. D. Ding, and Y. Liu
Projects: SDO-AIA

Publication Status: accepted for publication in The Astrophysical Journal Letters
Last Modified: 2011-12-20 07:51
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Response of the Photospheric Magnetic Field to the X2.2 Flare on 2011 February 15     

Shuo Wang   Submitted: 2011-12-16 12:43

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Authors: Shuo Wang, Chang Liu, Rui Liu, Na Deng, Yang Liu, and Haimin Wang
Projects: Hinode/SOT,RHESSI,SDO-AIA,SDO-HMI

Publication Status: ApJ Letters, accepted
Last Modified: 2011-12-19 09:06
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First SDO/AIA Observation of Solar Prominence Formation Following an Eruption: Magnetic Dips and Sustained Condensation and Drainage     

Wei Liu   Submitted: 2012-01-04 11:43

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Authors: Wei Liu, Thomas E. Berger, and B. C. Low
Projects: SDO-AIA

Publication Status: ApJ Letters, Vol. 745, January 2012, in press
Last Modified: 2012-01-04 12:14
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Differential Emission Measures from the Regularized Inversion of Hinode and SDO data     

Iain Hannah   Submitted: 2012-01-23 11:24

We develop and apply an enhanced regularization algorithm, used in RHESSI X-ray spectral analysis, to constrain the ill-posed inverse problem that is determining the DEM from solar observations. We demonstrate this computationally fast technique applied to a range of DEM models simulating broadband imaging data from SDO/AIA and high resolution line spectra from Hinode/EIS, as well as actual active region observations with Hinode/EIS and XRT. As this regularization method naturally provides both vertical and horizontal (temperature resolution) error bars we are able to test the role of uncertainties in the data and response functions. The regularization method is able to successfully recover the DEM from simulated data of a variety of model DEMs (single Gaussian, multiple Gaussians and ... [READ MORE]

Authors: I. G. Hannah, E. P. Kontar
Projects: Hinode/EIS,Hinode/XRT,SDO-AIA,SDO-EVE

Publication Status: A&A (accepted)
Last Modified: 2012-01-24 11:24
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Center-to-Limb Variation of Radio Emissions from Thermal-Rich and Thermal-Poor Solar Flares     

Tomoko Kawate   Submitted: 2011-07-10 16:19

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Authors: T. Kawate, A. Asai, K. Ichimoto
Projects: Nobeyama Radioheliograph

Publication Status: PASJ (accepted)
Last Modified: 2011-07-12 11:14
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Hinode XRT observations of a long-lasting coronal sigmoid     

David E McKenzie   Submitted: 2009-05-19 16:04

Aims: Coronal sigmoids are important sources of eruptions into interplanetary space, and a handful of models have been proposed to explain their characteristic S shape. However, the coronal X-ray images available to date have generally not had sufficient resolution to distinguish between these models. The goal of the present investigation is to determine whether the new observations from Hinode can help us to make such a distinction. Methods: We present the first observations of a persistent coronal sigmoid obtained with the Hinode X-Ray Telescope (XRT). The excellent angular resolution of XRT (1 arcsec per pixel) and the sigmoid's location near disk center combined to provide an unprecedented view of the formation and eruption of this phenomenon. We compared the observed ... [READ MORE]

Authors: D. E. McKenzie and R. C. Canfield
Projects: Hinode/XRT

Publication Status: Published in Astronomy & Astrophysics (2008), v.481, L65-L68
Last Modified: 2009-05-20 09:24
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Rapid Changes of Photospheric Magnetic Field After Tether-cutting Reconnection and Magnetic Implosion     

Chang Liu   Submitted: 2011-12-13 14:20

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Authors: Chang Liu, Na Deng, Rui Liu, Jeongwoo Lee, Thomas Wiegelmann, Ju Jing, Yan Xu, Shuo Wang, and Haimin Wang
Projects: Hinode/SOT,RHESSI,SDO-AIA,SDO-HMI

Publication Status: ApJ Letters, accepted
Last Modified: 2011-12-13 14:37
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Sizes of flaring kernels in various parts of the H-alpha line profile     

Krzysztof Radziszewski   Submitted: 2008-05-08 04:14

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Authors: K. Radziszewski and P. Rudawy
Projects: MSDP Spectrograph (Wroclaw)

Publication Status: Published in Annales Geophysicae (Special Issue: SOHO 20 Solar Conference)
Last Modified: 2011-10-24 12:56
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Atomic data for the X-ray lines of Fe VIII & Fe IX     

Brendan O'Dwyer   Submitted: 2011-10-06 03:57

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Authors: O'Dwyer, B., Del Zanna, G., Badnell, N. R., Mason, H. E., Storey, P. J.
Projects: SDO-AIA

Publication Status: Accepted for publication in Astronomy and Astrophysics
Last Modified: 2011-10-06 11:40
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The 2011/02/15 X2 flare, ribbons, coronal wave, and mass ejection: interpreting the 3-d views from SDO and STEREO guided by MHD flux-rope modeling     

Karel Schrijver   Submitted: 2011-06-13 13:27

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Authors: C.J. Schrijver, G. Aulanier, A.M. Title, E. Pariat, C. Delannee
Projects: SDO-AIA,STEREO

Publication Status: ApJ, in press
Last Modified: 2011-06-14 19:51
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Coronal Fe XIV Emission During the Whole Heliosphere Interval Campaign     

Richard Altrock   Submitted: 2011-06-29 15:29

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Authors: Richard C. Altrock
Projects: National Solar Observatory (Sac Peak)

Publication Status: Solar Phys., Online First, Feb. 2011, DOI 10.1007/s11207-011-9714-9
Last Modified: 2011-06-30 06:51
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Using SDO's AIA to investigate energy transport from a flare's energy release site to the chromosphere     

Jeffrey W. Brosius   Submitted: 2011-12-14 14:02

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Authors: Brosius, J. W., & Holman, G. D.
Projects: RHESSI,SDO-AIA,SoHO-CDS

Publication Status: A&A (in press)
Last Modified: 2011-12-15 15:57
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Flare Physics in the Hinode Era (Keynote)     

David E McKenzie   Submitted: 2009-05-19 16:13

Hinode's manifest of instrumentation was conceived to investigate the magnetic connections through the photosphere, lower atmosphere, and corona. The complementarity of the instruments is indeed useful, as demonstrated in numerous flares and eruptions in just the first two years of operation. I will review some of the findings from Hinode's observations of flares to date. It is true, of course, that Hinode's capabilities have evolved since launch. These changes cause the planning of observations to be more complex, and the analysis to be less straightforward; but they do not diminish Hinode's ability to produce important observations of solar flares. On the contrary, Hinode is poised to make truly surprising discoveries. I will explain why this is so, and why we should look ... [READ MORE]

Authors: David E. McKenzie
Projects: Hinode/EIS,Hinode/SOT,Hinode/XRT

Publication Status: Accepted for publication in Hinode-2 proceedings.
Last Modified: 2009-05-20 09:24
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A Standard-to-Blowout Jet     

Chang Liu   Submitted: 2011-05-18 08:20

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Authors: Chang Liu, Na Deng, Rui Liu, Ignacio Ugarte-Urra, Shuo Wang, Haimin Wang
Projects: RHESSI,SDO-AIA,SDO-HMI

Publication Status: accepted to ApJL
Last Modified: 2011-05-18 10:40
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First Simultaneous Observation of H-alpha Moreton Wave, EUV Wave, and Filament/Prominence Oscillations     

Ayumi Asai   Submitted: 2011-12-27 00:40

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Authors: Asai, A., Ishii, T.T., Kitai R., Ichimoto, K., UeNo, S., Nagata, S., Morita, S., Nishida, K., Shiota, D., Oi, A., Akioka, M., Shibata, K.
Projects: SDO-AIA,STEREO

Publication Status: accepted by ApJL
Last Modified: 2011-12-28 12:07
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LYRA observations of two oscillation modes in a single flare     

Tom Van Doorsselaere   Submitted: 2011-08-23 06:43

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Authors: Van Doorsselaere T., De Groof A., Zender J., Berghmans D., and Goossens M.
Projects: Hinode/XRT, PROBA2/LYRA

Publication Status: ApJ (accepted)
Last Modified: 2011-08-23 08:55
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3D Reconstructions of an Erupting Filament with SDO and STEREO Observations     

Ting Li   Submitted: 2011-07-06 02:58

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Authors: Ting Li, Jun Zhang, Yuzong Zhang, Shuhong Yang
Projects: SDO-AIA,SDO-HMI,SoHO-MDI,STEREO

Publication Status: ApJ; accepted
Last Modified: 2011-07-06 09:16
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Observation of High-speed Outflow on Plume-like Structures of the Quiet Sun and Coronal Holes with SDO/AIA     

Hui Tian   Submitted: 2011-05-17 14:55

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Authors: Hui Tian, Scott W. McIntosh, Shadia Rifal Habbal, Jiansen He
Projects: Hinode/EIS,SDO-AIA,STEREO

Publication Status: ApJ, in press
Last Modified: 2011-05-17 19:26
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Plasma diagnostic in eruptive prominences from SDO/AIA observations at 304     

Nicolas Labrosse   Submitted: 2011-11-21 05:17

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Authors: Labrosse N. & McGlinchey K.
Projects: SDO-AIA

Publication Status: Accepted, A&A
Last Modified: 2011-11-22 03:20
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Ubiquitous rotating network magnetic fields and EUV cyclones in the quiet Sun     

Shuhong Yang   Submitted: 2011-09-22 22:47

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Authors: Jun Zhang and Yang Liu
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2011-09-25 05:08
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Quasi periodic oscillations of solar active regions in connection with their flare activity - NoRH observations     

Vladimir Abramov-Maximov   Submitted: 2011-07-11 16:24

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Authors: Vladimir Abramov-Maximov, George Gelfreikh, Kiyoto Shibasaki
Projects: Nobeyama Radioheliograph

Publication Status: Solar Physics, Volume 273, Number 2, pp.403-412, DOI: 10.1007/s11207-011-9822-6
Last Modified: 2011-11-17 09:28
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Solar Torsional Oscillations and Their Relationship to Coronal Activity     

Richard Altrock   Submitted: 2007-10-12 15:13

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Authors: Richard Altrock, Rachel Howe and Roger Ulrich
Projects: GONG,National Solar Observatory (Sac Peak)

Publication Status: ASP Conference Proceedings, vol.383, pp. 335-342, 2008, Proceedings of the 24th NSO Workshop, Subsurface and Atmospheric Influences on Solar Activity
Last Modified: 2012-01-11 14:26
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A new look at a polar crown cavity as observed by SDO/AIA     

Stephane Regnier   Submitted: 2011-07-18 08:03

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Authors: S. Regnier, R. W. Walsh, C. E. Alexander
Projects: SDO-AIA

Publication Status: Accepted for publication in A&A
Last Modified: 2011-07-18 10:58
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Tracking a Ulysses high-latitude ICME event back to its solar origins     

Cristiana Dumitrache   Submitted: 2011-08-30 07:12

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Authors: Dumitrache,C; Popescu, N.A.; Oncica, A.
Projects: SoHO-LASCO

Publication Status: Solar Physics 272, 137-157, DOI: 10.1007/s11207-011-9811-9, 2011
Last Modified: 2011-08-30 10:49
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The Strength and Radial Profile of Coronal Magnetic Field from the Standoff Distance of a CME-driven Shock     

Nat Gopalswamy   Submitted: 2011-06-29 16:55

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Authors: N. Galswamy and S. Yashiro
Projects: SoHO-LASCO,STEREO

Publication Status: To be published online on Wednesday, June 29. It will appear in print in the July 20, 2011 issue (736/1)
Last Modified: 2011-06-30 06:51
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Isothermal and Multithermal Analysis of Coronal Loops Observed with AIA: II. 211 A Selected Loops     

Joan Schmelz   Submitted: 2011-07-08 10:41

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Authors: J.T. Schmelz, B.T. Worley, D.J. Anderson , S. Pathak, J.A. Kimble, B.S. Jenkins, S.H. Saar
Projects: SDO-AIA

Publication Status: ApJ (in press)
Last Modified: 2011-07-08 11:23
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SDO AIA and Hinode EIS observations of `warm' loops     

Giulio Del Zanna   Submitted: 2011-09-08 06:38

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Authors: Del Zanna, G, O' Dwyer, B., Mason, H.E.
Projects: Hinode/EIS,SDO-AIA

Publication Status: A&A, accepted
Last Modified: 2011-09-08 09:32
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Height structure of X-ray, EUV and white-light emission in a solar flare     

Marina Battaglia   Submitted: 2011-07-21 03:56

Context. The bulk of solar flare emission originates from very compact sources located in the lower solar atmosphere and observable at a broad range of wavelengths such as near optical, UV, EUV, soft and hard X-rays, and gamma-rays. Nevertheless, very few spatially resolved imaging observations have been performed to determine the structure of these compact regions.
Aims: We investigate the above-the-photosphere heights of hard X-ray (HXR), EUV, and white-light (6173 Å) continuum sources in the low atmosphere and the corresponding densities at these heights. By considering the collisional transport of solar energetic electrons, we also determine where and how much energy is deposited and compare these values with the emissions observed in HXR, EUV, and the continuum.
... [READ MORE]

Authors: Marina Battaglia, Eduard P. Kontar
Projects: RHESSI,SDO-AIA,SDO-HMI

Publication Status: Astronomy & Astrophysics Letters, accepted
Last Modified: 2011-07-21 08:42
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Plasmoid Releases in the Heliospheric Current Sheet and Associated Coronal Hole Boundary Layer Evolution     

Claire Foullon   Submitted: 2011-05-17 12:13

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Authors: Foullon, C., Lavraud, B., Luhmann, J.G., Farrugia, C.J., Retinò, A., Simunac, K.D.C., Wardle, N.C., Galvin, A.B., Kucharek, H., Owen, C.J., Popecki, M., Opitz, A. and Sauvaud, J.-A.
Projects: SoHO-LASCO,STEREO

Publication Status: ApJ (in press)
Last Modified: 2011-05-17 19:26
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Anatomy of a solar flare: measurements of the December 14, 2006 X-class flare with GONG, Hinode and RHESSI     

Sarah Matthews   Submitted: 2011-07-12 09:48

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Authors: Sarah Matthews, Sergei Zharkov & Valentina Zharkova
Projects: Hinode/SOT,TRACE,RHESSI,GONG

Publication Status: ApJ, In press
Last Modified: 2011-07-12 11:14
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SDO/AIA Observations of Secondary Waves Generated by Interaction of the 2011 June 7 Global EUV Wave With Solar Coronal Structures     

Ting Li   Submitted: 2011-11-08 08:38

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Authors: Ting Li, Jun Zhang, Shuhong Yang, Wei Liu
Projects: SDO-AIA,STEREO

Publication Status: accepted for publication in ApJ
Last Modified: 2011-11-08 09:00
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The Wave Properties of Coronal Bright Fronts Observed Using SDO/AIA     

David Long   Submitted: 2011-09-27 04:06

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Authors: Long, David M., DeLuca, Edward E., Gallagher, Peter T.
Projects: SDO-AIA,STEREO

Publication Status: ApJL (in press)
Last Modified: 2011-09-27 10:19
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Evolution of Magnetic Field and Energy in A Major Eruptive Active Region Based on SDO/HMI Observation     

Xudong Sun   Submitted: 2012-01-16 14:12

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Authors: Xudong Sun, J. Todd Hoeksema, Yang Liu, Thomas Wiegelmann, Keiji Hayashi, Qingrong Chen, Julia Thalmann
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted by ApJ
Last Modified: 2012-01-16 21:07
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Spatially resolved observations of a split-band coronal type-II radio burst    

Ivan Zimovets   Submitted: 2012-08-28 02:59

Context. The origin of coronal type-II radio bursts and of their band-splitting are still not fully understood. Aims. To make progress in solving this problem on the basis of one extremely well observed solar eruptive event. Methods. The relative dynamics of multi-thermal eruptive plasmas, observed in detail by the SDO/AIA and of the harmonic type-II burst sources, observed by the NRH at ten frequencies from 445 to 151 MHz, is studied for the partially behind the limb event on 3 November 2010. Special attention is given to the band-splitting of the burst. Analysis is supplemented by investigation of coronal hard X-ray (HXR) sources observed by the RHESSI. Results. It is found that the flare impulsive phase was accompanied by the formation of a double coronal HXR source, whose ... [READ MORE]

Authors: I. Zimovets, N. Vilmer, A. C.-L. Chian, I. Sharykin, A. Struminsky
Projects: Nan?ay Radioheliograph,RHESSI,SDO-AIA

Publication Status: A&A (accepted)
Last Modified: 2012-08-28 12:33
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Enhancement of a sunspot light wall with external disturbances    

Shuhong Yang   Submitted: 2016-11-30 21:39

Based on the Interface Region Imaging Spectrograph observations, we study the response of a solar sunspot light wall to external disturbances. A flare occurrence near the light wall caused material to erupt from the lower solar atmosphere into the corona. Some material falls back to the solar surface, and hits the light bridge (i.e., the base of the light wall), then sudden brightenings appear at the wall base followed by the rise of wall top, leading to an increase of the wall height. Once the brightness of the wall base fades, the height of the light wall begins to decrease. Five hours later, another nearby flare takes place, a bright channel is formed that extends from the flare towards the light bridge. Although no obvious material flow along the bright channel is found, some ejected ... [READ MORE]

Authors: Shuhong Yang, Jun Zhang, Robert Erd?lyi
Projects: IRIS,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2016-12-14 13:55
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Off-limb (spicule) DEM distribution from SoHO/SUMER observations    

Kamalam Vanninathan   Submitted: 2012-03-28 08:23

In the present work we derive a Differential Emission Measure (DEM) distribution from a region dominated by spicules. We use spectral data from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on-board the Solar Heliospheric Observatory (SoHO) covering the entire SUMER wavelength range taken off-limb in the Northern polar coronal hole to construct this DEM distribution using the CHIANTI atomic database. This distribution is then used to study the thermal properties of the emission contributing to the 171 A channel in the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO). From our off-limb DEM we found that the radiance in the AIA 171 A channel is dominated by emission from the Fe IX 171.07 A line and has sparingly little ... [READ MORE]

Authors: K. Vanninathan, M. S. Madjarska, E. Scullion, J. G. Doyle
Projects: SDO-AIA,SoHO-SUMER

Publication Status: accepted for publication in Solar Physics
Last Modified: 2012-03-28 12:44
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Production of the Extreme-Ultraviolet Late Phase of an X Class Flare in a Three-Stage Magnetic Reconnection Process    

Yu Dai   Submitted: 2013-07-18 19:21

We report observations of an X class flare on 2011 September 6 by the instruments onboard the Solar Dynamics Observatory (SDO). The flare occurs in a complex active region with multiple polarities. The Extreme-Ultraviolet (EUV) Variability Experiment (EVE) observations in the warm coronal emission reveal three enhancements, of which the third one corresponds to an EUV late phase. The three enhancements have a one-to-one correspondence to the three stages in flare evolution identified by the spatially-resolved Atmospheric Imaging Assembly (AIA) observations, which are characterized by a flux rope eruption, a moderate filament ejection, and the appearance of EUV late phase loops, respectively. The EUV late phase loops are spatially and morphologically distinct from the main flare loops. ... [READ MORE]

Authors: Y. Dai, M. D. DIng, Y. Guo
Projects: SDO-AIA

Publication Status: ApJ Letters (in press)
Last Modified: 2013-07-19 10:35
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A Simple Way to Estimate the Soft X-ray Class of Far-Side Solar Flares Observed with STEREO/EUVI    

Ilya Chertok   Submitted: 2015-05-08 00:32

Around the peaks of substantial flares, bright artifact nearly horizontal saturation streaks (B-streaks) corresponding to the brightest parts of the flare sources appear in the STEREO/EUVI 195 ? images. We show that the length of such B-streaks can be used for the solution of an actual problem of evaluating the soft X-ray flux and class of far-side flares registered with double STEREO spacecraft but invisible from Earth. For this purpose from data on about 350 flares observed from January 2007 to July 2014 (mainly exceeding the GOES M1.0 level) both with GOES and STEREO, an empirical relation is established correlating the GOES 1-8 ? peak flux and the B-streak length. This allowed us for the same years to estimate the soft X-ray classes for approximately 65 strong far-side flares observed ... [READ MORE]

Authors: Chertok, I. M., Belov, A. V., Grechnev, V. V.
Projects: GOES X-rays ,STEREO

Publication Status: Solar Physics, submitted
Last Modified: 2015-05-12 14:02
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Geoeffectiveness of halo coronal mass ejections    

Nat Gopalswamy   Submitted: 2007-02-10 05:21

We studied the geoeffectiveness, speed, solar source, and flare association of a set of 378 halo coronal mass ejections (CMEs) of cycle 23 (1996-2005, inclusive). We compiled the minimum Dst values occurring within 1-5 days after the CME onset. We compared the distributions of such Dst values for the following subsets of halo CMEs: disk halos (within 45 deg from disk center), limb halos (beyond 45 degrees but within 90 deg from disk center), and backside halo CMEs. On the average, the disk halos are followed by intense storms, limb halos are followed by moderate storms, and backside halos are not followed by significant storms. The Dst distribution for a random sample is nearly identical to the case of backside halos. We found that ~71% of all frontside halos are geoeffective, supporting ... [READ MORE]

Authors: N. Gopalswamy, S. Yashiro, and S. Akiyama
Projects: SoHO-LASCO

Publication Status: JGR accepted Feb 7, 2007
Last Modified: 2007-02-10 08:29
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Coronal Magnetic Field Evolution from 1996 to 2012: Continuous Non-Potential Simulations    

Anthony Yeates   Submitted: 2013-04-03 02:20

Coupled flux transport and magneto-frictional simulations are extended to simulate the continuous magnetic field evolution in the global solar corona for over 15 years, from the start of Solar Cycle 23 in 1996. By simplifying the dynamics, our model follows the build-up and transport of electric currents and free magnetic energy in the corona, offering an insight into the magnetic structure and topology that extrapolation-based models can not. To enable these extended simulations, we have implemented a more efficient numerical grid, and have carefully calibrated the surface flux transport model to reproduce the observed large-scale photospheric radial magnetic field, using emerging active regions determined from observed line-of-sight magnetograms. This calibration is described in some ... [READ MORE]

Authors: A. R. Yeates
Projects: Other,SoHO-LASCO

Publication Status: Solar Physics (in press)
Last Modified: 2013-04-03 12:09
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Shock Connectivity in the August 2010 and July 2012 Solar Energetic Particle Events Inferred from Observations and ENLIL Modeling    

Hazel Bain   Submitted: 2016-06-28 13:36

During periods of increased solar activity, coronal mass ejections (CMEs) can occur in close succession and proximity to one another. This can lead to the interaction and merger of CME ejecta as they propagate in the heliosphere. The particles accelerated in these shocks can result in complex solar energetic particle (SEP) events, as observing spacecraft form both remote and local shock connections. It can be challenging to understand these complex SEP events from in situ profiles alone. Multipoint observations of CMEs in the near-Sun environment, from the Solar Terrestrial Relations Observatory-Sun Earth Connection Coronal and Heliospheric Investigation and the Solar and Heliospheric Observatory Large Angle and Spectrometric Coronagraph, greatly improve our chances of ... [READ MORE]

Authors: H. M. Bain, M. L. Mays, J. G. Luhmann, Y. Li, L. K. Jian, and D. Odstrcil
Projects: ACE,SoHO-LASCO,STEREO

Publication Status: Published
Last Modified: 2016-06-29 13:47
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Frequency drifts of 3-min oscillations in microwave and EUV emission above sunspots    

Robert Sych   Submitted: 2011-11-02 19:19

We analyse 3-min oscillations of microwave and EUV emission generated at different heights of a sunspot atmosphere, studying the amplitude and frequency modulation of the oscillations, and its relationship with the variation of the spatial structure of the oscillations. High-resolution data obtained with the Nobeyama Radioheliograph, TRACE and SDO/AIA are analysed with the use of the Pixelised Wavelet Filtering and wavelet skeleton techniques. 3-min oscillations in sunspots appear in the form of repetitive trains of the duration 8-20 min (13 min in average). The typical interval between the trains is 30-50 min. The oscillation trains are transient in frequency and power. We detected a repetitive frequency drifts of 3-min oscillations during the development of individual trains. Wavelet ... [READ MORE]

Authors: R. Sych, T. V. Zaqarashvili, V. M. Nakariakov, S.A. Anfinogentov, K.Shibasaki and Y. Yan
Projects: Nobeyama Radioheliograph,SDO-AIA,TRACE

Publication Status: A&A (in press), 2011
Last Modified: 2011-11-03 15:21
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Period persistence of long period oscillations in sunspots    

Nicky Chorley   Submitted: 2011-04-06 04:12

Long period oscillations in the microwave radiation intensity generated over the sunspot of NOAA AR 10330 are studied with the Nobeyama Radioheliograph as the sunspot passes over the solar disk, over the course of 9 days (06−15 April 2003). Periodogram, Fourier and global wavelet analyses reveal the presence of a significant oscillatory component in the range P ≈  50−120 min over the course of the observations. The spectral amplitudes of five significant Fourier components in the range P = 50−150 min are also seen to be stable over the observations, when the data are not affected by changes in magnetic configuration in the region. The ground-based nature of the instrument naturally introduces long data gaps in such long ... [READ MORE]


Authors: N. Chorley, C. Foullon, B. Hnat, V. M. Nakariakov & K. Shibasaki
Projects: Nobeyama Radioheliograph

Publication Status: A&A, 529, A123.
Last Modified: 2011-04-15 08:06
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First magnetic seismology of the CME reconnection outflow layer in the low corona with 2.5-D MHD simulations of the Kelvin-Helmholtz instability    

Claire Foullon   Submitted: 2013-09-26 10:41

For conditions observed in the low corona, we perform 2.5-D magnetohydrodynamic (MHD) simulations of the Kelvin-Helmholtz instability (KHI) at the surface of a coronal mass ejection (CME). We match the observed time development of the KHI with simulated growth from 110 MHD experiments representing a parametric range of realistic magnetic field strengths and orientations and two key values of the velocity shear, ΔV, inferred from observations. The results are field strengths Be≈ 8?9 G and Bs≈ 10?11 G in the CME reconnection outflow layer and the surrounding sheath, respectively, for ΔV≈770kms−1; for nearly perpendicular orientation (1? tilt) of Bs with respect to the flow plane, Be can be tilted between 3 and 10?; tilting Bs up to 15? would slow the growth ... [READ MORE]

Authors: Nykyri, K. and Foullon, C.
Projects: SDO-AIA

Publication Status: Geophysical Research Letters Vol. 40 (16), pp. 4154 ? 4159
Last Modified: 2013-09-30 10:00
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Three-dimensional Density Structure of a Solar Coronal Streamer Observed by SOHO/LASCO and STEREO/COR2 in Quadrature    

Bieke Decraemer   Submitted: 2019-08-20 08:30

Helmet streamers are a prominent manifestation of magnetic structures with current sheets in the solar corona. These large-scale structures are regions with high plasma density, overlying active regions and lament channels. We investigate the three-dimensional (3D) structure of a coronal streamer, observed simultaneously by white-light coronagraphs from two vantage points near quadrature (SOHO/LASCO and STEREO/COR2). We design a forward model based on plausible assumptions about the 3D streamer structure taken from physical models (a plasma slab centered around a current sheet). The streamer stalk is approximated by a plasma slab, with electron density that is characterized by three separate functions describing the radial, transverse and face-on pro les respectively. For the ... [READ MORE]

Authors: Bieke Decraemer, Andrei N. Zhukov, and Tom Van Doorsselaere
Projects: SoHO-LASCO,STEREO

Publication Status: Accepted for publication in The Astrophysical Journal
Last Modified: 2019-08-21 14:20
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Formation and Eruption of an Active Region Sigmoid: I. Study by Nonlinear Force-Free Field Modeling    

Chaowei Jiang   Submitted: 2013-10-30 20:55

We present a magnetic analysis of the formation and eruption of an active region (AR) sigmoid in AR 11283 from 2011 September 4 to 6. To follow the quasi-static evolution of the coronal magnetic field, we reconstruct a time sequence of static fields using a recently developed nonlinear force-free field model constrained by the SDO/HMI vector magnetograms. A detailed analysis of the fields compared with the SDO/AIA observations suggests the following scenario for the evolution of the region. Initially, a new bipole emerges into the negative polarity of a pre-existing bipolar AR, forming a null point topology between the two flux systems. A weakly twisted flux rope (FR) is then built up slowly in the embedded core region, largely through flux-cancellation photospheric reconnections, forming ... [READ MORE]

Authors: Chaowei Jiang, S. T. Wu, Xueshang Feng, Qiang Hu
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted by ApJ
Last Modified: 2013-10-31 08:18
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Anti-parallel EUV flows observed along active region filament threads with Hi-C    

Caroline Alexander   Submitted: 2013-06-24 07:25

Plasma flows within prominences/filaments have been observed for many years and hold valuable clues concerning the mass and energy balance within these structures. Previous observations of these flows primarily come from H-alpha and cool EUV lines (e.g., 304A) where estimates of the size of the prominence threads has been limited by the resolution of the available instrumentation. Evidence of `counter-steaming' flows has previously been inferred from these cool plasma observations but now, for the first time, these flows have been directly imaged along fundamental filament threads within the million degree corona (at 193A). In this work we present observations of an active region filament observed with Hi-C that exhibits anti-parallel flows along adjacent filament threads. Complementary ... [READ MORE]

Authors: Caroline E. Alexander, Robert W. Walsh, Stephane Regnier, Jonathan Cirtain, Amy R. Winebarger, Leon Golub, Ken Kobayashi, Simon Platt, Nick Mitchell, Kelly Korreck, Bart DePontieu, Craig DeForest, Mark Weber, Alan Title, Sergey Kuzin
Projects: Other,SDO-AIA

Publication Status: Published in ApJ, 775, L32
Last Modified: 2013-09-13 09:55
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Quasi-periodic Fast-mode Wave Trains Within a Global EUV Wave and Sequential Transverse Oscillations Detected by SDO/AIA    

Wei Liu   Submitted: 2012-04-25 09:50

We present the first unambiguous detection of quasi-periodic wave trains within the broad pulse of a global EUV wave (so-called ''EIT wave'') occurring on the limb. These wave trains, running ahead of the lateral CME front of 2-4 times slower, coherently travel to distances $>R_{sun}/2$ along the solar surface, with initial velocities up to 1400 km/s decelerating to ~650 km/s. The rapid expansion of the CME initiated at an elevated height of 110 Mm produces a strong downward and lateral compression, which may play an important role in driving the primary EUV wave and shaping its front forwardly inclined toward the solar surface. The waves have a dominant 2 min periodicity that matches the X-ray flare pulsations, suggesting a causal connection. The arrival of the leading EUV wave front at ... [READ MORE]

Authors: Wei Liu, Leon Ofman, Nariaki V. Nitta, Markus J. Aschwanden, Carolus J. Schrijver, Alan M. Title, and Theodore D. Tarbell
Projects: SDO-AIA

Publication Status: Accepted by ApJ, Apr 24, 2012
Last Modified: 2012-04-25 12:18
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Quasi-periodic Fast-mode Magnetosonic Wave Trains Within Coronal Waveguides Associated with Flares and CMEs    

Wei Liu   Submitted: 2015-12-22 22:42

Quasi-periodic, fast-mode, propagating wave trains (QFPs) are a new observational phenomenon recently discovered in the solar corona by the Solar Dynamics Observatory with extreme ultraviolet (EUV) imaging observations. They originate from flares and propagate at speeds up to ~2000 km/s within funnel-shaped waveguides in the wakes of coronal mass ejections (CMEs). QFPs can carry sufficient energy fluxes required for coronal heating during their occurrences. They can provide new diagnostics for the solar corona and their associated flares. We present recent observations of QFPs focusing on their spatio-temporal properties, temperature dependence, and statistical correlation with flares and CMEs. Of particular interest is the 2010-Aug-01 C3.2 flare with correlated QFPs and drifting zebra ... [READ MORE]

Authors: Wei Liu, Leon Ofman, Brittany Broder, Marian Karlicky, and Cooper Downs
Projects: IRIS,RHESSI,SDO-AIA

Publication Status: Accepted to the Proceedings of the 14th International Solar Wind Conference
Last Modified: 2015-12-23 12:23
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Global Energetics of Solar Flares: IV. Coronal Mass Ejection Energetics    

Markus J. Aschwanden   Submitted: 2016-05-16 14:50

This study entails the fourth part of a global flare energetics project, in which the mass mcme, kinetic energy Ekin, and the gravitational potential energy Egrav of coronal mass ejections (CMEs) is measured in 399 M and X-class flare events observed during the first 3.5 yrs of the Solar Dynamics Observatory (SDO) mission, using a new method based on the EUV dimming effect. The EUV dimming is modeled in terms of a radial adiabatic expansion process, which is fitted to the observed evolution of the total emission measure of the CME source region. The model derives the evolution of the mean electron density, the emission measure, the bulk plasma expansion velocity, the mass, and the energy in the CME source region. The EUV ... [READ MORE]

Authors: Aschwanden, M.J.
Projects: SDO-AIA

Publication Status: ApJ, subm. 2016 May 16
Last Modified: 2016-05-16 20:09
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Quadrature Observations of Wave and Non-Wave Components and Their Decoupling in an Extreme-Ultraviolet Wave Event    

Yu Dai   Submitted: 2012-08-28 00:35

We report quadrature observations of an extreme-ultraviolet (EUV) wave event on 2011 January 27 obtained by the Extreme Ultraviolet Imager (EUVI) onboard emph{Solar Terrestrial Relations Observatory} (emph{STEREO}), and the Atmospheric Imaging Assembly (AIA) onboard the emph{Solar Dynamics Observatory} (emph{SDO}). Two components are revealed in the EUV wave event. A primary front is launched with an initial speed of $sim$440 km s$^{-1}$. It appears significant emission enhancement in the hotter channel but deep emission reduction in the cooler channel. When the primary front encounters a large coronal loop system and slows down, a secondary much fainter front emanates from the primary front with a relatively higher starting speed of $sim$550 km s$^{-1}$. Afterwards the two fronts ... [READ MORE]

Authors: Y. Dai, M. D. Ding, P. F. Chen, J. Zhang
Projects: SDO-AIA

Publication Status: Accepted for publication in ApJ
Last Modified: 2012-08-28 12:30
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Measuring the magnetic field of a trans-equatorial loop system using coronal seismology    

David Long   Submitted: 2017-04-04 01:00

"EIT waves" are freely-propagating global pulses in the low corona which are strongly associated with the initial evolution of coronal mass ejections (CMEs). They are thought to be large-amplitude, fast-mode magnetohydrodynamic waves initially driven by the rapid expansion of a CME in the low corona. An "EIT wave" was observed on 6 July 2012 to impact an adjacent trans-equatorial loop system which then exhibited a decaying oscillation as it returned to rest. Observations of the loop oscillations were used to estimate the magnetic field strength of the loop system by studying the decaying oscillation of the loop, measuring the propagation of ubiquitous transverse waves in the loop and extrapolating the magnetic field from observed magnetograms. Observations from the Atmospheric Imaging ... [READ MORE]

Authors: David M. Long, Gherardo Valori, David P?rez-Su?rez, Richard J. Morton, Alberto Marcos V?squez
Projects: MLSO/CoMP,SDO-AIA

Publication Status: Accepted for publication in A&A
Last Modified: 2017-04-04 08:09
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A statistical study of the post-impulsive-phase acceleration of flare-associated coronal mass ejections    

Xin Cheng   Submitted: 2010-02-26 04:19

It is now generally accepted that the impulsive acceleration of a coronal mass ejection (CME) in the inner corona is closely correlated in time with the main energy release of the associated solar flare. In this paper, we examine in detail the post-impulsive-phase acceleration of a CME in the outer corona, which is the phase of evolution immediately following the main impulsive acceleration of the CME; this phase is believed to correspond to the decay phase of the associated flare. This observational study is based on a statistical sample of 247 CMEs that are associated with M- and X-class GOES soft X-ray flares from 1996 to 2006. We find that, from many examples of events, the CMEs associated with flares with long-decay time (or so-called long-duration flares) tend to have positive ... [READ MORE]

Authors: X. Cheng, J. Zhang, M. D. Ding, W. Poomvises
Projects: SoHO-LASCO

Publication Status: ApJ (in press)
Last Modified: 2010-02-26 18:53
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On the nature of prominence emission observed by SDO/AIA    

Susanna Parenti   Submitted: 2012-05-25 00:53

The Prominence-Corona Transition Region (PCTR) plays a key role in the thermal and pressure equilibrium of solar prominences. Our knowledge of this interface is limited and several major issues remain open, including the thermal structure and, in particular, the maximum temperature of the detectable plasma. The high signal-to-noise ratio of images obtained by the Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory clearly show that prominences are often seen in emission in the 171 and 131 bands. We investigate the temperature sensitivity of these AIA bands for prominence observation, in order to infer the temperature content in an effort to explain the emission. Using the CHIANTI atomic database and previously determined prominence differential emission measure ... [READ MORE]

Authors: Susanna Parenti, Brigitte Schmieder, Petr Heinzel, Leon Golub
Projects: SDO-AIA

Publication Status: accepted on ApJ
Last Modified: 2012-05-25 11:39
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A quasi-periodic fast-propagating magnetosonic wave associated with the eruption of a magnetic flux rope    

Yuandeng Shen   Submitted: 2017-12-27 18:19

Using high temporal and high spatial resolution observations taken by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, we present the detailed observational analysis of a high quality quasi-periodic fast- propagating (QFP) magnetosonic wave that was associated with the eruption of a magnetic flux rope and a GOES C5.0 flare. For the first time, we find that the QFP wave lasted during the entire flare lifetime rather than only the rising phase of the accompanying flare as reported in previous studies. In addition, the propagation of the different parts of the wave train showed different kinematics and morphologies. For the southern (northern) part, the speed, duration, intensity variation are about 875 +/- 29 (1485 +/- 233) km/s, 45 (60) minutes, and 4% (2%), and the ... [READ MORE]

Authors: Yuandeng Shen; Yu Liu; Tengfei Song; Zhanjun Tian
Projects: SDO-AIA

Publication Status: accept for publication in ApJ
Last Modified: 2018-01-03 11:40
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Multiwavelength Analysis of a Solar Flare on 2002 April 15    

Linhui Sui   Submitted: 2005-09-30 08:28

We carried out a multiwavelength analysis of the solar limb flare on 2002 April 15. The observations all indicate that the flare occurred in an active region with an asymmetric dipole magnetic configuration. The earlier conclusion that magnetic reconnection is occurring in a large-scale current sheet in this flare is further supported by these observations: (1) Several blob-like sources, seen in RHESSI 12-25 keV X-ray images later in the flare, appeared along a line above the flare loops. These indicate the continued presence of the current sheet and are likely to be magnetic islands in the stretched sheet produced by the tearing-mode instability. (2) A cusp-like structure is seen in NoRH 34 GHz microwave images around the time of the peak flare emission. We quantitatively demonstrate ... [READ MORE]

Authors: Sui, L, Holman, G. D., White, S. M., Zhang, J.
Projects: RHESSI,Soho-MDI,Soho-LASCO,TRACE

Publication Status: ApJ, in press (Issue of Novermber 10)
Last Modified: 2005-09-30 08:28
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Multiwavelength Observations of a Slow Raise, Multi-Step X1.6 Flare and the Associated Eruption    

Vasyl Yurchyshyn   Submitted: 2015-09-21 11:30

Using multi-wavelength observations we studied a slow rise, multi-step X1.6 flare that began on November 7, 2014 as a localized eruption of core fields inside a $\delta$-sunspot and later engulfed the entire active region. This flare event was associated with formation of two systems of post eruption arcades and several J-shaped flare ribbons showing extremely fine details, irreversible changes in the photospheric magnetic fields, and it was accompanied by a fast and wide coronal mass ejection. Data from the Solar Dynamics Observatory, IRIS spacecraft along with the ground based data from the New Solar Telescope (NST) present evidence that i) the flare and the eruption were directly triggered by a flux emergence that occurred inside a $\delta$--sunspot at the boundary between two umbrae; ... [READ MORE]

Authors: Yurchyshyn, V., Kumar, P., Cho, K.S., Lim, E.K., & Abramenko, V.
Projects: IRIS,SDO-AIA,SDO-HMI

Publication Status: ApJ., accepted
Last Modified: 2015-09-23 13:32
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Ultra-narrow Negative Flare Front Observed in Helium-10830~\AA\ using the 1.6 m New Solar Telescope    

Yan Xu   Submitted: 2016-01-21 17:20

Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles which have adverse effects in the near Earth environment. By definition, flares are usually referred to bright features resulting from excess emission. Using the newly commissioned 1.6~m New Solar Telescope at Big Bear Solar Observatory, here we show a striking ``negative'' flare with a narrow, but unambiguous ``dark'' moving front observed in \ion{He}{1} 10830~\AA, which is as narrow as 340 km and is associated with distinct spectral characteristics in H$\alpha$ and \ion{Mg}{2} lines. Theoretically, such negative contrast in \ion{He}{1} 10830~\AA\ can be produced under special circumstances, by nonthermal-electron collisions, or photoionization ... [READ MORE]

Authors: Yan Xu, Wenda Cao, Mingde Ding, Lucia Kleint, Jiangtao Su, Chang Liu, Haisheng Ji, Jongchul Chae, Ju Jing, Kyuhyoun Cho, Kyungsuk Cho, Dale Gary, and Haimin Wang
Projects: IRIS,Other,SDO-AIA,SDO-HMI

Publication Status: accepted by ApJ
Last Modified: 2016-01-26 21:32
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Exploring the biases of a new method based on minimum variance for interplanetary magnetic clouds    

Pascal Demoulin   Submitted: 2018-09-03 04:12

Magnetic clouds (MCs) are twisted magnetic structures ejected from the Sun and probed by in situ instruments. They are typically modeled as flux ropes (FRs). The determination of the FR global characteristics requires the estimation of the FR axis orientation. Among the developed methods, the minimum variance (MV) is the most flexible, and features only a few assumptions. However, as other methods, MV has biases. We aim to investigate the limits of the method and extend it to a less biased method. We first identified the origin of the biases by testing the MV method on cylindrical and elliptical models with a temporal expansion comparable to the one observed in MCs. Then, we developed an improved MV method to reduce these biases. In contrast with many previous publications we find ... [READ MORE]

Authors: Pascal D?moulin, Sergio Dasso, Miho Janvier
Projects: ACE

Publication Status: A&A, in press
Last Modified: 2018-09-04 09:19
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An Observationally-Constrained Model of a Flux Rope that Formed in the Solar Corona    

Alexander James   Submitted: 2018-02-27 09:22

Coronal mass ejections (CMEs) are large-scale eruptions of plasma from the coronae of stars. Understanding the plasma processes involved in CME initiation has applications to space weather forecasting and laboratory plasma experiments. James et al. (Sol. Phys. 292, 71, 2017) used EUV observations to conclude that a magnetic flux rope formed in the solar corona above NOAA Active Region 11504 before it erupted on 14 June 2012 (SOL2012-06-14). In this work, we use data from the Solar Dynamics Observatory to model the coronal magnetic field of the active region one hour prior to eruption using a nonlinear force-free field extrapolation, and find a flux rope reaching a maximum height of 150 Mm above the photosphere. Estimations of the average twist of the strongly asymmetric extrapolated flux ... [READ MORE]

Authors: James, A. W., Valori, G., Green, L. M., Liu, Y., Cheung, M. C. M., Guo, Y., van Driel-Gesztelyi, L.
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted in ApJL
Last Modified: 2018-02-28 14:01
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Analysis of a global Moreton wave observed on October 28, 2003    

Nicole Muhr   Submitted: 2009-11-24 04:29

We study the well pronounced Moreton wave that occurred in association with the X17.2 flare/CME event of October 28, 2003. This Moreton wave is striking for its global propagation and two separate wave centers, which implies that two waves were launched simultaneously. The mean velocity of the Moreton wave, tracked within different sectors of propagation direction, lies in the range of v ~ 900 − 1100 km/s with two sectors showing wave deceleration. The perturbation profile analysis of the wave indicates amplitude growth followed by amplitude weakening and broadening of the perturbation profile, which is consistent with a disturbance first driven and then evolving into a freely propagating wave. The EIT wavefront is found to lie on the same kinematical curve as the Moreton ... [READ MORE]

Authors: N. Muhr, B. Vrsnak, M. Temmer, A. M. Veronig, J. Magdalenic
Projects: None,SoHO-EIT,SoHO-MDI,SoHO-LASCO,TRACE

Publication Status: accepted for ApJ
Last Modified: 2009-11-24 12:36
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Coronal loop seismology using damping of standing kink oscillations by mode coupling II. additional physical effects and Bayesian analysis    

David James Pascoe   Submitted: 2017-01-19 01:29

The strong damping of kink oscillations of coronal loops can be explained by mode coupling. The damping envelope depends on the transverse density profile of the loop. Observational measurements of the damping envelope have been used to determine the transverse loop structure which is important for understanding other physical processes such as heating. The general damping envelope describing the mode coupling of kink waves consists of a Gaussian damping regime followed by an exponential damping regime. Recent observational detection of these damping regimes has been employed as a seismological tool. We extend the description of the damping behaviour to account for additional physical effects, namely a time-dependent period of oscillation, the presence of additional longitudinal ... [READ MORE]

Authors: D. J. Pascoe, S. Anfinogentov, G. Nistico, C. R. Goddard, and V. M. Nakariakov
Projects: SDO-AIA

Publication Status: A&A (accepted)
Last Modified: 2017-01-19 13:31
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Reconnection and energy release rates in a two-ribbon flare    

Christiane Miklenic   Submitted: 2006-10-05 03:35

The aim of this study was to derive the local reconnection rate (coronal electric field) and the global reconnection rate (magnetic flux change rate), as well as the energy release rate (Poynting flux), in a two-ribbon flare from chromospheric/photospheric observations. Furthermore, we tested whether equal shares of positive and negative magnetic flux are involved in the flare process. A well-observed GOES M3.9 two-ribbon flare was analyzed. The required observables (ribbon expansion velocity, newly brightened area, and magnetic field strength at the ribbon front) were extracted from the TRACE 1600 A and Kanzelhoehe H-alpha image time series, and a SOHO MDI magnetogram. Furthermore, the ratio of the converted positive vs. negative magnetic flux was determined. Both RHESSI ... [READ MORE]

Authors: Miklenic, C. H., Veronig, A. M., Vrsnak, B., and Hanslmeier, A.
Projects: RHESSI,SoHO-MDI,TRACE

Publication Status: A&A (accepted)
Last Modified: 2006-10-18 03:54
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An Early Diagnostics of the Geoeffectiveness of Solar Eruptions from Photospheric Magnetic Flux Observations: The Transition from SOHO to SDO    

Ilya Chertok   Submitted: 2017-02-20 23:55

In our previous articles (Chertok et al.: 2013, Solar Phys. 282, 175, and 2015, Solar Phys. 290, 627), we presented a preliminary tool for the early diagnostics of the geoeffectiveness of solar eruptions based on the estimate of the total unsigned line-of-sight photospheric magnetic flux in accompanying extreme-ultraviolet arcades and dimmings. This tool was based on the analysis of eruptions observed in 1996-2005 with SOHO/EIT and MDI. Empirical relationships were obtained to estimate the probable importance of upcoming space weather disturbances caused by an eruption, which just occurred, without data on the associated coronal mass ejections. It was possible to estimate the intensity of a non-recurrent geomagnetic storm (GMS) and Forbush decrease (FD), as well as their onset and peak ... [READ MORE]

Authors: I.M. Chertok, V.V. Grechnev, A.A. Abunin
Projects: SDO-AIA,SDO-HMI,SoHO-EIT,SoHO-MDI

Publication Status: Solar Physics, accepted
Last Modified: 2017-02-21 15:43
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Growing transverse oscillations of a multistranded loop observed by SDO/AIA    

Tongjiang Wang   Submitted: 2012-04-09 18:38

The first evidence of transverse oscillations of a multistranded loop with growing amplitudes and internal coupling observed by the Atomspheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) is presented. The loop oscillation event occurred on 2011 March 8, triggered by a CME. The multiwavelength analysis reveals the presence of multithermal strands in the oscillating loop, whose dynamic behaviors are temperature-dependent, showing differences in their oscillation amplitudes, phases and emission evolution. The physical parameters of growing oscillations of two strands in 171 A are measured and the 3-D loop geometry is determined using STEREO-A/EUVI data. These strands have very similar frequencies, and between two 193 A strands a quarter-period phase delay sets up. ... [READ MORE]

Authors: Tongjiang Wang, Leon Ofman, Joseph M. Davila, Yang Su
Projects: SDO-AIA

Publication Status: Accepted by ApJ Letter (2012)
Last Modified: 2012-04-10 11:29
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Turbulent kinetic energy in the energy balance of a solar flare    

Eduard Kontar   Submitted: 2017-04-01 08:49

The energy released in solar flares derives from a reconfiguration of magnetic fields to a lower energy state, and is manifested in several forms, including bulk kinetic energy of the coronal mass ejection, acceleration of electrons and ions, and enhanced thermal energy that is ultimately radiated away across the electromagnetic spectrum from optical to X-rays. Using an unprecedented set of coordinated observations, from a suite of instruments, we here report on a hitherto largely overlooked energy component -- the kinetic energy associated with small-scale turbulent mass motions. We show that the spatial location of, and timing of the peak in, turbulent kinetic energy together provide persuasive evidence that turbulent energy may play a key role in the transfer of energy in solar flares. ... [READ MORE]

Authors: Kontar, E. P.; Perez, J. E.; Harra, L. K.; Kuznetsov, A. A.; Emslie, A. G.; Jeffrey, N. L. S.; Bian, N. H.; Dennis, B. R.
Projects: None,Hinode/EIS,RHESSI,SDO-AIA,SDO-HMI

Publication Status: to be published in Physical Review Letters
Last Modified: 2017-04-02 19:06
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Determining Heating Rates in Reconnection Formed Flare Loops of the M8.0 Flare on 2005 May 13    

Wenjuan Liu   Submitted: 2013-04-17 10:18

We analyze and model an M8.0 flare on 2005 May 13 observed by the Transition Region and Coronal Explorer (TRACE) and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to determine the energy release rate from magnetic reconnection that forms and heats numerous flare loops. The flare exhibits two ribbons in UV 1600 {AA} emission. Analysis shows that the UV light curve at each flaring pixel rises impulsively within a few minutes, and decays slowly with a timescale longer than 10 minutes. Since the lower atmosphere (the transition region and chromosphere) responds to energy deposit nearly instantaneously, the rapid UV brightening is thought to reflect the energy release process in the newly formed flare loop rooted at the foot point. In this paper, we utilize the spatially ... [READ MORE]

Authors: Wen-Juan Liu, Jiong Qiu, Dana W. Longcope, Amir Caspi
Projects: TRACE

Publication Status: accepted for publication in The Astrophysical Journal
Last Modified: 2013-04-17 12:20
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Interplanetary shocks lacking type II radio bursts    

Nat Gopalswamy   Submitted: 2010-01-18 14:06

We report on the radio-emission characteristics of 222 interplanetary (IP) shocks. A surprisingly large fraction of the IP shocks (~34%) is radio quiet (i.e., the shocks lacked type II radio bursts). The CMEs associated with the RQ shocks are generally slow (average speed ~535 km/s) and only ~40% of the CMEs were halos. The corresponding numbers for CMEs associated with radio loud (RL) shocks are 1237 km/s and 72%, respectively. The RQ shocks are also accompanied by lower peak soft X-ray flux. CMEs associated with RQ (RL) shocks are generally accelerating (decelerating). The kinematics of CMEs associated with the km type II bursts is similar to those of RQ shocks, except that the former are slightly more energetic. Comparison of the shock The RQ shocks seem to be mostly subcritical and ... [READ MORE]

Authors: N. Gopalswamy, H. Xie, P. Makela, S. Akiyama, S. Yashiro, M. L. Kaiser, R. A. Howard, J.-L. Bougeret
Projects: SoHO-LASCO

Publication Status: Astrophys. J. in press
Last Modified: 2010-01-19 09:08
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Correlation Between Speeds of CMEs and the Intensity of Geomagnetic Storms    

Vasyl Yurchyshyn   Submitted: 2003-04-02 16:10

We studied the relationship between the projection speed of CMEs, evaluated from SOHO/LASCO images, and the hourly averaged magnitude of the B_z component of the magnetic field in an interplanetary ejecta, as measured by the ACE magnetometer in the GSM coordinate system. For CMEs, that originate at the central part of the solar disk, we found that the intensity of B_z is a function of the speed of the CME. We also present data which support earlier conclusions about the correlation of B_z and the Dst index. A possible application of the results to space weather forecasting is discussed.

Authors: Vasyl Yurchyshyn, Haimin Wang, Valentyna Abramenko
Projects: Soho-LASCO

Publication Status: Space Weather (accepted)
Last Modified: 2004-10-13 09:41
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Multi-thermal dynamics and energetics of a coronal mass ejection in the low solar atmosphere    

Iain Hannah   Submitted: 2013-04-26 09:02

Aims: The aim of this work is to determine the multi-thermal characteristics and plasma energetics of an eruptive plasmoid and occulted flare observed by the Solar Dynamics Observatory?s Atmospheric Imaging Assembly (SDO/AIA). Methods: We study a 2010 Nov. 3 event (peaking at 12:20 UT in GOES soft X-rays) of a coronal mass ejection and occulted flare that demonstrates the morphology of a classic erupting flux rope. The high spatial and time resolution and six coronal channels of the SDO/AIA images allows the dynamics of the multi-thermal emission during the initial phases of eruption to be studied in detail. The differential emission measure is calculated, using an optimized version of a regularized inversion method, for each pixel across the six channels at different times, resulting ... [READ MORE]

Authors: I. G. Hannah and E. P. Kontar
Projects: SDO-AIA

Publication Status: Published by A&A (movie available in electronic version)
Last Modified: 2013-04-26 10:14
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Orientations of LASCO Halo CMEs and Their Connection to the Flux Rope Structure of Interplanetary CMEs    

Vasyl Yurchyshyn   Submitted: 2007-01-25 15:46

Coronal mass ejections (CMEs) observed near the Sun via LASCO coronographic imaging are the most important solar drivers of geomagnetic storms. ICMEs, their interplanetary, near-Earth counterparts, can be detected in-situ, for example, by the Wind and ACE spacecraft. An ICME usually exhibits a complex structure that very often includes a magnetic cloud (MC). They can be commonly modelled as magnetic flux ropes and there is observational evidence to expect that the orientation of a halo CME elongation corresponds to the orientation of the flux rope. In this study, we compare orientations of elongated CME halos and the corresponding MCs, measured by Wind and ACE spacecraft. We characterize the MC structures by using the Grad-Shafranov reconstruction technique and three MC fitting methods to ... [READ MORE]

Authors: V. Yurchyshyn, Q.Hu, R.P. Lepping, B.J. Lynch & J. Krall
Projects: SoHO-LASCO

Publication Status: Adv. Space Res., http://dx.doi.org/10.1016/j.asr.2007.01.059
Last Modified: 2007-02-12 10:47
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Preconditioning of interplanetary space due to transient CME disturbances    

Manuela Temmer   Submitted: 2016-12-20 01:38

Interplanetary space is characteristically structured mainly by high-speed solar wind streams emanating from coronal holes and transient disturbances such as coronal mass ejections (CMEs). While high-speed solar wind streams pose a continuous outflow, CMEs abruptly disrupt the rather steady structure causing large deviations from the quiet solar wind conditions. For the first time, we give a quantification of the duration of disturbed conditions (preconditioning) for interplanetary space caused by CMEs. To this aim, we investigate the plasma speed component of the solar wind and the impact of in situ detected CMEs (ICMEs), compared to different background solar wind models (ESWF, WSA, persistence model) for the time range 2011-2015. We quantify in terms of standard error measures the ... [READ MORE]

Authors: M. Temmer, M. A. Reiss, L. Nikolic, S. J. Hofmeister, A. M. Veronig
Projects: ACE

Publication Status: Accepted for publication in The Astrophysical Journal
Last Modified: 2016-12-21 12:21
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Evidence of Rapid Flux Emergence Associated with the M8.7 Flare on 2003 July 26    

Haimin Wang   Submitted: 2003-11-24 20:48

In this paper, we present a detailed study of the M8.7 flare that occurred on July 26, 2002, using data from Big Bear Solar Observatory (BBSO), Ramaty High Energy Solar Spectroscopic Imager (RHESSI), Transition Region and Coronal Explorer (TRACE) and Solar and Heliospheric Observatory (SOHO). This flare has similar interesting properties to a number of flares that we studied previously, such as a rapid increase of magnetic flux in one polarity, and an increase in transverse fields and magnetic shear associated with the flare. However, this event had most comprehensive observations, in particular, the high resolution high cadence BBSO vector magnetograph observations. At the time of the flare, across the flare neutral line, there was a sudden emergence of magnetic flux at the ... [READ MORE]

Authors: H. Wang, J. Qiu, J. Jing, T. Spirock, V. Yurchyshyn, V. Abramenko, H. Ji and P.R. Goode
Projects: RHESSI,Soho-MDI,TRACE

Publication Status: ApJ, (submitted)
Last Modified: 2003-11-24 20:48
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Spectropolarimetric Insight into Plasma-Sheet Dynamics of a Solar Flare    

Ryan French   Submitted: 2019-12-02 07:38

We examine spectropolarimetric data from the CoMP instrument, acquired during the evolution of the September 10th 2017 X8.2 solar flare on the western solar limb. CoMP captured linearly polarized light from two emission lines of Fe XIII at 1074.7 and 1079.8 nm, from 1.03 to 1.5 solar radii. We focus here on the hot plasma-sheet lying above the bright flare loops and beneath the ejected CME. The polarization has a striking and coherent spatial structure, with unexpectedly small polarization aligned with the plasma-sheet. By elimination, we find that small-scale magnetic field structure is needed to cause such significant depolarization, and suggest that plasmoid formation during reconnection (associated with the tearing mode instability) creates magnetic structure on scales below ... [READ MORE]

Authors: Ryan J. French, Philip G. Judge, Sarah A. Matthews, Lidia van Driel-Gesztelyi
Projects: MLSO/CoMP,SDO-AIA

Publication Status: Accepted for publication to ApJ Letters
Last Modified: 2019-12-04 11:28
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Imaging Spectroscopy of Solar Radio Burst Fine Structures    

Eduard Kontar   Submitted: 2017-11-16 00:25

Solar radio observations provide a unique diagnostic of the outer solar atmosphere. However, the inhomogeneous turbulent corona strongly affects the propagation of the emitted radio waves, so decoupling the intrinsic properties of the emitting source from the effects of radio-wave propagation has long been a major challenge in solar physics. Here we report quantitative spatial and frequency characterization of solar radio burst fine structures observed with the LOw Frequency Array (LOFAR), an instrument with high time resolution that also permits imaging at scales much shorter than those corresponding to radio-wave propagation in the corona. The observations demonstrate that radio-wave propagation effects, and not the properties of the intrinsic emission source, dominate the observed ... [READ MORE]

Authors: E. P. Kontar, S. Yu, A. A. Kuznetsov, A. G. Emslie, B. Alcock, N. L. S. Jeffrey, V. N. Melnik, N. H. Bian, P. Subramanian
Projects: Other,SDO-AIA

Publication Status: https://www.nature.com/articles/s41467-017-01307-8
Last Modified: 2017-11-16 23:31
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The Thermal Properties of Solar Flares over Three Solar Cycles Using GOES X-Ray Observations    

Daniel Ryan   Submitted: 2012-05-31 10:13

Solar flare X-ray emission results from rapidly increasing temperatures and emission measures in flaring active region loops. To date, observations from the X-Ray Sensor (XRS) onboard the Geostationary Operational Environmental Satellite (GOES) have been used to derive these properties, but have been limited by a number of factors, including the lack of a consistent background subtraction method capable of being automatically applied to large numbers of flares. In this paper, we describe an automated temperature and emission measure-based background subtraction method (TEBBS), which builds on the methods of Bornmann (1990). Our algorithm ensures that the derived temperature is always greater than the instrumental limit and the pre-flare background temperature, and that the temperature and ... [READ MORE]

Authors: Daniel F. Ryan, Ryan O. Milligan, Peter T. Gallagher, Brian R. Dennis, A. Kim Tolbert, Richard A. Schwartz, C. Alex Young
Projects: GOES X-rays

Publication Status: ApJS (accepted 2012-05-24)
Last Modified: 2012-05-31 16:01
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The energetics of a global shock wave in the low solar corona    

David Long   Submitted: 2015-01-08 04:10

As the most energetic eruptions in the solar system, coronal mass ejections (CMEs) can produce shock waves at both their front and flanks as they erupt from the Sun into the heliosphere. However, the amount of energy produced in these eruptions, and the proportion of their energy required to produce the waves, is not well characterised. Here we use observations of a solar eruption from 2014 February 25 to estimate the energy budget of an erupting CME and the globally-propagating "EIT wave" produced by the rapid expansion of the CME flanks in the low solar corona. The "EIT wave" is shown using a combination of radio spectra and extreme ultraviolet images to be a shock front with a Mach number greater than one. Its initial energy is then calculated using the Sedov-Taylor blast-wave ... [READ MORE]

Authors: David M. Long, Deborah Baker, David R. Williams, Eoin P. Carley, Peter T. Gallagher, Pietro Zucca
Projects: Hinode/EIS,SDO-AIA

Publication Status: Accepted for publication in ApJ
Last Modified: 2015-01-09 12:50
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Observational Evidence of Magnetic Reconnection for Brightenings and Transition Region Arcades in IRIS observations    

Jie Zhao   Submitted: 2017-01-30 20:21

By using a new method of forced-field extrapolation, we study the emerging flux region AR 11850 observed by the Interface Region Imaging Spectrograph (IRIS) and Solar Dynamical Observatory (SDO). Our results suggest that the bright points (BPs) in this emerging region have responses in lines formed from the upper photosphere to the transition region, with a relatively similar morphology. They have an oscillation of several minutes according to the Atmospheric Imaging Assembly (AIA) data at 1600 and 1700 A . The ratio between the BP intensities measured in 1600 A and 1700 A filtergrams reveals that these BPs are heated differently. Our analysis of the Helioseismic and Magnetic Imager (HMI) vector magnetic field and the corresponding topology in AR11850 indicates that the BPs are located at ... [READ MORE]

Authors: Jie Zhao, Brigitte Schmieder, Hui Li, Etienne Pariat, Xiaoshuai Zhu, Li Feng, Michalina Grubecka
Projects: IRIS,SDO-AIA,SDO-HMI

Publication Status: Accepted by ApJ. In Press.
Last Modified: 2017-01-31 11:46
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Modeling Magnetic Field Structure of a Solar Active Region Corona using Nonlinear Force-Free Fields in Spherical Geometry    

Yang Guo   Submitted: 2012-10-21 08:16

We test a nonlinear force-free field (NLFFF) optimization code in spherical geometry using an analytical solution from Low and Lou. Several tests are run, ranging from idealized cases where exact vector field data are provided on all boundaries, to cases where noisy vector data are provided on only the lower boundary (approximating the solar problem). Analytical tests also show that the NLFFF code in the spherical geometry performs better than that in the Cartesian one when the field of view of the bottom boundary is large, say, $20^circ imes 20^circ$. Additionally, We apply the NLFFF model to an active region observed by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) both before and after an M8.7 flare. For each observation time, we initialize ... [READ MORE]

Authors: Y. Guo, M. D. Ding, Y. Liu, X. D. Sun, M. L. DeRosa, T. Wiegelmann
Projects: SDO-AIA,SDO-HMI

Publication Status: accepted for publication in ApJ
Last Modified: 2012-10-22 10:26
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Observation of Loop Connectivity Change in a Solar Flare Triggered by Loop-Loop Interaction    

Linhui Sui   Submitted: 2005-09-30 08:37

Magnetic reconnection between two adjacent magnetic loops or arcades has been a longstanding model for solar flares. However, the observations supporting this quadrupolar flare model are mainly post-reconnection observations. We present a set of flare observations in EUV, X-rays and Há which shows that a pre-flare loop changed its connectivity soon after the start of an M1 flare on June 2, 2002. A large arcade of loops seen in EUV expanded slowly at ~6 km/s about 3 min before the start of the flare. Another smaller EUV loop expanded rapidly at ~100 km/s at the start of the flare. After ~20 s, the smaller loop then reconnected with magnetic loops within the arcade, resulting in two new post-reconnection loops. The newly-formed, smaller EUV loop, with a long cusp at the looptop, was also ... [READ MORE]

Authors: Sui, L., Holman, G. D., Dennis, B. R.
Projects: RHESSI,Soho-MDI,TRACE

Publication Status: submitted to ApJ
Last Modified: 2005-09-30 08:37
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Maximum CME speed as an indicator of solar and geomagnetic activities    

Ali Kilcik   Submitted: 2011-11-18 12:31

We investigate the relationship between the monthly averaged maximal speeds of coronal mass ejections (CMEs), international sunspot number (ISSN), and the geomagnetic Dst and Ap indices covering the 1996-2008 time interval (solar cycle 23). Our new findings are as follows. (1) There is a noteworthy relationship between monthly averaged maximum CME speeds and sunspot numbers, Ap and Dst indices. Various peculiarities in the monthly Dst index are correlated better with the fine structures in the CME speed profile than that in the ISSN data. (2) Unlike the sunspot numbers, the CME speed index does not exhibit a double peak maximum. Instead, the CME speed profile peaks during the declining phase of solar cycle 23. Similar to the Ap index, both CME speed and the Dst indices lag behind the ... [READ MORE]

Authors: A. Kilcik, V.B. Yurchyshyn, V. Abramenko, P.R. Goode, N. Gopalswamy, A. Ozguc, J.P. Rozelot
Projects: SoHO-LASCO

Publication Status: Published in 2011, Astrophys. J. 727, article id. 44 DOI: 10.1088/0004-637X/727/1/44
Last Modified: 2011-11-22 02:49
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The early phases of a solar prominence eruption and associated flare: a multi-wavelength analysis    

Cristina Chifor   Submitted: 2006-08-20 18:34

Aims: We aim to examine the precursor phases and early evolution of a prominence eruption associated with a M4-class flare and a partial halo coronal mass ejection (CME) observed on 2005 July 27. Our main goal is to investigate the precursor eruption signatures observed in EUV, X-ray and microwave emission and their relation to the prominence destabilisation.

Methods: We perform a multi-wavelength study of the prominence morphology and motion using high-cadence and spatial resolution EUV 171 Å images from the TRACE satellite. The high-temperature flare radiative emission in soft and hard X-rays are analysed through imaging and spectral modeling with RHESSI. Complementary microwave images (17 GHz and 34 GHz) from NoRH are also investigated.

Results: The activation of ... [READ MORE]

Authors: C. Chifor, H. E. Mason, D. Tripathi, H. Isobe, & A. Asai
Projects: RHESSI,SoHO-EIT,SoHO-LASCO,TRACE

Publication Status: A&A accepted, in press
Last Modified: 2006-08-20 18:40
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The Kinematics and Plasma Properties of a Solar Surge Triggered by Chromospheric Activity in AR11271    

Dr. A.K. Srivastava   Submitted: 2013-04-28 05:36

We observe a solar surge in NOAA AR11271 using the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly 304 ? image data on 2011 August 25. The surge rises vertically from its origin up to a height of ≈65 Mm with a terminal velocity of ≈100 km s-1, and thereafter falls and fades gradually. The total lifetime of the surge was ≈20 minutes. We also measure the temperature and density distribution of the observed surge during its maximum rise and find an average temperature and a density of 2.0 MK and 4.1 ? 109 cm-3, respectively. The temperature map shows the expansion and mixing of cool plasma lagging behind the hot coronal plasma along the surge. Because SDO/HMI temporal image data do not show any detectable evidence of significant photospheric magnetic field ... [READ MORE]

Authors: Kayshap, P.; Srivastava, Abhishek K.; Murawski, K.
Projects: SDO-AIA

Publication Status: The Astrophysical Journal, Volume 763, Issue 1, article id. 24, 12 pp. (2013).
Last Modified: 2013-04-30 12:04
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Studies of Isolated and Non-isolated Photospheric Bright Points in an Active Region Observed by the New Vacuum Solar Telescope    

Yanxiao Liu   Submitted: 2018-03-25 22:15

Properties of photospheric bright points (BPs) near an active region have been studied in TiO λ 7058 ? images observed by the New Vacuum Solar Telescope of the Yunnan Observatories. We developed a novel recognition method that was used to identify and track 2010 BPs. The observed evolving BPs are classified into isolated (individual) and non-isolated (where multiple BPs are observed to display splitting and merging behaviors) sets. About 35.1% of BPs are non-isolated. For both isolated and non-isolated BPs, the brightness varies from 0.8 to 1.3 times the average background intensity and follows a Gaussian distribution. The lifetimes of BPs follow a lognormal distribution, with characteristic lifetimes of (267 ? 140) s and (421 ? 255) s, respectively. Their size also follows ... [READ MORE]

Authors: Yanxiao Liu, Yongyuan Xiang, Robertus Erd?lyi, Zhong Liu, Dong Li, Zongjun Ning, Yi Bi,Ning Wu, and Jun Lin
Projects: New Vacuum Solar Telescope (NVST)

Publication Status: Accepted for publication in ApJ
Last Modified: 2018-03-28 11:37
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Solar connections of geoeffective magnetic structures    

Nat Gopalswamy   Submitted: 2009-01-03 09:51

Coronal mass ejections (CMEs) and high-speed solar wind streams (HSS) are two solar phenomena that produce large-scale structures in the interplanetary (IP) medium. CMEs evolve into interplanetary CMEs (ICMEs) and the HSS result in corotating interaction regions (CIRs) when they interact with preceding slow solar wind. This paper summarizes the properties of these structures and describes their geoeffectiveness. The primary focus is on the intense storms of solar cycle 23 because this is the first solar cycle during which simultaneous, extensive, and uniform data on solar, IP, and geospace phenomena exist. After presenting illustrative examples of coronal holes and CMEs, I discuss the internal structure of ICMEs, in particular the magnetic clouds (MCs). I then discuss how the magnetic ... [READ MORE]

Authors: N. Gopalswamy
Projects: SoHO-EIT,SoHO-LASCO

Publication Status: J. of Atmospheric and Solar-Terrestrial Physics, 70, 2078 - 2100, 2008, doi:10.1016/j.jastp.2008.06.010
Last Modified: 2009-01-05 14:14
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High time resolution observations of solar H-alpha flares - II Search for signatures of electron beam heating    

Krzysztof Radziszewski   Submitted: 2011-10-20 02:51

Aims. The Hα emission of solar flare kernels and associated hard X-ray (HXR) emission often show similar time variations but their light curves are shifted in time by energy transfer mechanisms. We searched for fast radiative response of the chromosphere in the H-alpha line as a signature of electron beam heating. Methods. We investigate the time differences with sub-second resolution between the Hα line emission observed with a Multi-channel Subtractive Double Pass (MSDP) spectrograph on the Large Coronagraph and Horizontal Telescope at Bialkow Observatory, Poland, and HXR emission recorded by the RHESSI spacecraft during several flares, greatly extending our earlier analysis (Paper I) to flares between 2003 and 2005. Results. For 16 H-alpha flaring kernels, observed in 12 ... [READ MORE]

Authors: K. Radziszewski, P. Rudawy, and K. J. H. Phillips
Projects: SECIS Instrument (Wroclaw)

Publication Status: Article accepted for publication in Section 9. The Sun of Astronomy and Astrophysics. The official date of acceptance is 13/09/2011.
Last Modified: 2012-11-12 03:57
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Near-Sun Flux Rope Structure of CMEs    

Hong Xie   Submitted: 2013-01-07 13:08

We have used the Krall's flux-rope model (Krall and St. Cyr, Astrophys. J. 2006, 657, 1740) (KFR) to fit 23 magnetic cloud (MC)-CMEs and 30 non-cloud ejecta (EJ)-CMEs in the Living With a Star (LWS) Coordinated Data Analysis Workshop (CDAW) 2011 list. The KFR-fit results shows that the CMEs associated with MCs (EJs) have been deflected closer to (away from) the solar disk center (DC), likely by both the intrinsic magnetic structures inside an active region (AR) and ambient magnetic structures (e.g. nearby ARs, coronal holes, and streamers, etc.). The mean propagation latitudes and longitudes of the EJ-CMEs (18◦, 11◦) were larger than those of the MC-CMEs (11◦, 6◦) by 7◦ and 5◦, respectively. Furthermore, the KFR-fit widths showed that the ... [READ MORE]

Authors: H. Xie, N. Gopalswamy, and O. C. St.Cyr
Projects: SoHO-EIT,SoHO-LASCO

Publication Status: published in Solar Physics 2013
Last Modified: 2013-01-10 09:37
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How Many Twists Do Solar Coronal Jets Release?    

Jiajia Liu   Submitted: 2019-05-24 07:46

Highly twisted magnetic flux ropes, with finite length, are subject to kink instabilities, and could lead to a number of eruptive phenomena in the solar atmosphere, including flares, coronal mass ejections (CMEs) and coronal jets. The kink instability threshold, which is the maximum twist a kink-stable magnetic flux rope could contain, has been widely studied in analytical models and numerical simulations, but still needs to be examined by observations. In this article, we will study twists released by 30 off-limb rotational solar coronal jets, and compare the observational findings with theoretical kink instability thresholds. We have found that: 1) the number of events with more twist release becomes less; 2) each of the studied jets has released a twist number of at least 1.3 turns (a ... [READ MORE]

Authors: Jiajia Liu, Yuming Wang, Robertus Erd?lyi
Projects: SDO-AIA

Publication Status: Accepted for publication in Frontiers in Astronomy and Space Sciences
Last Modified: 2019-05-24 10:19
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Morphology and density of post-CME current sheets    

Bojan Vrsnak   Submitted: 2009-02-25 06:18

Eruption of a coronal mass ejection (CME) drags and ''opens'' the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and the field relaxation by magnetic reconnection. We analyze physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to check if the interpretation of this phenomenon in terms of reconnecting current sheet is consistent with the observations. The study is focused on measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of rays indicates that they occur as a consequence of Petschek-like reconnection in the large scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows ... [READ MORE]

Authors: Vrsnak, B., Poletto, G., Vujic, E., Vourlidas, A., Ko, Y.-K., Raymond, J. C., Ciaravella, A., Zic, T., Webb, D. F., Bemporad, A., Landini, F., Schettino, G., Jacobs, C., Suess, S. T.
Projects: SoHO-LASCO

Publication Status: in press
Last Modified: 2009-02-25 07:57
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Imaging Observations of Quasi-Periodic Pulsatory Non-Thermal Emission in Two-Ribbon Solar Flares    

Ivan Zimovets   Submitted: 2009-06-20 02:51

Using RHESSI and some auxiliary observations we examine possible connections between the spatial and temporal structure of non-thermal hard X-ray (HXR) emission sources from the two-ribbon flares of 29 May 2003 and 19 January 2005. In each of these events quasi-periodic pulsations (QPP) with time period of 1-3 minutes are evident in both hard X-rays and microwaves. The sources of non-thermal HXR emission are situated mainly at the footpoints of the flare arcade loops observed by TRACE and the SOHO/EIT instrument in the EUV range. At least one of the sources moves systematically during and after the QPP-phase in each flare. The sources move predominantly parallel to the magnetic inversion line during the 29 May flare and along flare ribbons during the QPP-phase of both flares. By contrast, ... [READ MORE]

Authors: Zimovets, I.V., Struminsky, A.B.
Projects: RHESSI,SoHO-EIT,SoHO-MDI,TRACE

Publication Status: SolPhys(accepted)
Last Modified: 2009-06-20 11:56
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A solar tornado triggered by flares?    

Navdeep Kaur Panesar   Submitted: 2012-11-29 02:12

Solar tornados are dynamical, conspicuously helical magnetic structures mainly observed as a prominence activity. We investigate and propose a triggering mechanism for the solar tornado observed in a prominence cavity by SDO/AIA on September 25, 2011. High-cadence EUV images from the SDO/AIA and the Ahead spacecraft of STEREO/EUVI are used to correlate three flares in the neighbouring active-region (NOAA 11303), and their EUV waves, with the dynamical developments of the tornado. The timings of the flares and EUV waves observed on-disk in 195AA are analyzed in relation to the tornado activities observed at the limb in 171AA. Each of the three flares and its related EUV wave occurred within 10 hours of the onset of the tornado. They have an observed causal relationship with the ... [READ MORE]

Authors: N. K. Panesar, D. E. Innes, S. K. Tiwari, B. C. Low
Projects: SDO-AIA

Publication Status: In press A&A
Last Modified: 2012-12-01 23:51
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The Relationship Between Solar Radio and Hard X-ray Emission    

Amir Caspi   Submitted: 2011-10-28 12:20

This review discusses the complementary relationship between radio and hard X-ray observations of the Sun using primarily results from the era of the Reuven Ramaty High Energy Solar Spectroscopic Imager satellite. A primary focus of joint radio and hard X-ray studies of solar flares uses observations of nonthermal gyrosynchrotron emission at radio wavelengths and bremsstrahlung hard X-rays to study the properties of electrons accelerated in the main flare site, since it is well established that these two emissions show very similar temporal behavior. A quantitative prescription is given for comparing the electron energy distributions derived separately from the two wavelength ranges: this is an important application with the potential for measuring the magnetic field strength in the ... [READ MORE]

Authors: Stephen M. White, Arnold O. Benz, Steven Christe, Frantisek Farnik, Mukul R. Kundu, Gottfried Mann, Zongjun Ning, Jean-Pierre Raulin, Adriana V. R. Silva-Valio, Pascal Saint-Hilaire, Nicole Vilmer, Alexander Warmuth
Projects: GONG,Hinode/EIS,Hinode/SOT,Hinode/XRT,Nobeyama Radioheliograph,Owens Valley Solar Array,RHESSI,SDO-AIA,SDO-HMI,SDO-EVE,SoHO-EIT,SoHO-MDI,SoHO-CDS,SoHO-LASCO,SoHO-SUMER,STEREO,TRACE

Publication Status: Published -- White, S. M., et al. 2011, Space Sci. Rev., 159, 225; DOI 10.1007/s11214-010-9708-1
Last Modified: 2011-11-17 14:19
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Onset of Photospheric Impacts and Helioseismic Waves in X9.3 Solar Flare of September 6, 2017    

Alexander Kosovichev   Submitted: 2018-05-25 11:59

The X9.3 flare of September 6, 2017, was the most powerful flare of Solar Cycle 24. It generated strong white-light emission and multiple helioseismic waves (sunquakes). By using data from Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) as well as hard X-ray data from KONUS instrument onboard WIND spacecraft, and Anti-Coincidence System (ACS) onboard the INTERGRAL space observatory, we investigate spatio-temporal dynamics of photospheric emission sources, identify sources of helioseismic waves and compare the flare photospheric dynamics with the hard X-ray (HXR) temporal profiles. The results show that the photospheric flare impacts started to develop in compact regions in close vicinity of the magnetic polarity inversion line (PIL) in the pre-impulsive ... [READ MORE]

Authors: Ivan N. Sharykin, Alexander G. Kosovichev
Projects: GOES X-rays,INTEGRAL-ACS,SDO-HMI,Wind

Publication Status: submitted to ApJ
Last Modified: 2018-05-26 17:25
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Energetics of Coronal Mass Ejections    

Prasad Subramanian   Submitted: 2005-02-07 05:51

We examine the energetics of the best examples of flux-rope CMEs observed by LASCO in 1996-2001. We find that 69% of the CMEs in our sample experience a driving power in the LASCO field of view. For these CMEs which are driven, we examine if they might be deriving most of their driving energy by coupling to the solar wind. We do not find conclusive evidence to support this hypothesis. We adopt two different methods to estimate the energy that can possibly be released by the internal magnetic fields of the CMEs. We find that the internal magnetic fields are a viable source of driving power for these CMEs.

Authors: Prasad Subramanian (IUCAA, Pune, India), Angelos Vourlidas (NRL, Washington, DC)
Projects: Soho-LASCO

Publication Status: To appear in proceedings of IAU Symposium 226, Coronal and Stellar Mass Ejections, Sept 13-17 2004, Beijing
Last Modified: 2005-02-07 05:51
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Energetic electron propagation in the decay phase of non-thermal flare emission    

Jing Huang   Submitted: 2014-06-12 01:45

On the basis of the trap-plus-precipitation model, the peculiarities of non-thermal emission in the decay phase of solar flares have been considered. The calculation formulas for the escape rate of trapped electrons into the loss cone in terms of time profiles of hard X-ray (HXR) and microwave (MW) emission have been obtained. It has been found that the evolution of the spectral indices of non-thermal emission depend on the regimes of the pitch angle diffusion of trapped particles into the loss cone. The properties of non-thermal electrons related to the HXR and MW emission of the solar flare on 2004 November 3 are studied with Nobeyama Radioheliograph, Nobeyama Radio Polarimeters, RHESSI, and Geostationary Operational Environmental Satellite observations. The spectral indices of ... [READ MORE]

Authors: Jing Huang, Yihua Yan, and Yuri T. Tsap
Projects: Nobeyama Radioheliograph

Publication Status: ApJ, Volume 787, Page 123, 2014
Last Modified: 2014-06-12 14:54
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Tracing Electron Beams in the Sun's Corona with Radio Dynamic Imaging Spectroscopy    

Bin Chen   Submitted: 2012-12-26 09:40

We report observations of type III radio bursts at decimeter wavelengths (type IIIdm bursts) -- signatures of suprathermal electron beams propagating in the low corona -- using the new technique of radio dynamic imaging spectroscopy provided by the recently upgraded Karl G. Jansky Very Large Array (VLA). For the first time, type IIIdm bursts were imaged with high time and frequency resolution over a broad frequency band, allowing electron beam trajectories in the corona to be deduced. Together with simultaneous hard X-ray (HXR) and extreme ultraviolet (EUV) observations, we show these beams emanate from an energy release site located in the low corona at a height below ~15 Mm, and propagate along a bundle of discrete magnetic loops upward into the corona. Our observations enable direct ... [READ MORE]

Authors: Bin Chen, Timothy S. Bastian, Stephen M. White, Dale E. Gary, Richard A. Perley, Michael P. Rupen, Brent R. Carlson
Projects: RHESSI,SDO-AIA,SDO-HMI,STEREO,Very Large Array

Publication Status: Accepted for publication in the Astrophysical Journal Letters. 6 pages, 5 figures
Last Modified: 2012-12-26 12:54
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Solar signatures and eruption mechanism of the 2010 August 14 CME    

Dan Seaton   Submitted: 2017-02-06 13:45

On 2010 August 14, a wide-angled coronal mass ejection (CME) was observed. This solar eruption originated from a destabilized filament that connected two active regions and the unwinding of this filament gave the eruption an untwisting motion that drew the attention of many observers. In addition to the erupting filament and the associated CME, several other low-coronal signatures that typically indicate the occurrence of a solar eruption were associated to this event. However, contrary to what is expected, the fast CME (v>900 km s−1) was accompanied by only a weak C4.4 flare. We investigate the various eruption signatures that were observed for this event and focus on the kinematic evolution of the filament in order to determine its eruption mechanism. Had this solar eruption ... [READ MORE]

Authors: Elke D'Huys, Daniel B. Seaton, Anik De Groof, David Berghmans, Stefaan Poedts
Projects: ACE,GOES X-rays,PROBA2/SWAP,SDO-AIA,SDO-HMI,SoHO-LASCO,STEREO

Publication Status: Accepted for publication in the Journal of Space Weather and Space Climate
Last Modified: 2017-02-07 23:56
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Gradual Solar Coronal Dimming and Evolution of Coronal Mass Ejection in the Early Phase    

Jianxia Cheng   Submitted: 2017-04-10 20:40

We report observations of a two-stage coronal dimming in an eruptive event of a two-ribbon flare and a fast coronal mass ejection (CME). Weak gradual dimming persists for more than half an hour before the onset of the two-ribbon flare and the fast rise of the CME. It is followed by abrupt rapid dimming. The two-stage dimming occurs in a pair of conjugate dimming regions adjacent to the two flare ribbons, and the flare onset marks the transition between the two stages of dimming. At the onset of the two-ribbon flare, transient brightenings are also observed inside the dimming regions, before rapid dimming occurs at the same places. These observations suggest that the CME structure, most probably anchored at the twin dimming regions, undergoes a slow rise before the flare onset, and its ... [READ MORE]

Authors: Qiu, Jiong; Cheng, Jianxia
Projects: SDO-AIA

Publication Status: published
Last Modified: 2017-04-11 23:29
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Properties of Solar Ephemeral Regions at the Emergence Stage    

Shuhong Yang   Submitted: 2013-12-02 18:46

For the first time, we statistically study the properties of ephemeral regions (ERs) and quantitatively determine their parameters at the emergence stage based on a sample of 2988 ERs observed by the Solar Dynamics Observatory. During the emergence process, there are three kinds of kinematic performances, i.e., separation of dipolar patches, shift of ER's magnetic centroid, and rotation of ER's axis. The average emergence duration, flux emergence rate, separation velocity, shift velocity, and angular speed are 49.3 min, 2.6 ? 10^15 Mx s^−1, 1.1 km s^−1, 0.9 km s^−1, and 0$degr$.6 min^−1, respectively. At the end of emergence, the mean magnetic flux, separation distance, shift distance, and rotation angle are 9.3 ? 10^18 Mx, 4.7 Mm, 1.1 Mm, and 12$degr$.9, ... [READ MORE]

Authors: Shuhong Yang, Jun Zhang
Projects: SDO-AIA,SDO-HMI

Publication Status: accepted for publication in ApJ
Last Modified: 2013-12-03 10:15
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Lost and found sunquake in the 6 September 2011 flare caused by beam electrons    

Valentina Zharkova   Submitted: 2018-08-07 07:54

Active region NOAA 11283 produced two X-class flares on 6 and 7 September 2011 that have been well studied by many authors. The X2.1 class flare occurred on September 6, 2011 and was associated with the first of two homologous white light flares produced by this region, but no sunquake was found with it despite the one being detected in the second flare of 7 September 2011. In this paper we present the first observation of a sunquake for the 6 September 2011 flare detected via statistical significance analysis of egression power and verified via directional holography and time-distance diagram. The surface wavefront exhibits directional preference in the north-west direction We interpret this sunquake and the associated flare emission with a combination of a radiative hydrodynamic ... [READ MORE]

Authors: Connor Macrae, Sergei Zharkov, Valentina Zharkova, Malcolm Druett, Sarah Matthews, and Tomoko Kawate
Projects: RHESSI,SDO-AIA,SDO-HMI

Publication Status: Astronomy and Astrophysics, in press
Last Modified: 2018-08-07 11:10
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Improved methods for determining the kinematics of coronal mass ejections and coronal waves    

Jason P. Byrne   Submitted: 2013-07-31 18:20

Context: The study of solar eruptive events and associated phenomena is of great importance in the context of solar and heliophysics. Coronal mass ejections (CMEs) and coronal waves are energetic manifestations of the restructuring of the solar magnetic field and mass motion of the plasma. Characterising this motion is vital for deriving the dynamics of these events and thus understanding the physics driving their initiation and propagation. The development and use of appropriate methods for measuring event kinematics is therefore imperative. Aims: Traditional approaches to the study of CME and coronal wave kinematics do not return wholly accurate nor robust estimates of the true event kinematics and associated uncertainties. We highlight the drawbacks of these approaches, and ... [READ MORE]

Authors: J. P. Byrne, D. M. Long, P. T. Gallagher, D. S. Bloomfield, S. A. Maloney, R. T. J. McAteer, H. Morgan, S. R. Habbal
Projects: SDO-AIA,SoHO-EIT,SoHO-LASCO,STEREO

Publication Status: Accepted
Last Modified: 2013-08-01 11:17
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Elementary Loop Structures in the Solar Corona Analyzed from TRACE Triple-Filter Images    

Markus J. Aschwanden   Submitted: 2005-06-06 11:55

This study represents the first quantitative analysis of the multi-thread structure of coronal loops. We analyzed a set of 234 fine loop threads observed with TRACE triple-filter images at wavelengths of 171, 195, and 284 A. The cross-sectional flux profiles are simultaneously forward-fitted in all three filters with the superposition of a cospatial gaussian and linear background functions. We fit a general multi-temperature differential emission measure (DEM) distribution to each cross-section, as well as the special case of a single-temperature or isothermal DEM. We perform these forward-fits at ~ 18,000 loop positions and find that this geometric model could be fitted in ~ 3500 cases (within a chi_red < 1.5), while all other cases require more complex geometric models of ... [READ MORE]

Authors: Markus J. Aschwanden & Richard W. Nightingale
Projects: TRACE

Publication Status: ApJ, Vol 633 (2005 Nov 1 issue, in press)
Last Modified: 2005-07-18 11:51
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Direct Evidence for a Fast CME Driven by the Prior Formation and Subsequent Destabilization of a Magnetic Flux Rope    

Spiros Patsourakos   Submitted: 2012-12-14 03:59

Magnetic flux ropes play a central role in the physics of Coronal Mass Ejections (CMEs). Although a flux rope topology is inferred for the majority of coronagraphic observations of CMEs, a heated debate rages on whether the flux ropes pre-exist or whether they are formed on-the-fly during the eruption. Here, we present a detailed analysis of Extreme Ultraviolet observations of the formation of a flux rope during a confined flare followed about seven hours later by the ejection of the flux rope and an eruptive flare. The two flares occurred during 18 and 19 July 2012. The second event unleashed a fast (> 1000 km/s) CME. We present the first direct evidence of a fast CME driven by the prior formation and destabilization of a coronal magnetic flux rope ... [READ MORE]

Authors: S. Patsourakos, A. Vourlidas, G. Stenborg
Projects: SDO-AIA

Publication Status: ApJ, 2013 in press
Last Modified: 2012-12-14 16:10
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Performance Testing of an Off-Limb Solar Adaptive Optics System    

R.T.James McAteer   Submitted: 2015-06-25 12:13

Long-exposure spectro-polarimetry in the near-infrared is a preferred method to measure the magnetic field and other physical properties of solar prominences. In the past, it has been very difficult to observe prominences in this way with sufficient spatial resolution to fully understand their dynamical properties. Solar prominences contain highly transient structures, visible only at small spatial scales; hence they must be observed at sub-arcsecond resolution, with a high temporal cadence. An adaptive optics (AO) system capable of directly locking on to prominence structure away from the solar limb has the potential to allow for diffraction-limited spectro-polarimetry of solar prominences. We show the performance of the off-limb AO system and its expected performance at the desired ... [READ MORE]

Authors: G.E. Taylor, D. Schmidt, J. Marino, T.R. Rimmele, R.T.James McAteer
Projects: National Solar Observatory (Sac Peak)

Publication Status: Accepted
Last Modified: 2015-06-29 11:55
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Measuring and modeling the rate of separator reconnection between an emerging and existing active region    

Marika Isabel McCarthy   Submitted: 2019-11-18 10:54

Magnetic reconnection occurs when new flux emerges into the corona and becomes incorporated into the existing coronal field. A new active region (AR) emerging in the vicinity of an existing AR provides a convenient laboratory in which reconnection of this kind can be quantified. We use high time-cadence 171 $\AA$ data from SDO/AIA focused on new/old active region pair 11147/11149, to quantify reconnection. We identify new loops as brightenings within a strip of pixels between the regions. This strategy is premised on the assumption that the energy brightening a loop originates in magnetic reconnection. We catalog 301 loops observed in the 48-hour time period beginning with the emergence of AR 11149. The rate at which these loops appear between the two ARs is used to calculate the ... [READ MORE]

Authors: McCarthy, M.I., Longcope, D.W., Malanushenko, A., McKenzie, D.E.
Projects: SDO-AIA,SDO-HMI

Publication Status: accepted for publication in ApJ
Last Modified: 2019-11-18 20:03
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A large-scale search for evidence of quasi-periodic pulsations in solar flares    

Andrew Inglis   Submitted: 2016-10-24 19:30

The nature of quasi-periodic pulsations in solar flares is poorly constrained, and critically the general prevalence of such signals in solar flares is unknown. Therefore, we perform a large-scale search for evidence of signals consistent with quasi-periodic pulsations in solar flares, focusing on the 1 - 300s timescale. We analyse 675 M- and X-class flares observed by GOES in 1-8A soft X-rays between 2011 February 1 and 2015 December 31. Additionally, over the same era we analyse Fermi/GBM 15-25 keV X-ray data for each of these flares that was associated with a Fermi/GBM solar flare trigger, a total of 261 events. Using a model comparison method, we determine whether there is evidence for a substantial enhancement in the Fourier power spectrum that may be consistent with a QPP signature, ... [READ MORE]

Authors: A. R. Inglis, J. Ireland, B. R. Dennis, L. A. Hayes, P. T. Gallagher
Projects: Fermi/GBM,GOES X-rays

Publication Status: Accepted for publication in ApJ
Last Modified: 2016-10-25 12:27
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Triggering Mechanism for the Filament Eruption on 2005 September 13 in Active Region NOAA 10808    

Kaori Nagashima   Submitted: 2007-07-01 22:13

On 2005 September 13 a filament eruption accompanied by a halo CME occurred in the most flare-productive active region NOAA 10808 in Solar Cycle 23. Using multi-wavelength observations before the filament eruption on Sep. 13th, we investigate the processes leading to the catastrophic eruption. We find that the filament slowly ascended at a speed of 0.1km/s over two days before the eruption. During slow ascending, many small flares were observed close to the footpoints of the filament, where new magnetic elements were emerging. On the basis of the observational facts we discuss the triggering mechanism leading to the filament eruption. We suggest the process toward the eruption as follows: First, a series of small flares played a role in changing the topology of the loops overlying the ... [READ MORE]

Authors: Kaori Nagashima, Hiroaki Isobe, Takaaki Yokoyama, Takako T. Ishii, Takenori J. Okamoto, and Kazunari Shibata
Projects: TRACE

Publication Status: ApJ (in press), astro-ph/0706.3519
Last Modified: 2007-07-08 23:25
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Hinode/EIS observations of propagating low-frequency slow magnetoacoustic waves in fan-like coronal loops    

Tongjiang Wang   Submitted: 2009-08-03 12:43

We report the first observation of multiple-periodic propagating disturbances along a fan-like coronal structure simultaneously detected in both intensity and Doppler shift in the Fe XII 195 A line with the EUV Imaging Spectrometer (EIS) onboard Hinode. A new application of coronal seismology is provided based on this observation. We analyzed the EIS sit-and-stare mode observation of oscillations using the running difference and wavelet techniques. Two harmonics with periods of 12 and 25 min are detected. We measured the Doppler shift amplitude of 1-2 km/s, the relative intensity amplitude of 3%-5% and the apparent propagation speed of 100-120 km/s. The amplitude relationship between intensity and Doppler shift oscillations provides convincing evidence that these propagating features are ... [READ MORE]

Authors: T. J. Wang, L. Ofman, J. M. Davila, J. T. Mariska
Projects: Hinode/EIS,TRACE

Publication Status: A&A Letter, 2009, in press
Last Modified: 2009-08-04 08:07
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DESTRUCTION AND OBSERVATIONAL SIGNATURES OF SUN-IMPACTING COMETS    

John C Brown   Submitted: 2015-07-22 13:27

Motivated by recent data on comets in the low corona, we discuss destruction of "sun-impacting" comets in the dense lower atmosphere. Perihelion distances q ≲ R_{⊙}; and masses M_{o} ≫ 10^12 g are required to reach such depths. Extending earlier work on planetary atmosphere impacts to solar conditions, we evaluate the mechanisms and distribution of nucleus mass and energy loss as functions of Mo and q, and of parameter X = 2Q/ C_{H} \nu_{o}^{2}. Q is the total specific energy for ablative mass-loss, C_{H} the bow-shock heat-transfer efficiency, and \nu_{o} the solar escape speed (619 km s^−1). We discuss factors affecting Q and C_{H} and conclude that, for solar \nu_{o} , X is most likely < 1 and solar-impactors mostly ablated before decelerating. ... [READ MORE]

Authors: John C Brown, Robert W Carlson, Mark P Toner
Projects: SDO-AIA

Publication Status: ApJ (in press)
Last Modified: 2015-07-22 14:53
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Observations of quasi-periodic phenomena associated with a large blowout solar jet    

Richard Morton   Submitted: 2012-04-24 02:13

A variety of periodic phenomena have been observed in conjunction with large solar jets. We aim to find further evidence for {(quasi-)}periodic behaviour in solar jets and determine what the periodic behaviour can tell us about the excitation mechanism and formation process of the large solar jet. Using the 304 {AA} (He-II), 171 {AA} (Fe IX), 193 {AA} (Fe XII/XXIV) and 131 {AA} (Fe VIII/XXI) filters on-board the Solar Dynamic Observatory (SDO) Atmospheric Imaging Assembly (AIA), we investigate the intensity oscillations associated with a solar jet. Evidence is provided for multiple magnetic reconnection events occurring between a pre-twisted, closed field and open field lines. Components of the jet are seen in multiple SDO/AIA filters covering a wide range of temperatures, suggesting the ... [READ MORE]

Authors: R. J. Morton, A. K. Srivastava, R. Erd'elyi
Projects: SDO-AIA

Publication Status: In print
Last Modified: 2012-04-25 12:19
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Flare Productivity of Major Flaring Solar Active Regions: A Time-series Study of Photospheric Magnetic Properties    

Eo-Jin Lee   Submitted: 2018-11-03 21:16

A solar active region (AR) that produces at least one M- or X-class major flare tends to produce multiple flares during its passage across the solar disk. It will be interesting if we can estimate how flare-productive a given major flaring AR is for a time interval of several days, by investigating time series of its photospheric magnetic field properties. For this, we studied 93 major flaring ARs observed from 2010 to 2016 by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). More specifically, for each AR under study, the mean and fluctuation were calculated from an 8-day time series of each of 18 photospheric magnetic parameters extracted from the Space-weather HMI Active Region Patch (SHARP) vector magnetogram products at 12-min cadence. We then ... [READ MORE]

Authors: Eo-Jin Lee, Sung-Hong Park, Yong-Jae Moon
Projects: GOES X-rays,SDO-HMI

Publication Status: Solar Physics (accepted)
Last Modified: 2018-11-05 14:16
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Multiwavelength observations of a partially eruptive filament on 2011 September 8    

Qingmin Zhang   Submitted: 2015-03-10 19:25

In this paper, we report our multiwavelength observations of a partial filament eruption event in NOAA active region 11283 on 2011 September 8. A magnetic null point and the corresponding spine and separatrix surface are found in the active region. Beneath the null point, a sheared arcade supports the filament along the highly complex and fragmented polarity inversion line. After being activated, the sigmoidal filament erupted and split into two parts. The major part rose at the speeds of 90$-$150 km s$^{-1}$ before reaching the maximum apparent height of $\sim$115 Mm. Afterwards, it returned to the solar surface in a bumpy way at the speeds of 20$-$80 km s$^{-1}$. The rising and falling motions were clearly observed in the extreme-ultravoilet (EUV), UV, and ... [READ MORE]

Authors: Q. M. Zhang, Z. J. Ning, Y. Guo, T. H. Zhou, X. Cheng, H. S. Ji, L. Feng, T. Wiegelmann
Projects: SDO-AIA

Publication Status: Accepted for publication in ApJ
Last Modified: 2015-03-11 14:47
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Automatically Detecting and Tracking CMEs I: Separation of dynamic and quiescent components in coronagraph images    

Jason P. Byrne   Submitted: 2012-06-13 13:25

Automated techniques for detecting and tracking CMEs in coronagraph data are of ever-increasing importance for space weather monitoring and forecasting. They serve to remove the biases and tedium of human interpretation, and provide the robust analysis necessary for statistical studies across large numbers of observations. An important requirement in their operation is that they satisfactorily distinguish the CME structure from the background quiescent coronal structure (streamers, coronal holes). Many studies resort to some form of time-differencing to achieve this, despite the errors inherent in such an approach - notably spatiotemporal crosstalk. This article describes a new deconvolution technique that separates coronagraph images into quiescent and dynamic components. A set of ... [READ MORE]

Authors: Huw Morgan, Jason P. Byrne, Shadia R. Habbal
Projects: SoHO-LASCO,STEREO

Publication Status: Published
Last Modified: 2012-06-13 15:34
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Solar Open Flux Migration from Pole to Pole: Magnetic Field Reversal    

Chia-Hsien Lin   Submitted: 2017-08-27 01:58

Coronal holes are solar regions with low soft X-ray or low extreme ultraviolet intensities. The magnetic fields from coronal holes extend far away from the Sun, and thus they are identified as regions with open magnetic field lines. Coronal holes are concentrated in the polar regions during the sunspot minimum phase, and spread to lower latitude during the rising phase of solar activity. In this work, we identify coronal holes with outward and inward open magnetic fluxes being in the opposite poles during solar quiet period. We find that during the sunspot rising phase, the outward and inward open fluxes perform pole-to-pole trans-equatorial migrations in opposite directions. The migration of the open fluxes consists of three parts: open flux areas migrating across the equator, new open ... [READ MORE]

Authors: Huang, G.-H., Lin, C.-H., and Lee, L.C.
Projects: SDO-AIA,SDO-HMI

Publication Status: Scientific Report (published)
Last Modified: 2017-08-28 12:24
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Determination of the total accelerated electron rate and power using solar flare hard X-ray spectra    

Eduard Kontar   Submitted: 2018-12-27 00:43

Solar flare hard X-ray spectroscopy serves as a key diagnostic of the accelerated electron spectrum. However, the standard approach using the collisional cold thick-target model poorly constrains the lower-energy part of the accelerated electron spectrum, and hence the overall energetics of the accelerated electrons are typically constrained only to within one or two orders of magnitude. Here we develop and apply a physically self-consistent warm-target approach which involves the use of both hard X-ray spectroscopy and imaging data. The approach allows an accurate determination of the electron distribution low-energy cutoff, and hence the electron acceleration rate and the contribution of accelerated electrons to the total energy released, by constraining the coronal plasma parameters. ... [READ MORE]

Authors: Eduard P. Kontar, Natasha L. S. Jeffrey, and A. Gordon Emslie
Projects: GOES X-rays,NuSTAR,RHESSI,Wind

Publication Status: accepted for publication in ApJ
Last Modified: 2018-12-28 14:32
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Energetics of Solar Coronal Mass Ejections    

Prasad Subramanian   Submitted: 2007-01-08 21:39

Aims: To investigate if solar coronal mass ejections are driven mainly by coupling to the ambient solar wind, or through the release of internal magnetic energy. Methods: We examine the energetics of 39 flux-rope like coronal mass ejections (CMEs) from the Sun using data in the distance range $sim$ 2--20 $R_{{o}dot}$ from the Large Angle Spectroscopic Coronograph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO). This comprises a complete sample of the best examples of flux-rope CMEs observed by LASCO in 1996-2001. Results: We find that 69% of the CMEs in our sample experience a clearly identifiable driving power in the LASCO field of view. For these CMEs which are driven, we examine if they might be deriving most of their driving power by coupling to the solar wind. We do ... [READ MORE]

Authors: Prasad Subramanian (1), Angelos Vourlidas (2) ((1) Indian Institute of Astrophysics, Bangalore, India; (2) Naval Research Laboratory, Washington, DC, USA)
Projects: SoHO-LASCO

Publication Status: Accepted for publication in Astronomy and Astrophysics
Last Modified: 2007-01-08 22:20
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Observational Study Of the Quasi-Periodic Fast Propagating Magnetosonic Waves and the Associated Flare on 2011 May 30    

Yuandeng Shen   Submitted: 2012-05-01 19:31

On 2011 May 30, quasi-periodic fast propagating (QFP) magnetosonic waves accompanied by a C2.8 flare were directly imaged by the Atomospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. The QFP waves successively emanated from the flare kernel, they propagated along a cluster of open coronal loops with a phase speed of 834 km/s during the flare's rising phase, and the multiple arc-shaped wave trains can be fitted with a series of concentric circles. We generate the k-omega diagram of the Fourier power and find a straight ridge that represents the dispersion relation of the waves. Along the ridge, we find a lot of prominent nodes which represent the available frequencies of the QFP waves. On the other hand, the frequencies of the flare are also obtained by ... [READ MORE]

Authors: Yuandeng Shen, Yu Liu
Projects: SDO-AIA

Publication Status: accepted by ApJ
Last Modified: 2012-05-02 11:16
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Charge states and FIP bias of the solar wind from coronal holes, active regions, and quiet Sun    

Maria Madjarska   Submitted: 2017-01-27 00:02

Connecting in-situ measured solar-wind plasma properties with typical regions on the Sun can provide an effective constraint and test to various solar wind models. We examine the statistical characteristics of the solar wind with an origin in different types of source regions. We find that the speed distribution of coronal hole (CH) wind is bimodal with the slow wind peaking at ~400 km/s and a fast at ~600 km/s. An anti-correlation between the solar wind speeds and the O7+/O6+ ion ratio remains valid in all three types of solar wind as well during the three studied solar cycle activity phases, i.e. solar maximum, decline and minimum. The N_Fe/N_O range and its average values all decrease with the increasing solar wind speed in different types of solar wind. The N_Fe/N_O range (0.06?0.40, ... [READ MORE]

Authors: Hui Fu, Maria S. Madjarska, LiDong Xia, Bo Li, ZhengHua Huang, Zhipeng Wangguan
Projects: ACE,SoHO-EIT,SoHO-MDI

Publication Status: accepted for publication in ApJ
Last Modified: 2017-01-31 11:46
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Observational Evidence of Sausage-pinch Instability in Solar Corona by SDO/AIA    

Dr. A.K. Srivastava   Submitted: 2013-04-28 05:39

We present the first observational evidence of the evolution of sausage-pinch instability in active region 11295 during a prominence eruption using data recorded on 2011 September 12 by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We have identified a magnetic flux tube visible in AIA 304 ? that shows curvatures on its surface with variable cross-sections as well as enhanced brightness. These curvatures evolved and thereafter smoothed out within a timescale of a minute. The curved locations on the flux tube exhibit a radial outward enhancement of the surface of about 1-2 Mm (a factor of two larger than the original thickness of the flux tube) from the equilibrium position. AIA 193 ? snapshots also show the formation of bright knots and narrow ... [READ MORE]

Authors: Srivastava, A. K.; Erd?lyi, R.; Tripathi, Durgesh; Fedun, V.; Joshi, N. C.; Kayshap, P.
Projects: SDO-AIA

Publication Status: The Astrophysical Journal Letters, Volume 765, Issue 2, article id. L42, 7 pp. (2013).
Last Modified: 2013-04-30 12:03
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Genesis and impulsive evolution of the 2017 September 10 coronal mass ejection    

Astrid Veronig   Submitted: 2018-10-24 07:31

The X8.2 event of 10 September 2017 provides unique observations to study the genesis, magnetic morphology and impulsive dynamics of a very fast CME. Combining GOES-16/SUVI and SDO/AIA EUV imagery, we identify a hot ($T\approx 10-15$ MK) bright rim around a quickly expanding cavity, embedded inside a much larger CME shell ($T\approx 1-2$ MK). The CME shell develops from a dense set of large AR loops ($\gtrsim$0.5~$R_s$), and seamlessly evolves into the CME front observed in LASCO C2. The strong lateral overexpansion of the CME shell acts as a piston initiating the fast EUV wave. The hot cavity rim is demonstrated to be a manifestation of the dominantly poloidal flux and frozen-in plasma added to the rising flux rope by magnetic reconnection in the current sheet beneath. The same ... [READ MORE]

Authors: Astrid M. Veronig, Tatiana Podladchikova, Karin Dissauer, Manuela Temmer, Daniel B. Seaton, David Long, Jingnan Guo, Bojan Vrsnak, Louise Harra, Bernhard Kliem
Projects: GOES X-rays,SDO-AIA

Publication Status: ApJ (accepted)
Last Modified: 2018-10-24 10:42
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A Truly Global EUV Wave From the SOL2017-09-10 X8.2 Solar Flare-CME Eruption    

Wei Liu   Submitted: 2018-07-25 10:19

We report SDO/AIA observations of an extraordinary global extreme ultraviolet (EUV) wave triggered by the X8.2 flare-CME eruption on 2017 September 10. This was one of the best EUV waves ever observed with modern instruments, yet likely the last one of such magnitudes of Solar Cycle 24 as the Sun heads toward the minimum. Its remarkable characteristics include: (1) The wave was observed, for the first time, to traverse the full-Sun corona over the entire visible solar disk and off-limb circumference, manifesting a truly global nature, owing to its exceptionally large amplitude, e.g., with EUV enhancements by up to 300% at 1.1 Rsun from the eruption. (2) This leads to strong transmissions (besides commonly observed reflections) in and out of both polar coronal holes, which are usually ... [READ MORE]

Authors: Wei Liu, Meng Jin, Cooper Downs, Leon Ofman, Mark Cheung, and Nariaki V. Nitta
Projects: SDO-AIA

Publication Status: Accepted by ApJ Letters (as of July 24, 2018)
Last Modified: 2018-07-29 21:13
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A benchmark study for CHIANTI based on RESIK solar flare spectra    

Cristina Chifor   Submitted: 2006-12-04 03:19

Aims. To perform a benchmark analysis for the recent version of the CHIANTI atomic database (v.5.2) based on high-resolution solar flare X-ray spectra in the range 3.4 - 6.1Å from the RESIK crystal spectrometer on the CORONAS-F spacecraft.

Methods. A C5.8 flare occurring on 2003 February 22 was chosen for analysis. RESIK spectra of this flare include emission lines of He-like and H-like K,Ar, S, and Si, with some dielectronic lines. Initially, two independent plasma diagnostic techniques are employed: an emission measure (EM) loci analysis using the line fluxand the line contribution function G(T_e, N_e), and a new method based on continuum fluxes and contribution functions. We further apply a differential emission measure (DEM)analysis, from which CHIANTI synthetic spectra ... [READ MORE]

Authors: C. Chifor, G. Del. Zanna, H. E. Mason, J. Sylwester, B. Sylwester, K. J. H. Phillips
Projects: CORONAS-F/SPIRIT

Publication Status: in press (A&A)
Last Modified: 2006-12-04 10:41
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Connecting the Sun's High-Resolution Magnetic Carpet to the Turbulent Heliosphere    

Steven R Cranmer   Submitted: 2013-03-05 13:17

The solar wind is connected to the Sun's atmosphere by flux tubes that are rooted in an ever-changing pattern of positive and negative magnetic polarities on the surface. Observations indicate that the magnetic field is filamentary and intermittent across a wide range of spatial scales. However, we do not know to what extent the complex flux tube topology seen near the Sun survives as the wind expands into interplanetary space. In order to study the possible long-distance connections between the corona and the heliosphere, we developed new models of turbulence-driven solar wind acceleration along empirically constrained field lines. We used a potential-field model of the Quiet Sun to trace field lines into the ecliptic plane with unprecedented spatial resolution at their ... [READ MORE]

Authors: S. R. Cranmer, A. A. van Ballegooijen, L. N. Woolsey
Projects: National Solar Observatory (Sac Peak)

Publication Status: ApJ, in press for April 20, 2013 issue, arXiv:1303.0563
Last Modified: 2013-03-06 08:54
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DUAL TRIGGER OF TRANSVERSE OSCILLATIONS IN A PROMINENCE BY EUV FAST AND SLOW CORONAL WAVES: SDO/AIA AND STEREO/EUVI OBSERVATIONS    

Sanjay Gusain   Submitted: 2012-10-24 14:58

We analyze flare-associated transverse oscillations in a quiescent solar prominence on 8-9 September, 2010. Both the flaring active region and the prominence were located near the West limb, with a favorable configuration and viewing angle. The fulldisk extreme ultraviolet (EUV) images of the Sun obtained with high spatial and temporal resolution by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory, show flare-associated lateral oscillations of the prominence sheet. The STEREO-A spacecraft, 81.5◦ ahead of the Sun-Earth line, provides on-disk view of the flare-associated coronal disturbances. We derive the temporal profile of the lateral displacement of the prominence sheet by using ... [READ MORE]

Authors: Sanjay Gosain and Claire Foullon
Projects: National Solar Observatory (Sac Peak),SDO-AIA,STEREO

Publication Status: Accepted in ApJ
Last Modified: 2012-10-26 14:55
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Decay-less kink oscillations in coronal loops    

Valery Nakariakov   Submitted: 2013-08-22 14:49

Kink oscillations of coronal loops in an off-limb active region are detected with the Imaging Assembly Array (AIA) instruments of the Solar Dynamics Observatory (SDO) at 171~AA. We aim to measure periods and amplitudes of kink oscillations of different loops and to determinate the evolution of the oscillation phase along the oscillating loop. Oscillating coronal loops were visually identified in the field of view of SDO/AIA and STEREO/EUVI-A: the loop length was derived by three-dimensional analysis. Several slits were taken along the loops to assemble time-distance maps. We identified oscillatory patterns and retrieved periods and amplitudes of the oscillations. We applied the cross-correlation technique to estimate the phase shift between oscillations at different segments of ... [READ MORE]

Authors: S.A. Anfinogentov, G. Nistico, V. M. Nakariakov
Projects: SDO-AIA

Publication Status: A&A (accepted)
Last Modified: 2013-08-22 14:49
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Why torus-unstable solar filaments experience failed eruption?    

zhenjun zhou   Submitted: 2019-05-01 20:17

To investigate the factors that control the success and/or failure of solar eruptions, we study the magnetic field and 3-Dimensional (3D) configuration of 16 filament eruptions during 2010 July - 2013 February. All these events, i.e., erupted but failed to be ejected to become a coronal mass ejection (CME), are failed eruptions with the filament maximum height exceeding 100Mm. The magnetic field of filament source regions is approximated by a potential field extrapolation method. The filament 3D configuration is reconstructed from three vantage points by the observations of STEREO Ahead/Behind and SDO spacecraft. We calculate the decay index at the apex of these failed filaments and find that in 7 cases, their apex decay indexes exceed the theoretical threshold (ncrit=1.5) of the torus ... [READ MORE]

Authors: Zhenjun Zhou, Xin Cheng, Jie Zhang, Yuming Wang, Dong Wang, Lijuan Liu, Bin Zhuang, Jun Cui
Projects: SDO-AIA,SDO-HMI,STEREO

Publication Status: under review
Last Modified: 2019-05-03 16:05
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How Many CMEs Have Flux Ropes? Deciphering the Signatures of Shocks, Flux Ropes, and Prominences in Coronagraph Observations of CMEs    

Angelos Vourlidas   Submitted: 2012-07-05 15:46

We intend to provide a comprehensive answer to the question on whether all Coronal Mass Ejections (CMEs) have flux rope structure. To achieve this, we present a synthesis of the LASCO CME observations over the last sixteen years, assisted by 3D MHD simulations of the breakout model, EUV and coronagraphic observations from extsl{STEREO} and extsl{SDO}, and statistics from a revised LASCO CME database. We argue that the bright loop often seen as the CME leading edge is the result of pileup at the boundary of the erupting flux rope irrespective of whether a cavity or, more generally, a 3-part CME can be identified. Based on our previous work on white light shock detection and supported by the MHD simulations, we identify a new type of morphology, the `two-front' morphology. It consists of ... [READ MORE]

Authors: A. Vourlidas, B.J. Lynch, R.A. Howard, Y. Li
Projects: SoHO-LASCO,STEREO

Publication Status: to be published in Solar Physics
Last Modified: 2012-07-07 14:50
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Homologous Flux Ropes Observed by SDO/AIA    

Ting Li   Submitted: 2013-10-30 03:17

We firstly present the emph{Solar Dynamics Observatory} observations of four homologous flux ropes in active region (AR) 11745 on 2013 May 20-22. The four flux ropes are all above the neutral line of the AR, with endpoints anchoring at the same region, and have the generally similar morphology. For the first three flux ropes, they rose up with a velocity of less than 30 km s$^{-1}$ after their appearances, and subsequently their intensities at 131 {AA} decreased and the flux ropes became obscure. The fourth flux rope erupted ultimately with a speed of about 130 km s$^{-1}$ and formed a coronal mass ejection. The associated filament showed an obvious anti-clockwise twist motion at the initial stage, and the twist was estimated at 4$pi$. This indicates that kink ... [READ MORE]

Authors: Ting Li & Jun Zhang
Projects: SDO-AIA

Publication Status: Accepted in ApJL
Last Modified: 2013-10-30 16:59
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Diffraction, Refraction, and Reflection of An Extreme-Ultraviolet Wave Observed during Its Interactions with Remote Active Regions    

Yuandeng Shen   Submitted: 2013-07-31 19:06

We present observations of the diffraction, refraction, and reflection of a global extreme-ultraviolet (EUV) wave propagating in the solar corona. These intriguing phenomena are observed when the wave interacts with two remote active regions, and they together exhibit the wave property of this EUV wave. When the wave approached AR11465, it became weaker and finally disappeared in the active region, but a few minutes latter a new wavefront appeared behind the active region, and it was not concentric with the incoming wave. In addition, a reflected wave was also observed simultaneously on the wave incoming side. When the wave approached AR11459, it transmitted through the active region directly and without reflection. The formation of the new wavefront and the transmission could be ... [READ MORE]

Authors: Shen, Yuandeng; Liu, Yu; Su, Jiangtao; Li, Hui; Zhao, Ruijuan; Tian, Zhanjun; Ichimoto, Kiyoshi; Shibata, Kazunari
Projects: SDO-AIA

Publication Status: accepted by APJ letters
Last Modified: 2013-08-01 11:16
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Investigating the differential emission measure and energetics of microflares with combined SDO/AIA and RHESSI observations    

Andrew Inglis   Submitted: 2014-05-22 08:09

An important question in solar physics is whether solar microflares, the smallest currently observable flare events in X-rays, possess the same energetic properties as large flares. Recent surveys have suggested that microflares may be less efficient particle accelerators than large flares, and hence contribute less nonthermal energy, which may have implications for coronal heating mechanisms. We therefore explore the energetic properties of microflares by combining Extreme Ultraviolet (EUV) and X-ray measurements. We present forward-fitting differential emission measure (DEM) analysis of 10 microflares. The fitting is constrained by combining, for the first time, high temperature RHESSI observations and flux data from SDO/AIA. Two fitting models are tested for the DEM; a Gaussian ... [READ MORE]

Authors: A. R. Inglis, S. Christe
Projects: RHESSI,SDO-AIA

Publication Status: ApJ, accepted
Last Modified: 2014-05-26 13:03
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Microwave observations of a large-scale coronal wave with the Nobeyama radioheliograph    

Alexander Warmuth   Submitted: 2016-10-13 01:08

Context. Large-scale globally propagating waves in the solar corona have been studied extensively, mainly using extreme ultraviolet (EUV) observations. In a few events, corresponding wave signatures have been detected in microwave radioheliograms provided by the Nobeyama radioheliograph (NoRH). Several aspects of these observations seem to contradict the conclusions drawn from EUV observations. Aims. We investigate whether the microwave observations of global waves are consistent with previous findings. Methods. We revisited the wave of 1997 Sep 24, which is still the best-defined event in microwaves. We obtained radioheliograms at 17 and 34~GHz from NoRH and studied the morphology, kinematics, perturbation profile evolution, and emission mechanism of the propagating microwave ... [READ MORE]

Authors: Warmuth, A., Shibasaki, K., Iwai, K., & Mann, G.
Projects: Nobeyama Radioheliograph,SoHO-EIT

Publication Status: Astronomy & Astrophysics (2016), Volume 593, id. A102, 8 pp.
Last Modified: 2016-10-14 09:18
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Evidence of Shock-Driven Turbulence in the Solar Chromosphere    

Kevin Reardon   Submitted: 2008-10-28 15:02

We study the acoustic properties of the solar chromosphere in the high-frequency regime using a time sequence of velocity measurements in the chromospheric Ca II 854.2 nm line taken with the Interferometric Bidimensional Spectrometer (IBIS). We concentrate on quiet-Sun behavior, apply Fourier analysis, and characterize the observations in terms of the probability density functions (PDFs) of velocity increments. We confirm the presence of significant oscillatory fluctuation power above the cutoff frequency and find that it obeys a power-law distribution with frequency up to our 25~mHz Nyquist limit. The chromospheric PDFs are non-Gaussian and asymmetric and they differ among network, fibril, and internetwork regions. This suggests that the chromospheric high-frequency power is not simply ... [READ MORE]

Authors: K.P. Reardon, F. Lepreti, V. Carbone, A. Vecchio
Projects: National Solar Observatory (Sac Peak)

Publication Status: Published in Astrophys. J. Lett., v683, L207
Last Modified: 2008-11-01 10:03
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Scaling Relations in Coronal Mass Ejections and Energetic Proton Events associated with Solar Superflares    

Takuya Takahashi   Submitted: 2016-11-20 22:19

In order to discuss the potential impact of solar 'superflares' on space weather, we investigated statistical relations among energetic proton peak flux with energy higher than $ 10 \rm MeV$ ($F_p$), CME speed near the Sun ($V_{CME}$) obtained by {\it SOHO}/LASCO coronagraph and flare soft X-ray peak flux in 1-8\AA band ($F_{SXR}$) during 110 major solar proton events (SPEs) recorded from 1996 to 2014. The linear regression fit results in the scaling relations $V_{CME} \propto F_{SXR}^\alpha$, $F_p\propto F_{SXR}^?\eta$ and $F_p\propto V_{CME}^\gamma$ with $\alpha = 0.30\pm 0.04$, $\beta = 1.19 \pm 0.08$ and $\gamma = 4.35 \pm 0.50$, respectively. On the basis of simple physical assumptions, on the other hand, we derive scaling relations expressing CME mass ($M_{CME}$), CME speed and ... [READ MORE]

Authors: Takuya Takahashi, Yoshiyuki Mizuno, Kazunari Shibata
Projects: SoHO-LASCO

Publication Status: Accepted for publication in ApjL
Last Modified: 2016-11-21 12:29
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Solar Flare Geometries. I. The Area Fractal Dimension    

Markus J. Aschwanden   Submitted: 2006-11-27 16:33

In this study we investigate for the first time the fractal dimension of solar flares and find that the flare area observed in EUV wavelengths exhibits a fractal scaling. We measure the {sl area fractal dimension} $D_2$, also called {sl Hausdorff dimension}, with a box-counting method, which describes the fractal area as $A(L) propto L^{D_2}$. We apply the fractal analysis to a statistical sample of 20 GOES X- and M-class flares, including the Bastille-Day 2000-Jul-14 flare, one of the largest flares recorded in history. We find that the fractal area (normalized by the time-integrated flare area $A_f$) varies from near zero at the beginning of the flare to a maximum of $A(t)/A_f = 0.65 pm 0.12$ after the peak time of the flare, which corresponds to an area fractal dimension in ... [READ MORE]

Authors: Markus J. Aschwanden and Pascal D. Aschwanden
Projects: TRACE

Publication Status: ApJ, subm. May 2007
Last Modified: 2007-06-06 15:47
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Explosive events on subarcsecond scale in IRIS observations: a case study    

Zhenghua Huang   Submitted: 2014-11-17 20:22

We present study of a typical explosive event (EE) at subarcsecond scale witnessed by strong non-Gaussian profiles with blue- and red-shifted emission of up to 150 km/s seen in the transition-region Si iv 1402.8 Å, and the chromospheric Mg ii k 2796.4 Å and C ii 1334.5 Å observed by the Interface Region Imaging Spectrograph (IRIS) at unprecedented spatial and spectral resolution. For the first time an EE is found to be associated with very small-scale (∼120 km wide) plasma ejection followed by retraction in the chromosphere. These small-scale jets originate from a compact bright-point-like structure of ∼1.5'' size as seen in the IRIS 1330 Å images. SDO/AIA and SDO/HMI co-observations show that the EE lies in the footpoint of a complex loop-like ... [READ MORE]

Authors: Zhenghua Huang, Maria S. Madjarska, Lidong Xia, J. G. Doyle, Klaus Galsgaard, Hui Fu
Projects: IRIS,SDO-AIA,SDO-HMI

Publication Status: ApJ in press
Last Modified: 2014-11-19 09:21
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The transition from eruptive to confined flares in the same active region    

Francesco Zuccarello   Submitted: 2017-02-13 03:25

Solar flares are sudden and violent releases of magnetic energy in the solar atmosphere that can be divided in eruptive flares, when plasma is ejected from the solar atmosphere, resulting in a coronal mass ejection (CME), and confined flares when no CME is associated with the flare. We present a case-study showing the evolution of key topological structures, such as spines and fans which may determine the eruptive versus non-eruptive behavior of the series of eruptive flares, followed by confined flares, which are all originating from the same site. To study the connectivity of the different flux domains and their evolution, we compute a potential magnetic field model of the active region. Quasi-separatrix layers are retrieved from the magnetic field extrapolation. The change of behavior ... [READ MORE]

Authors: Zuccarello, Francesco P.; Chandra, Ramesh; Schmieder, Brigitte; Aulanier, Guillaume; Joshi, Reetika
Projects: SDO-AIA,SDO-HMI,SoHO-LASCO

Publication Status: Accepted for publication in Astronomy and Astrophysics
Last Modified: 2017-02-13 12:05
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CORONAL MAGNETIC FIELD MEASUREMENT FROM EUV IMAGES MADE BY THE SOLAR DYNAMICS OBSERVATORY    

Nat Gopalswamy Gopalswamy   Submitted: 2013-01-05 05:19

By measuring the geometrical properties of the coronal mass ejection (CME) flux rope and the leading shock observed on 2010 June 13 by the Solar Dynamics Observatory (SDO) mission's Atmospheric Imaging Assembly (AIA) we determine the Alfv?n speed and the magnetic field strength in the inner corona at a heliocentric distance of ~ 1.4 Rs. The basic measurements are the shock standoff distance (ΔR) ahead of the CME flux rope, the radius of curvature of the flux rope (Rc), and the shock speed. We first derive the Alfv?nic Mach number (M) using the relationship, ΔR/Rc = 0.81[(γ-1)M2 + 2]/[(γ+1)(M2-1)], where γ is the only parameter that needed to be assumed. For γ =4/3, the Mach number declined from 3.7 to 1.5 indicating shock weakening within the field of view of ... [READ MORE]

Authors: Nat Gopalswamy, Nariaki Nitta, Sachiko Akiyama, Pertti Makela, and Seiji Yashiro
Projects: SDO-AIA,SoHO-LASCO

Publication Status: The Astrophysical Journal, 744, 72, 2012
Last Modified: 2013-01-07 12:46
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Solar Sources of 3He-rich Solar Energetic Particle Events in Solar Cycle 24    

Nariaki Nitta   Submitted: 2015-05-26 22:40

Using high-cadence extreme-ultraviolet (EUV) images obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we investigate the solar sources of 26 3He-rich solar energetic particle (SEP) events at ≲1 MeV nucleon−1 that were well-observed by the Advanced Composition Explorer during solar cycle 24. Identification of the solar sources is based on the association of 3He-rich events with type III radio bursts and electron events as observed by Wind. The source locations are further verified in EUV images from the Solar and Terrestrial Relations Observatory, which provides information on solar activities in the regions not visible from the Earth. Based on AIA observations, 3He-rich events are not only associated with coronal jets as emphasized in ... [READ MORE]

Authors: Nariaki V. Nitta, Glenn M. Mason, Linghua Wang, Christina M. S. Cohen, Mark E. Wiedenbeck
Projects: ACE,SDO-AIA,SoHO-LASCO,STEREO,Wind

Publication Status: Published by the Astrophysical Journal
Last Modified: 2015-06-29 11:56
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The Localization of Particle Acceleration Sites in Solar Flares and CMEs    

Markus J. Aschwanden   Submitted: 2005-07-20 17:54

We review the particular aspect of localizing particle acceleration sites in solar flares and coronal mass ejections (CMEs). Depending on the magnetic field configuration at the particle acceleration site, distinctly different radiation signatures are produced: (1) If accelerated along compact closed magnetic field lines, they precipitate to the solar chromosphere and produce hard X-rays, gamma rays, soft X-rays, and EUV emission; (2) if injected into large-scale closed magnetic field structures, they remain temporarily confined (or trapped) and produce gyrosynchrotron emission in radio and bremsstrahlung in soft X-rays; (3) if accelerated along open field lines they produce beam-driven plasma emission with a metric starting frequency; and (4) if accelerated in a propagating ... [READ MORE]

Authors: Markus J. Aschwanden
Projects: Yohkoh-HXT,Yohkoh-SXT,TRACE

Publication Status: Space Science Reviews; and Space Science Series of ISSI, Proc. of ISSI Workshop - Solar Dynamics and its Effects on the Heliosph
Last Modified: 2005-07-20 17:54
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Coronal loop seismology using multiple transverse loop oscillation harmonics    

Tom Van Doorsselaere   Submitted: 2007-08-16 07:02

Context. TRACE observations (23/11/1998 06:35:57-06:48:43UT) in the 171 ? bandpass of an active region are studied. Coronal loop oscillations are observed after a violent disruption of the equilibrium. Aims. The oscillation properties are studied to give seismological estimates of physical quantities, such as the density scale height. Methods. A loop segment is traced during the oscillation, and the resulting time series is analysed for periodicities. Results. In the loop segment displacement, two periods are found: 435.6 ? 4.5 s and 242.7 ? 6.4 s, consistent with the periods of the fundamental and 2nd harmonic fast kink oscillation. The small uncertainties allow us to estimate the density scale height in the loop to be 109 Mm, which is about double the estimated hydrostatical value of ... [READ MORE]

Authors: T. Van Doorsselaere, V.M. Nakariakov, and E. Verwichte
Projects: TRACE

Publication Status: A&A (accepted)
Last Modified: 2007-08-16 08:36
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Theoretical Modeling for the STEREO Mission    

Markus J. Aschwanden   Submitted: 2005-09-16 16:57

We summarize the theory and modeling efforts for the STEREO mission, designed for data analysis of both the remote-sensing (SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The modeling includes the background plasma in the corona, heliosphere, and solar wind, but concentrates prominently on the dynamic phenomena associated with the initiation and propagation of coronal mass ejections (CMEs). The modeling of the CME initiation includes magnetic shearing, kink instability, filament eruption, and magnetic reconnection in the flaring lower corona. The modeling of CME propagation entails interplanetary shocks, interplanetary particle beams, solar energetic particles (SEPs), geoeffective connections, and space weather.

Authors: Aschwanden,M.J., S.K.Antiochos, J.W.Cook, R.A.Howard, J.T.Karpen, J.A.Klimchuk, N.R.Sheeley, L.A.Fisk, T.I.Gombosi, N.Lugaz, W.IV.Manchester, I.I.Roussev, T.H.Zurbuchen, L.F.Burlaga, M.L.Kaiser, C.Ng, D.V.Reames, M.J.Reiner, C.J.Farrugia, A.Galvin, M.A.Lee, J.A.Linker, Z.Mikic, P.Riley, D.Alexander, A.W.Sandman, E.DeJong, P.C.Liewer, D.Odstrcil, V.Pizzo, J.Luhmann, B.Inhester, E.Marsch, R.W.Schwenn, S.Solanki, V.M.Vasyliunas, T.Wiegelmann, J.-L.H.Bougeret, M.Maksimovic, J.-L.Steinberg, I.H.Cairns, P.A.Robinson, H.Kunow, R.Wimmer-Schweingruber, P.L.Lamy, A.Llebaria, P.Bochsler, V.Bothmer, K.Kecskemety, J.Kota, and M.Scholer
Projects: Soho-EIT,Soho-MDI,Soho-LASCO,TRACE

Publication Status: Space Science Reviews, Topical Issue on -The STEREO Instruments and Mission-, (eds. Chris T. Russell and Mike L. Kaiser), submit
Last Modified: 2005-09-16 16:57
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The Spatio-Temporal Evolution of Solar Flare Observed with AIA/SDO: Fractal Diffusion, Sub-Diffusion, or Logistic Growth ?}    

Markus J. Aschwanden   Submitted: 2012-08-07 15:05

We explore the spatio-temporal evolution of solar flares by fitting a radial expansion model $r(t)$ that consists of an exponentially growing acceleration phase, followed by a deceleration phase that is parameterized by the generalized diffusion function $r(t) propto kappa (t-t_1)^{eta/2}$, which includes the logistic growth limit ($eta=0$), sub-diffusion ($eta = 0-1$), classical diffusion ($eta=1$), super-diffusion ($eta = 1-2$), and the linear expansion limit ($eta=2$). We analyze all M and X-class flares observed with GOES and AIA/SDO during the first two years of the SDO mission, amounting to 155 events. We find that most flares operate in the sub-diffusive regime ($eta=0.53pm0.27$), which we interpret in terms of anisotropic chain reactions of intermittent magnetic ... [READ MORE]

Authors: Markus J. Aschwanden
Projects: SDO-AIA

Publication Status: ApJ Vol. 757, p.94 (2012)
Last Modified: 2012-09-11 13:42
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Solar Flare Geometries. II. The Volume Fractal Dimension    

Markus J. Aschwanden   Submitted: 2007-06-06 15:50

Based on the area fractal dimension $D_2$ of solar flares measured in Paper I, we carry out modeling of the 3D flare volume here and derive an analytical relation between the volume fractal scaling $V(L) propto L^{D_3}$ and the area fractal scaling $A(L) propto L^{D_2}$. The 3D volume model captures a flare arcade with a variable number of flare loops and its fractal structure is not isotropic, but consists of aligned 1D substructures. The analytical model predicts the scaling of the area filling factor $q_A(n_{loop})$ and volumetric filling factor $q_V(n_{loop})$ as a function of the number of loops $n_{loop}$, and allows to predict the volume filling factor $q_V(q_A)$ and volume fractal dimension $D_3(D_2)$ from the observationally measured parameters $q_A$ and $D_2$. We ... [READ MORE]

Authors: Markus J. Aschwanden and Pascal D. Aschwanden
Projects: TRACE

Publication Status: Subm. to ApJ, (June 6, 2007)
Last Modified: 2007-06-07 12:37
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Energy spectra of 3He-rich solar energetic particles associated with coronal waves    

Radoslav Bucik   Submitted: 2016-09-26 12:19

In addition to their anomalous abundances, 3He-rich solar energetic particles (SEPs) show puzzling energy spectral shapes varying from rounded forms to power laws where the later are characteristics of shock acceleration. Solar sources of these particles have been often associated with jets and narrow CMEs, which are the signatures of magnetic reconnection involving open field. Recent reports on new associations with large-scale EUV waves bring new insights on acceleration and transport of 3He-rich SEPs in the corona. We examined energy spectra for 32 3He-rich SEP events observed by ACE at L1 near solar minimum in 2007-2010 and compared the spectral shapes with solar flare signatures obtained from STEREO EUV images. We found the events with jets or brightenings tend to be associated with ... [READ MORE]

Authors: R. Bucik, D. E. Innes, G. M. Mason, M. E. Wiedenbeck
Projects: ACE

Publication Status: JPCS (in press)
Last Modified: 2016-09-27 15:38
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SDO/AIA Detection of Solar Prominence Formation within a Coronal Cavity    

Thomas Berger   Submitted: 2012-08-16 18:17

We report the first analyses of SDO/AIA observations of the formation of a quiescent polar crown prominence in a coronal cavity. The He II 304 AA (log T_{max} ~ 4.8 K) data show both the gradual disappearance of the prominence due to vertical drainage and lateral transport of plasma followed by the formation of a new prominence some 12 hours later. The formation of the prominence is preceded by the appearance of a bright emission ''cloud'' in the central region of the coronal cavity. The peak brightness of the cloud progressively shifts in time from the Fe XIV 211 AA channel, through the Fe XII 193 AA channel, to the Fe IX 171 AA channel (log T_{max} ~ 6.2, 6.1, 5.8 K, respectively) while simultaneously decreasing in altitude. Filter ratio analysis estimates the initial temperature of the ... [READ MORE]

Authors: Thomas E. Berger, Wei Liu, and B. C. Low
Projects: SDO-AIA

Publication Status: Accepted by ApJ Letters, Sept 17, 2012
Last Modified: 2012-09-19 19:22
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Non-Stationary Fast-Driven Self-Organized Criticality in Solar Flares    

Markus J Aschwanden   Submitted: 2019-09-18 13:40

The original concept of self-organized criticality (Bak et al.~1987), applied to solar flare statistics (Lu and Hamilton 1991), assumed a slow-driven and stationary flaring rate, which warrants time scale separation (between flare durations and inter-flare waiting times), it reproduces power-law distributions for flare peak fluxes and durations, but predicts an exponential waiting time distribution. In contrast to these classical assumptions we observe: (i) multiple energy dissipation episodes during most flares, (ii) violation of the principle of time scale separation, (iii) a fast-driven and non-stationary flaring rate, (iv) a power law distribution for waiting times $\Delta t$, with a slope of $\alpha_{\Delta t} \approx 2.0$, as predicted from the universal reciprocality ... [READ MORE]

Authors: Markus J. Aschwanden
Projects: SDO-AIA

Publication Status: ApJ (subm)
Last Modified: 2019-09-18 23:40
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Observations of a Quasi-Periodic Fast Propagating Magnetosonic Wave in Multi-Wavelength and Its Interaction with Other Magnetic Structures    

Yuandeng Shen   Submitted: 2013-07-31 19:11

We present an observational study of a quasi-periodic fast propagating (QFP) magnetosonic wave on 2012, April 23. The multiple wave trains were observed along an active region open loop system which has a divergence geometry. The wave trains were first observed in 171 A observations at a distance of 150 Mm from the footpoint of the guiding loop system and with a speed of 689 km/s, then they appeared in 193 A observations after their interaction with a perpendicular underlaying loop system on the path, in the meantime, the wave speed decelerated to 343 km/s quickly within a short timescale. The sudden deceleration of the wave trains and their appearance in 193 A observations caused by the interaction are interpreted through geometric effect and the density increase of the guiding loop ... [READ MORE]

Authors: Shen, Yuandeng; Liu, Yu.; Su, Jiangtao.; Li, Hui.; Zhang, Xuefei; Tian, Zhanjun; Zhao, Ruijuan; Elmhamdi, Abouazza
Projects: SDO-AIA

Publication Status: Accepted by Solar Physics
Last Modified: 2013-08-01 11:16
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The evolution of barbs on a polar crown filament observed by SDO    

Leping Li   Submitted: 2012-05-07 01:21

From August 16 to 21, 2010, a northern (~ N60) polar crown filament was observed by Solar Dynamics Observatory (SDO). Employing the six day SDO/AIA data, we identify 69 barbs, and select 58 of them, which appeared away from the western solar limb (≤ W60), as our sample. We systematically investigate the evolution of filament barbs. Three different types of apparent formation of barbs are detected, including (1) the convergence of surrounding moving plasma condensations, comprised 55.2% of our sample, (2) the flows of plasma condensations from the filament, composed 37.9%, and (3) the plasma injections from the neighboring brightening regions, comprised 6.9%. We also find three different ways of barb disappearance, involving: (i) the bi-lateral movements (44.8%), and (ii) the ... [READ MORE]

Authors: Leping Li and Jun Zhang
Projects: SDO-AIA

Publication Status: Accepted by Sol. Phys., 39 pages, 16 figures
Last Modified: 2012-05-07 13:36
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First imaging spectroscopy observations of solar drift pair bursts    

Eduard Kontar   Submitted: 2019-10-23 01:15

Drift pairs are an unusual type of fine structure sometimes observed in dynamic spectra of solar radio emission. They appear as two identical short narrowband drifting stripes separated in time; both positive and negative frequency drifts are observed. Using the Low Frequency Array (LOFAR), we report unique observations of a cluster of drift pair bursts in the frequency range of 30-70 MHz made on 12 July 2017. Spectral imaging capabilities of the instrument have allowed us for the first time to resolve the temporal and frequency evolution of the source locations and sizes at a fixed frequency and along the drifting pair components. Sources of two components of a drift pair have been imaged and found to propagate in the same direction along nearly the same trajectories. Motion of the ... [READ MORE]

Authors: Alexey Kuznetsov, Eduard Kontar
Projects: None,LOw Frequency ARray (LOFAR),Murchison Widefield Array (MWA),Nobeyama Radioheliograph,SDO-AIA

Publication Status: Astronomy & Astrophysics Letters, in press
Last Modified: 2019-10-23 13:06
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A Database of Flare Ribbon Properties from the Solar Dynamics Observatory. I. Reconnection Flux    

Maria D Kazachenko   Submitted: 2017-08-30 12:43

We present a database of 3137 solar flare ribbon events corresponding to every flare of GOES class C1.0 and greater within 45? from the central meridian, from 2010 April until 2016 April, observed by the Solar Dynamics Observatory. For every event in the database, we compare the GOES peak X-ray flux with the corresponding active region and flare ribbon properties. We find that while the peak X-ray flux is not correlated with the active region unsigned magnetic flux, it is strongly correlated with the flare ribbon reconnection flux, flare ribbon area, and the fraction of active region flux that undergoes reconnection. We find the relationship between the peak X-ray flux and the flare ribbon reconnection flux to be I_{X,peak} ~ (Φ_ribbon)^1.5. This scaling law is consistent with ... [READ MORE]

Authors: Kazachenko, Maria D.; Lynch, Benjamin J.; Welsch, Brian T.; Sun, Xudong
Projects: GOES X-rays,SDO-AIA,SDO-HMI

Publication Status: The Astrophysical Journal, Volume 845, Issue 1, article id. 49, 13 pp. (2017).
Last Modified: 2017-08-30 13:42
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The Magnetic Properties of Heating Events on High-Temperature Active Region Loops    

Ignacio Ugarte-Urra   Submitted: 2019-05-01 12:28

Understanding the relationship between the magnetic field and coronal heating is one of the central problems of solar physics. However, studies of the magnetic properties of impulsively heated loops have been rare. We present results from a study of 34 evolving coronal loops observed in the Fe XVIII line component of AIA/SDO 94 A filter images from three active regions with different magnetic conditions. We show that the peak intensity per unit cross-section of the loops depends on their individual magnetic and geometric properties. The intensity scales proportionally to the average field strength along the loop (Bavg) and inversely with the loop length (L) for a combined dependence of (Bavg/L)^0.52?0.13. These loop properties are inferred from magnetic extrapolations of the photospheric ... [READ MORE]

Authors: Ignacio Ugarte-Urra, Nicholas A. Crump, Harry P. Warren, Thomas Wiegelmann
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in The Astrophysical Journal
Last Modified: 2019-05-03 16:05
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RHESSI and SDO/AIA observations of the chromospheric and coronal plasma parameters during a solar flare    

Marina Battaglia   Submitted: 2012-10-15 01:51

X-ray and EUV observations are an important diagnostic of various plasma parameters of the solar atmosphere during solar flares. Soft X-ray and EUV observations often show coronal sources near the top of flaring loops, while hard X-ray emission is mostly observed from chromospheric footpoints. Combining RHESSI with simultaneous SDO/AIA observations, it is possible for the first time to determine the density, temperature, and emission profile of the solar atmosphere over a wide range of heights during a flare, using two independent methods. Here we analyze a near limb event during the first of three hard X-ray peaks. The emission measure, temperature, and density of the coronal source is found using soft X-ray RHESSI images while the chromospheric density is determined using RHESSI ... [READ MORE]

Authors: Marina Battaglia, Eduard P. Kontar
Projects: RHESSI,SDO-AIA

Publication Status: ApJ, accepted
Last Modified: 2012-10-15 12:44
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A Code for Automated Tracing of Coronal Loops Approaching Visual Perception    

Markus J. Aschwanden   Submitted: 2009-10-21 15:45

Here we develop a new numeric code with automated pattern recognition, customized for tracing of coronal loops, which for the first time breaks even with the results of visual tracing. The used method is based on oriented-directivity tracing of curvi-linear features, but in contrast to other general pattern recognition algorithms, it is customized to solar EUV and SXR images by taking advantage of the specific property that coronal loops have large curvature radii compared with their widths. We evaluate the performance of this new code by comparing the cumulative distribution of loop lengths, the median and maximum loop lengths, the completeness of detection, and the congruency of the detected patterns with other numeric codes and visual tracings. We find that the new code closely ... [READ MORE]

Authors: Markus J. Aschwanden
Projects: TRACE

Publication Status: Solar Physics, (in press)
Last Modified: 2010-02-19 13:50
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Relationships Between Characteristics of the Line-of-Sight Magnetic Field and Solar Flare Forecasts    

Viacheslav Sadykov   Submitted: 2017-04-12 08:57

Studying connection between solar flares and properties of magnetic field in active regions is very important for understanding the flare physics and developing space weather forecasts. In this work, we analyze relationship between the flare X-ray peak flux from the GOES satellite, and characteristics of the line-of-sight (LOS) magnetograms obtained by the SDO/HMI instrument during the period of April, 2010 - June, 2016. We try to answer two questions: 1) What characteristics of the LOS magnetic field are most important for the flare initiation and magnitude? 2) Is it possible to construct a reliable forecast of >=M1.0 and >=X1.0 class flares based only on the LOS magnetic field characteristics? To answer these questions, we apply a Polarity Inversion Line (PIL) detection algorithm, and ... [READ MORE]

Authors: Viacheslav M Sadykov, Alexander G Kosovichev
Projects: GOES X-rays,SDO-HMI

Publication Status: Submitted to the ApJ
Last Modified: 2017-04-12 17:38
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Solar Corona Loop Studies with AIA: I. Cross-Sectional Temperature Structure    

Markus J. Aschwanden   Submitted: 2011-03-01 09:31

We present a first systematic study on the cross-sectional temperature structure of coronal loops using the six coronal temperature filters of the Atmospheric Imaging Assembly (AIA) instrument on the Solar Dynamics Observatory (SDO). We analyze a sample of 100 loop snapshots measured at 10 different locations and 10 different times in active region NOAA 11089 on 2010 July 24, 21:00-22:00 UT. The cross-sectional flux profiles are measured and a cospatial background is subtracted in 6 filters in a temperature range of T ≈ 0.5-16 MK, and 4 different parameterizations of differential emission measure (DEM) distributions are fitted. We find that the reconstructed DEMs consist predominantly of narrowband peak temperature components with a thermal width of ... [READ MORE]

Authors: Markus J. Aschwanden and Paul Boerner
Projects: SDO-AIA

Publication Status: ApJ (accepted March 1, 2011; in press)
Last Modified: 2011-03-01 18:50
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The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event    

Nina Dresing   Submitted: 2012-06-08 02:03

We investigate multi-spacecraft observations of the January 17, 2010 solar energetic particle event. Energetic electrons and protons have been observed over a remarkable large longitudinal range at the two STEREO spacecraft and SOHO suggesting a longitudinal spread of nearly 360 degrees at 1,AU. The flaring active region, which was on the backside of the Sun as seen from Earth, was separated by more than 100 degrees in longitude from the magnetic footpoints of each of the three spacecraft. The event is characterized by strongly delayed energetic particle onsets with respect to the flare and only small or no anisotropies in the intensity measurements at all three locations. The presence of a coronal shock is evidenced by the observation of a type II radio burst from the Earth and ... [READ MORE]

Authors: N. Dresing, R.Gomez-Herrero, A. Klassen, B. Heber, Y. Kartavykh, W. Droege
Projects: ACE,GONG,SoHO-EIT,STEREO

Publication Status: accepted
Last Modified: 2012-06-28 04:02
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Multi-thermal representation of the kappa-distribution of solar flare electrons and application to simultaneous X-ray and EUV observations    

Marina Battaglia   Submitted: 2015-11-05 00:54

Acceleration of particles and plasma heating is one of the fundamental problems in solar flare physics. An accurate determination of the spectrum of flare energized electrons over a broad energy range is crucial for our understanding of aspects such as the acceleration mechanism and the total flare energy. Recent years have seen a growing interest in the kappa-distribution as representation of the total spectrum of flare accelerated electrons. In this work we present the kappa-distribution as a differential emission measure. This allows for inferring the electron distribution from X-ray observations and EUV observations by simultaneously fitting the proposed function to RHESSI and SDO/AIA data. This yields the spatially integrated electron spectra of a coronal source between less than 0.1 ... [READ MORE]

Authors: Marina Battaglia, Galina Motorina, Eduard P. Kontar
Projects: RHESSI,SDO-AIA

Publication Status: ApJ, accepted
Last Modified: 2015-11-05 11:05
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Energy release in the solar atmosphere from a stream of infalling prominence debris    

Andrew Inglis   Submitted: 2017-09-18 11:12

Recent high-resolution and high-cadence EUV imaging has revealed a new phenomenon, impacting prominence debris, where prominence material from failed or partial eruptions can impact the lower atmosphere, releasing energy. We report a clear example of energy release and EUV brightening due to infalling prominence debris that occurred on 2011 September 7-8. The initial eruption of material was associated with an X1.8-class flare from AR11283, occurring at 22:30 UT on 2011 September 7. Subsequently, a semi-continuous stream of this material returned to the solar surface with a velocity v > 150 km/s, impacting a region remote from the original active region between 00:20 - 00:40 UT on 2011 September 8. Using SDO/AIA, the differential emission measure of the plasma was estimated throughout ... [READ MORE]

Authors: A. R. Inglis, H. R. Gilbert and L. Ofman
Projects: SDO-AIA

Publication Status: ApJL, accepted
Last Modified: 2017-09-20 09:05
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Statistical Analysis of Torus and Kink Instabilities in Solar Eruptions    

Ju Jing   Submitted: 2018-10-02 09:14

A recent laboratory experiment of ideal magnetohydrodynamic instabilities revealed four distinct eruption regimes readily distinguished by the torus instability (TI) and helical kink instability (KI) parameters. To establish its observational counterpart, we collected 38 solar flares (stronger than GOES-class M5 in general) that took place within 45? of disk center during 2011?2017, 26 of which are associated with a halo or partial halo coronal mass ejection (CME; i.e., ejective events), while the others are CME-less (i.e., confined events). This is a complete sample of solar events satisfying our selection criteria detailed in the paper. For each event, we calculate a decay index n of the potential strapping field above the magnetic flux rope (MFR) in and around the flaring magnetic ... [READ MORE]

Authors: Ju Jing, Chang Liu, Jeongwoo Lee, Hantao Ji, Nian Liu, Yan Xu, and Haimin Wang
Projects: SDO-AIA,SDO-HMI,SoHO-LASCO

Publication Status: published in ApJ
Last Modified: 2018-10-02 10:55
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Observations of Post-flare Plasma Dynamics during an M1.0 Flare in AR11093 by SDO/AIA    

Dr. A.K. Srivastava   Submitted: 2011-10-02 21:45

We observe the motion of cool and hot plasma in a multi-stranded post flare loop system that evolved in the decay phase of a two ribbon M1.0 class flare in AR 11093 on 7 August 2010 using SDO/AIA 304 AA and 171 AA filters. The moving intensity feature and its reflected counterpart are observed in the loop system at multi-temperature. The observed hot counterpart of the plasma that probably envelopes the cool confined plasma, moves comparatively faster ($sim$34 km s$^{-1}$) to the later (29 km s$^{-1}$) in form of the spreaded intensity feature. The propagating plasma and intensity reflect from the region of another footpoint of the loop. The subsonic speed of the moving plasma and associated intensity feature may be most likely evolved in the post flare loop system through impulsive ... [READ MORE]

Authors: Abhishek K. Srivastava, K. Murawski
Projects: SDO-AIA

Publication Status: The Astrophysical Journal (ApJ)
Last Modified: 2011-10-03 11:11
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Helical Kink Instability in a Confined Solar Eruption    

Alshaimaa Hassanin   Submitted: 2016-09-09 07:47

A model for strongly writhing confined solar eruptions suggests an origin in the helical kink instability of a coronal flux rope which remains stable against the torus instability. This model is tested against the well observed filament eruption on 2002 May 27 in a parametric MHD simulation study which comprises all phases of the event. Good agreement with the essential observed properties is obtained. These include the confinement, terminal height, writhing, distortion, and dissolution of the filament, and the flare loops. The agreement is robust against variations in a representative range of parameter space. Careful comparisons with the observation data constrain the ratio of the external toroidal and poloidal field components to B_et/B_ep≈1 and the initial flux rope twist to ... [READ MORE]

Authors: Alshaimaa Hassanin and Bernhard Kliem
Projects: TRACE

Publication Status: Astrophys. J., accepted
Last Modified: 2016-09-10 13:39
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Characteristics of Sustained >100 γ-ray Emission Associated with Solar Flares    

Gerald Share   Submitted: 2017-10-28 14:08

We characterize and provide a catalog of thirty >100 MeV sustained γ-ray emission (SGRE) events observed by Fermi LAT. These events are temporally and spectrally distinct from the associated solar flares. Their spectra are consistent with decay of pions produced by >300 MeV protons and are not consistent with electron bremsstrahlung. SGRE start times range from CME onset to two hours later. Their durations range from about four minutes to twenty hours and appear to be correlated with durations of >100 MeV SEP proton events. The >300 MeV protons producing SGRE have spectra that can be fit with power laws with a mean index of ∼4 and RMS spread of 1.8. γ-ray line measurements indicate that SGRE proton spectra are steeper above 300 MeV than they are below 300 MeV. The number ... [READ MORE]

Authors: G. H. Share, R. J. Murphy, A. K. Tolbert, B. R. Dennis, S. M. White, R. A. Schwartz, and A. J. Tylka
Projects: Fermi/LAT

Publication Status: Submitted to Astrophysical Journal Supplement
Last Modified: 2017-11-01 12:23
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Endpoint Brightenings in Erupting Filaments    

Bernhard Kliem   Submitted: 2009-06-28 20:00

Two well known phenomena associated with erupting filaments are the transient coronal holes that form on each side of the filament channel and the bright post-event arcade with its expanding double row of footpoints. Here we focus on a frequently overlooked signature of filament eruptions: the spike- or fan-shaped brightenings that appear to mark the far endpoints of the filament. From a sample of non-active-region filament events observed with the Extreme-Ultraviolet Imaging Telescope on the Solar and Heliospheric Observatory, we find that these brightenings usually occur near the outer edges of the transient holes, in contrast to the post-event arcades, which define their inner edges. The endpoints are often multiple and are rooted in and around strong network flux well outside the ... [READ MORE]

Authors: Y.-M. Wang, K. Muglach, and B. Kliem
Projects: SoHO-EIT,SoHO-MDI,SoHO-LASCO

Publication Status: ApJ 699, 133 (2009)
Last Modified: 2009-06-29 09:40
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Continuum Contributions to the SDO/AIA Passbands During Solar Flares    

Ryan Milligan   Submitted: 2013-08-16 08:40

Data from the Multiple EUV Grating Spectrograph (MEGS-A) component of the Extreme Ultraviolet Experiment (EVE) onboard the Solar Dynamics Observatory (SDO) were used to quantify the contribution of continuum emission to each of the EUV channels of the Atmospheric Imaging Assembly (AIA), also on SDO, during an X-class solar flare that occurred on 2011 February 15. Both the pre-flare subtracted EVE spectra and fits to the associated free-free continuum were convolved with the AIA response functions of the seven EUV passbands at 10 s cadence throughout the course of the flare. It was found that 10-25% of the total emission in the 94A, 131A, 193A, and 335A passbands throughout the main phase of the flare was due to free-free emission. Reliable measurements could not be made for the 171A ... [READ MORE]

Authors: Ryan O. Milligan & Sarah A. McElroy
Projects: SDO-AIA,SDO-EVE

Publication Status: ApJ (Accepted)
Last Modified: 2013-08-19 09:04
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The origin of the modulation of the radio emission from the solar corona by a fast magnetoacoustic wave    

Dmitrii Kolotkov   Submitted: 2018-05-21 07:20

Observational detection of quasi-periodic drifting fine structures in a type III radio burst associated with a solar flare SOL2015-04-16T11:22, with Low Frequency Array, is presented. Although similar modulations of the type III emission have been observed before and were associated with the plasma density fluctuations, the origin of those fluctuations was unknown. Analysis of the striae of the intensity variation in the dynamic spectrum allowed us to reveal two quasi-oscillatory components. The shorter component has the apparent wavelength of $\sim2$\,Mm, phase speed of $\sim657$\,km\,s$^{-1}$, which gives the oscillation period of $\sim3$\,s, and the relative amplitude of $\sim0.35$\%. The longer component has the wavelength of $\sim12$\,Mm, and relative amplitude of $\sim5.1$\%. The ... [READ MORE]

Authors: Dmitrii Y. Kolotkov, Valery M. Nakariakov, Eduard P. Kontar
Projects: LOw Frequency ARray (LOFAR)

Publication Status: accepted for publication in ApJ
Last Modified: 2018-05-21 10:03
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Sun to 1 AU propagation and evolution of a slow streamer-blowout coronal mass ejection    

Benjamin Lynch   Submitted: 2010-03-25 00:37

We present a comprehensive analysis of the evolution of the classic, slow streamer-blowout CME of 1 June 2008 observed by the STEREO twin spacecraft to infer relevant properties of the pre-eruption source region which includes a substantial portion of the coronal helmet streamer belt. The CME was directed ∼40◦ East of the Sun-Earth line and the Heliospheric Imager observations are consistent with the CME propagating essentially radially to 1 AU. The elongation-time J-map constructed from the STEREO-A HI images tracks the arrival of two density peaks that bound the magnetic flux rope ICME seen at STEREO-B on 6 June 2008. From the STEREO-A elongation-time plots we measure the ICME flux rope radial size Rc(t) and find it well approximated by the constant ... [READ MORE]

Authors: B. J. Lynch, Y. Li, A. F. R. Thernisien, E. Robbrecht, G. H. Fisher, J. G. Luhmann, and A. Vourlidas
Projects: SoHO-MDI,SoHO-LASCO,STEREO

Publication Status: J. Geophysical Research, Vol. 115, A07106, doi:10.1029/2009JA015099
Last Modified: 2010-07-21 17:23
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Trigger of a blowout jet in a solar coronal mass ejection associated with a flare    

Shuhong Yang   Submitted: 2015-11-05 19:44

Using the multi-wavelength images and the photospheric magnetograms from the Solar Dynamics Observatory, we study the flare which was associated by the only one coronal mass ejection (CME) in active region (AR) 12192. The eruption of a filament caused a blowout jet, and then an M4.0 class flare occurred. This flare was located at the edge of AR instead of in the core region. The flare was close to the apparently "open" fields, appearing as extreme-ultraviolet structures that fan out rapidly. Due to the interaction between flare materials and "open" fields, the flare became an eruptive flare, leading to the CME. Then at the same site of the first eruption, another small filament erupted. With the high spatial and temporal resolution H? data from the New Vacuum Solar Telescope at the ... [READ MORE]

Authors: Xiaohong Li, Shuhong Yang, Huadong Chen, Ting Li, Jun Zhang
Projects: Other,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2015-11-06 10:53
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Explosive events in active region observed by IRIS and SST/CRISP    

Zhenghua Huang   Submitted: 2016-09-29 00:43

Transition-region explosive events (EEs) are characterized by non-Gaussian line profiles with enhanced wings at Doppler velocities of 50-150 km/s. They are believed to be the signature of solar phenomena that are one of the main contributors to coronal heating. The aim of this study is to investigate the link of EEs to dynamic phenomena in the transition region and chromosphere in an active region. We analyze observations simultaneously taken by the Interface Region Imaging Spectrograph (IRIS) in the Si IV 1394\AA\ line and the slit-jaw (SJ) 1400\AA\ images, and the Swedish 1-m Solar Telescope (SST) in the H$\alpha$ line. In total 24 events were found. They are associated with small-scale loop brightenings in SJ 1400\AA\ images. Only four events show a counterpart in the H$\alpha$-35 km/s ... [READ MORE]

Authors: Z. Huang, M. S. Madjarska, E. M. Scullion, L.-D. Xia, J. G. Doyle, T. Ray
Projects: IRIS, Swedish Solar telescope (SST)

Publication Status: accepted for publication in MNRAS
Last Modified: 2016-10-03 12:31
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Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind Over the Solar Poles    

Ken'ichi Fujiki   Submitted: 2019-02-28 23:15

We comparatively studied the long-term variation (1992-2017) in polar brightening observed with the Nobeyama Radioheliograph, the polar solar wind velocity with interplanetary scintillation observations at the Institute for Space-Earth Environmental Research, and the coronal hole distribution computed by potential field calculations of the solar corona using synoptic magnetogram data obtained at Kitt Peak National Solar Observatory. First, by comparing the solar wind velocity (V) and the brightness temperature (T_b) in the polar region, we found good correlation coefficients (CCs) between V and T_b in the polar regions, CC = 0.91 (0.83) for the northern (southern) polar region, and we obtained the V-T_b relationship as V =12.6 (T_b-10,667)^{1/2}+432. We also confirmed that the CC of V-T_b ... [READ MORE]

Authors: Ken'ichi Fujiki, Kiyoto Shibasaki, Seiji Yashiro, Munetoshi Tokumaru, Kazumasa Iwai, Satoshi Masuda
Projects: Nobeyama Radioheliograph

Publication Status: Solar Physics 2019 in press (DOI: 10.1007/s11207-019-1418-6)
Last Modified: 2019-03-05 12:48
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Magnetic Structure and Dynamics of the Erupting Solar Polar Crown Prominence on 2012 March 12    

Yingna Su   Submitted: 2015-05-26 20:34

We present an investigation of the polar crown prominence that erupted on 2012 March 12. This prominence is observed at the southeast limb by SDO/AIA (end-on view) and displays a quasi vertical-thread structure. Bright U-shape/horn-like structure is observed surrounding the upper portion of the prominence at 171 angstrom before the eruption and becomes more prominent during the eruption. The disk view of STEREO-B shows that this long prominence is composed of a series of vertical threads and displays a half loop-like structure during the eruption. We focus on the magnetic support of the prominence vertical threads by studying the structure and dynamics of the prominence before and during the eruption using observations from SDO and STEREO-B. We also construct a series of magnetic field ... [READ MORE]

Authors: Yingna Su, Adriaan van Ballegooijen, Patrick I. McCauley, Haisheng Ji, Katharine K. Reeves, Edward E. DeLuca
Projects: SDO-AIA

Publication Status: 2015, ApJ, accepted
Last Modified: 2015-05-27 14:14
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Automatic Detection and Tracking of Coronal Mass Ejections II: Multiscale Filtering of Coronagraph Images    

Jason P. Byrne   Submitted: 2012-06-13 13:24

Studying coronal mass ejections (CMEs) in coronagraph data can be challenging due to their diffuse structure and transient nature, and user-specific biases may be introduced through visual inspection of the images. The large amount of data available from the Solar and Heliospheric Observatory (SOHO), Solar TErrestrial RElations Observatory (STEREO), and future coronagraph missions also makes manual cataloging of CMEs tedious, and so a robust method of detection and analysis is required. This has led to the development of automated CME detection and cataloging packages such as CACTus, SEEDS, and ARTEMIS. Here, we present the development of a new CORIMP (coronal image processing) CME detection and tracking technique that overcomes many of the drawbacks of current catalogs. It works by first ... [READ MORE]

Authors: Jason P. Byrne, Huw Morgan, Shadia R. Habbal, Peter T. Gallagher
Projects: SoHO-LASCO,STEREO

Publication Status: Published
Last Modified: 2012-06-08 07:27
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Vertical oscillations of a coronal loop observed by TRACE    

Tongjiang Wang   Submitted: 2004-06-27 05:19

We report on a loop oscillation event observed by TRACE in the 195 Å bandpass at the solar limb. The difference images reveal the first evidence for vertical kink oscillations of the loop, i.e., alternately expanding and shrinking motions, in contrast to horizontal transverse loop oscillations reported before, which exhibit swaying motions. Based on the 3D geometry of the oscillating loop derived from the observation by fitting with a circular or elliptical loop model, we simulate these two kinds of global kink modes and find that only the vertical oscillations produce a signature in the difference images in agreement with the observations. We also find that the oscillating loop is associated with intensity variations. Based on the measured displacement amplitude, the simulation ... [READ MORE]

Authors: T. J. Wang and S. K. Solanki
Projects: None,TRACE

Publication Status: A&A 421, L33-L36 (2004)
Last Modified: 2004-06-27 05:19
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Quasi-Periodic Pulsations in Solar Flares    

Victor Melnikov   Submitted: 2009-07-26 06:48

Quasi-periodic pulsations (QPP) are a common feature of flaring energy releases in the solar atmosphere, observed in all bands, from radio to hard X-ray. In this review we concentrate on QPP with the periods longer than one second. Physical mechanisms responsible for the generation of long QPP split into two groups: ?load/unload? mechanisms and MHD oscillations. Load/unload mechanisms are repetitive regimes of flaring energy releases by magnetic reconnection or by other means. MHD oscillations can affect all elements of the flaring emission generation: triggering of reconnection and modulation of its rate, acceleration and dynamics of non-thermal electrons, and physical conditions in the emitting plasmas. In the case of MHD oscillations, the periodicity of QPP is determined either by the ... [READ MORE]

Authors: Nakariakov, V. M. and Melnikov, V. F.
Projects: CORONAS-F/SPIRIT,Hinode/XRT,RHESSI,SoHO-MDI,SoHO-SUMER,TRACE,Yohkoh-HXT

Publication Status: Space Science Reviews (accepted), Online First
Last Modified: 2009-07-27 10:48
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Eruption of a kink-unstable filament in active region NOAA 10696    

David R. Williams   Submitted: 2005-06-23 05:19

We present rapid-cadence Transition Region And Coronal Explorer (TRACE) observations which show evidence of a filament eruption from active region NOAA 10696, accompanied by an X2.5 flare, on 2004 November 10. The eruptive filament, which manifests as a fast coronal mass ejection some minutes later, rises as a kinking structure with an apparently exponential growth of height within TRACE's field of view. We compare the characteristics of this filament eruption with MHD numerical simulations of a kink-unstable magnetic flux rope, finding excellent qualitative agreement. We suggest that, while tether-weakening by breakout-like quadrupolar reconnection may be the release mechanism for the previously confined flux rope, the driver of the expansion is most likely the MHD helical kink ... [READ MORE]

Authors: David R. Williams, Tibor Török, Pascal Démoulin, Lidia van Driel-Gesztelyi, Bernhard Kliem
Projects: Soho-EIT,Soho-MDI,TRACE

Publication Status: ApJ Letters (accepted)
Last Modified: 2005-06-23 05:19
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Magnetic Kelvin-Helmholtz Instability at the Sun    

Claire Foullon   Submitted: 2011-01-21 00:05

Flows and instabilities play a major role in the dynamics of magnetised plasmas including the solar corona, magnetospheric and heliospheric boundaries, cometary tails and astrophysical jets. The non-linear effects, multi-scale and microphysical interactions inherent to the flow-driven instabilities are believed to play a role, e.g., in plasma entry across a discontinuity, generation of turbulence and enhanced drag. However, in order to clarify the efficiency of macroscopic instabilities in these processes, we lack proper knowledge of their overall morphological features. Here we show the first observations of the temporally and spatially resolved evolution of the magnetic Kelvin-Helmholtz instability in the solar corona. Unprecedented high-resolution imaging observations of vortices ... [READ MORE]

Authors: Foullon, C., Verwichte, E., Nakariakov, V.M., Nykyri, K. and Farrugia, C.J.
Projects: SDO-AIA

Publication Status: ApJL, accepted (20-01-2011)
Last Modified: 2011-01-21 08:46
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On Solving the Coronal Heating Problem    

James Klimchuk   Submitted: 2005-12-02 12:46

The question of what heats the solar corona remains one of the most important problems in astrophysics. Finding a definitive solution involves a number of challenging steps, beginning with an identification of the energy source and ending with a prediction of observable quantities that can be compared directly with actual observations. Critical intermediate steps include realistic modeling of both the energy release process (the conversion of magnetic stress energy or wave energy into heat) and the response of the plasma to the heating. A variety of difficult issues must be addressed: highly disparate spatial scales, physical connections between the corona and lower atmosphere, complex microphysics, and variability and dynamics. Nearly all of the coronal heating mechanisms that have ... [READ MORE]

Authors: James A. Klimchuk
Projects: Yohkoh-SXT,TRACE

Publication Status: Solar Physics (in press)
Last Modified: 2005-12-02 12:46
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Evaluation of a Selected Case of the Minimum Dissipative Rate Method for Non-Force-Free Solar Magnetic Field Extrapolation    

G. Allen Gary   Submitted: 2009-04-10 09:54

The minimum dissipative rate (MDR) method for deriving a coronal non-force-free magnetic field solution is partially evaluated. These magnetic field solutions employ a combination of three linear (constant-alpha) force-free-field solutions with one being a potential field (i.e., alpha=0). We examine the particular case of the solutions where the other two alpha?s are of equal magnitude but of opposite signs. This is motivated by studying the SOLIS vector magnetograms of AR 10987 which show a global alpha value consistent with an alpha=0 value as evaluated by (Curl B)z/Bz over the region. Typical of the current state of the observing technology, there is no definitive twist for input into the general MDR method. This suggests that the special alpha-case, of two ... [READ MORE]

Authors: G. Allen Gary
Projects: National Solar Observatory (Sac Peak)

Publication Status: submitted
Last Modified: 2009-04-11 09:44
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Turbulence, Complexity, and Solar Flares    

R.T.James McAteer   Submitted: 2009-09-30 09:42

The issue of predicting solar flares is one of the most fundamental in physics, addressing issues of plasma physics, high-energy physics, and modelling of complex systems. It also poses societal consequences, with our ever-increasing need for accurate space weather forecasts. Solar flares arise naturally as a competition between an input (flux emergence and rearrangement) in the photosphere and an output (electrical current build up and resistive dissipation) in the corona. Although initially localised, this redistribution affects neighbouring regions and an avalanche occurs resulting in large scale eruptions of plasma, particles, and magnetic field. As flares are powered from the stressed field rooted in the photosphere, a study of the photospheric magnetic complexity can be used to both ... [READ MORE]

Authors: R. T. James McAteer, Peter T. Gallagher, Paul A. Conlon
Projects: GONG,Mount Wilson Observatory,SoHO-MDI

Publication Status: Advances in Space Science Research
Last Modified: 2009-10-01 06:31
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Measurement of Vector Magnetic Field in a Flare kernel with a Spectropolarimetric Observation in He I 10830 A    

Tetsu Anan   Submitted: 2018-08-27 15:03

A flare kernel associated with a C4 class flare was observed in a spectral window including the He I triplet 10830 A and Si I 10827 A with a spectropolarimeter on the Domeless Solar Telescope at Hida Observatory on August 9th, 2015. Observed Stokes profiles of the He I triplet in the flare kernel in its post-maximum phase are well reproduced through inversions considering the Zeeman and the Paschen-Back effects with a three slab model of the flare kernel, in which two slabs having up and downward velocities produce emissions and one slab produces an absorption. The magnetic field strength inferred from the emission components of the He I line is 1400 G, which is significantly stronger than 690 G that is observed at the same location in the same line 6.5 hours before the flare. In ... [READ MORE]

Authors: Tetsu Anan, Takurou Yoneya, Kiyoshi Ichimoto, Satoru Ueno, Daikou Shiota, Satoshi Nozawa, Shinsuke Takasao, Tomoko Kawate
Projects: Domeless Solar Telescope (Hida Observatory)

Publication Status: accepted for publication in PASJ
Last Modified: 2018-08-31 12:55
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Investigating the driving mechanisms of coronal mass ejections    

Peter Gallagher   Submitted: 2010-04-07 03:20

Aims: The objective of this study was to examine the kinematics of coronal mass ejections (CMEs) using EUV and coronagraph images, and to make a quantitative comparison with a number of theoretical models. One particular aim was to investigate the acceleration profile of CMEs in the low corona. Methods: We selected two CME events for this study, which occurred on 2006 December 17 (CME06) and 2007 December 31 (CME07). CME06 was observed using the EIT and LASCO instruments on-board SOHO, while CME07 was observed using the SECCHI imaging suite on STEREO. The first step of the analysis was to track the motion of each CME front and derive its velocity and acceleration. We then compared the observational kinematics, along with the information of the associated X-ray emissions from GOES and ... [READ MORE]

Authors: Chia-Hsien Lin, Peter T. Gallagher, and Claire L. Raftery
Projects: RHESSI,SoHO-EIT,SoHO-LASCO,STEREO

Publication Status: A&A (accepted)
Last Modified: 2010-04-07 13:37
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Measurement of the Height of the Chromospheric Network Emission from Solar Dynamics Observatory Images    

Costas Alissandrakis   Submitted: 2019-11-05 09:48

We measured the height of the chromospheric network in the 1700, 1600, and 304 A wavelength bands of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) from the shift of features on the disk with respect to corresponding features in SDO/Helioseismic and Magnetic Imager (HMI) images of the absolute value of the longitudinal magnetic field. We found that near the limb the 304 A network emission forms 3.60? 0.24 Mm above the 1600 A emission, which, in turn, forms 0.48? 0.10 Mm above the HMI (6173 A) level. At the center of the disk the corresponding height differences are 2.99? 0.02 Mm and 0.39? 0.06 Mm respectively. We also found that the 1600 A network emission forms 0.25? 0.02 Mm above the 1700 A emission near the limb and 0.20? 0.02 Mm at the disk center. ... [READ MORE]

Authors: C. E. Alissandrakis
Projects: SDO-AIA,SDO-HMI

Publication Status: Acceped, Solar Physics
Last Modified: 2019-11-06 10:37
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High-Cadence and High-Resolution Halpha Imaging Spectroscopy of a Circular Flare's Remote Ribbon with IBIS    

Na Deng   Submitted: 2013-04-16 07:46

We present an unprecedented high-resolution ha imaging spectroscopic observation of a C4.1 flare taken with the Interferometric Bidimensional Spectrometer (IBIS) in conjunction with the adaptive optics system at the 76~cm Dunn Solar Telescope on 2011 October 22 in active region NOAA 11324. Such a two-dimensional spectroscopic observation covering the entire evolution of a flare ribbon with high spatial (0.1arcpix image scale), cadence (4.8~s) and spectral (0.1~AA stepsize) resolution is rarely reported. The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS. Such a circular-ribbon flare with a remote brightening is predicted in 3D fan-spine reconnection but so far has been rarely ... [READ MORE]

Authors: Na Deng, Alexandra Tritschler, Ju Jing, Xin Chen, Chang Liu, Kevin Reardon, Carsten Denker, Yan Xu, and Haimin Wang
Projects: Hinode/SOT,National Solar Observatory (Sac Peak),RHESSI,SDO-AIA,SDO-HMI

Publication Status: The Astrophysical Journal, accepted
Last Modified: 2013-04-17 12:22
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Forward Modelling of Standing Kink Modes in Coronal Loops II. Applications    

Ding Yuan   Submitted: 2016-03-08 03:34

Magnetohydrodynamic waves are believed to play a significant role in coronal heating, and could be used for remote diagnostics of solar plasma. Both the heating and diagnostic applications rely on a correct inversion (or backward modelling) of the observables into the thermal and magnetic structures of the plasma. However, owing to the limited availability of observables, this is an ill-posed issue. Forward Modelling is to establish a plausible mapping of plasma structuring into observables. In this study, we set up forward models of standing kink modes in coronal loops and simulate optically thin emissions in the extreme ultraviolet bandpasses, and then adjust plasma parameters and viewing angles to match three events of transverse loop oscillations observed by the Solar Dynamics ... [READ MORE]

Authors: Ding Yuan, Tom Van Doorsselaere
Projects: SDO-AIA

Publication Status: ApJS in press
Last Modified: 2016-03-08 12:17
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Heating and cooling of coronal loops observed by SDO    

Leping Li   Submitted: 2015-09-15 05:42

Context: One of the most prominent processes suggested to heat the corona to well above 10^6 K builds on nanoflares, short bursts of energy dissipation. Aims: We compare observations to model predictions to test the validity of the nanoflare process. Methods: Using extreme UV data from AIA/SDO and HMI/SDO line-of-sight magnetograms we study the spatial and temporal evolution of a set of loops in active region AR 11850. Results: We find a transient brightening of loops in emission from Fe xviii forming at about 7.2 MK while at the same time these loops dim in emission from lower temperatures. This points to a fast heating of the loop that goes along with evaporation of material that we observe as apparent upward motions in the image sequence. After this initial phases lasting ... [READ MORE]

Authors: Li, L. P., Peter, H., Chen, F., and Zhang, J.
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted by A&A
Last Modified: 2015-09-16 13:50
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Modeling of the sunspot-associated microwave emission using a new method of DEM inversion    

Costas Alissandrakis   Submitted: 2018-12-17 08:24

We developed a method to compute the temperature and density structure along the line of sight by inversion of the differential emission measure (DEM), under the assumptions of stratification and hydrostatic equilibrium. We applied this method to the DEM obtained from AIA observations and used the results, together with potential extrapolations of the photospheric magnetic field, to compute the microwave emission of three sunspots, which we compared with observations from the RATAN-600 radio telescope and the Nobeyama Radioheliograph (NoRH). Our DEM based models reproduced very well the observations of the moderate-size spot on October 2011 and within 25% the data of a similar sized spot on March 2016, but predicted too low values for the big spot of April 14, 2016. The latter was better ... [READ MORE]

Authors: C. E. Alissandrakis, V. M. Bogod, T. I. Kaltman, S. Patsourakos, N. G. Peterova
Projects: Nobeyama Radioheliograph,RATAN-600,SDO-AIA

Publication Status: Acceped for publication in Solar Physics
Last Modified: 2018-12-19 12:30
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Quasi-periodic pulsations with varying period in multi-wavelength observations of an x-class flare    

Jing Huang   Submitted: 2014-08-03 20:53

This work presents an interesting phenomenon of the period variation in quasi-periodic pulsations (QPPs) observed during the impulsive phase of a coronal mass ejection-related X1.1 class flare on 2012 July 6. The period of QPPs was changed from 21 s at soft X-rays (SXR) to 22?23 s at microwaves, to ∼24 s at extreme ultraviolet emissions (EUV), and to 27?32 s at metric?decimetric waves. The microwave, EUV and SXR QPPs, emitted from flare loops of different heights, were oscillating in phase. Fast kink mode oscillations were proposed to be the modulation mechanism, which may exist in a wide region in the solar atmosphere from the chromosphere to the upper corona or even to the interplanetary space. Changed parameters of flare loops through the solar atmosphere could result in ... [READ MORE]

Authors: Jing Huang, Baolin Tan, Yin Zhang, Marian Karlick?y, and Hana M?esz?arosov?a
Projects: GOES X-rays ,SDO-AIA,SDO-HMI

Publication Status: published
Last Modified: 2014-08-04 17:58
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Flare Footpoint Regions and a Surge Observed by the Hinode/EUV Imaging Spectrometer (EIS), RHESSI, and SDO/AIA    

Amir Caspi   Submitted: 2015-10-28 16:05

The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft observed flare footpoint regions coincident with a surge for a M3.7 flare observed on 25 September 2011 at N12 E33 in active region 11302. The flare was observed in spectral lines of O VI, Fe X, Fe XII, Fe XIV, Fe XV, Fe XVI, Fe XVII, Fe XXIII and Fe XXIV. The EIS observations were made coincident with hard X-ray bursts observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Overlays of the RHESSI images on the EIS raster images at different wavelengths show a spatial coincidence of features in the RHESSI images with the EIS upflow and downflow regions, as well as loop-top or near-loop-top regions. A complex array of phenomena was observed including multiple evaporation regions and the ... [READ MORE]

Authors: George A. Doschek, Harry P. Warren, Brian R. Dennis, Jeffrey W. Reep, Amir Caspi
Projects: Hinode/EIS,RHESSI,SDO-AIA

Publication Status: Published -- Doschek, G. A., Warren, H. P., Dennis, B. R., Reep, J. W., & Caspi, A. 2015, ApJ, 813, 32; DOI 10.1088/0004-637X/813/1/32
Last Modified: 2015-11-02 10:52
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Predicting Coronal Mass Ejections Using Machine Learning Methods    

Monica Bobra   Submitted: 2016-03-23 12:26

Of all the activity observed on the Sun, two of the most energetic events are flares and Coronal Mass Ejections (CMEs). Usually, solar active regions that produce large flares will also produce a CME, but this is not always true (Yashiro et al., 2005). Despite advances in numerical modeling, it is still unclear which circumstances will produce a CME (Webb & Howard, 2012). Therefore, it is worthwhile to empirically determine which features distinguish flares associated with CMEs from flares that are not. At this time, no extensive study has used physically meaningful features of active regions to distinguish between these two populations. As such, we attempt to do so by using features derived from [1] photospheric vector magnetic field data taken by the Solar Dynamics Observatory's ... [READ MORE]

Authors: Monica G. Bobra and Stathis Ilondis
Projects: GOES X-rays ,SDO-HMI,STEREO

Publication Status: Accepted for publication in the Astrophysical Journal
Last Modified: 2016-03-30 20:57
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Reconstruction of a Large-scale Pre-flare Coronal Current Sheet Associated with an Homologous X-shaped Flare    

Chaowei Jiang   Submitted: 2017-10-10 19:32

As a fundamental magnetic structure in the solar corona, electric current sheets (CSs) can form either prior to or during solar flare, and they are essential for magnetic energy dissipation in the solar corona by enabling magnetic reconnection. However static reconstruction of CS is rare, possibly due to limitation inherent in available coronal field extrapolation codes. Here we present the reconstruction of a large-scale pre-flare CS in solar active region 11967 using an MHD-relaxation model constrained by SDO/HMI vector magnetogram. The CS is found to be associated with a set of peculiar homologous flares that exhibit unique X-shaped ribbons and loops occurring in a quadrupolar magnetic configuration. This is evidenced by that the field lines traced from the CS to the photosphere form ... [READ MORE]

Authors: Chaowei Jiang, Xiaoli Yan, Xueshang Feng, Aiying Duan, Qiang Hu, Pingbing Zuo, Yi Wang
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted by ApJ
Last Modified: 2017-10-11 06:20
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Companion Event and Precursor of the X17 Flare on 28 October, 2003    

Cristina H. Mandrini   Submitted: 2006-08-31 05:27

A major two-ribbon X17 flare occurred on 28 October, 2003, starting at 11:01 UT in active region NOAA 10486. This flare was accompanied by the eruption of a filament and by one of the fastest halo coronal mass ejections registered during the October-November 2003 strong activity period. We focus on the analysis of magnetic field (SoHO/MDI), chromospheric (NainiTal Observatory and TRACE) and coronal (TRACE) data obtained before and during the 28 October event. By combining our data analysis with a model of the coronal magnetic field, we concentrate on the study of two events starting before the main flare. One of these events, evident in TRACE images around one hour prior to the main flare, involves a localized magnetic reconnection process associated with the presence of a coronal ... [READ MORE]

Authors: Mandrini, C.H., Demoulin, P., Schmieder, B., DeLuca, E.E., Pariat, E., Uddin, W.
Projects: SoHO-MDI,TRACE

Publication Status: Solar Phys. (in press)
Last Modified: 2006-08-31 10:17
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Comparing SSN Index to X-ray Flare and Coronal Mass Ejection Rates from Solar Cycles 22-24    

Lisa Winter   Submitted: 2016-05-02 18:59

The newly revised sunspot number series allows for placing historical geoeffective storms in the context of several hundred years of solar activity. Using statistical analyses of the Geostationary Operational Environmental Satellites (GOES) X-ray observations from the past ~30 years and the Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) Coronal Mass Ejection (CME) catalog (1996-present), we present sunspot-number-dependent flare and CME rates. In particular, we present X-ray flare rates as a function of sunspot number for the past three cycles. We also show that the 1-8 AA X-ray background flux is strongly correlated with sunspot number across solar cycles. Similarly, we show that the CME properties (e.g., proxies related to the CME ... [READ MORE]

Authors: Lisa M. Winter, Rick Pernak, and K.S. Balasubramaniam
Projects: GOES X-rays ,SoHO-LASCO

Publication Status: accepted to Solar Physics
Last Modified: 2016-05-04 09:22
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First Detection of Solar Flare Emission in Middle-Ultraviolet Balmer Continuum    

Marie Dominique   Submitted: 2018-10-24 01:59

We present the first detection of solar flare emission at middle-ultraviolet wavelengths around 2000 A by the channel 2 of the Large-Yield RAdiometer (LYRA) onboard the PROBA2 mission. The flare (SOL20170906) was also observed in the channel 1 of LYRA centered at the H I Lyman-α line at 1216 A, showing a clear non-thermal profile in both channels. The flare radiation in channel 2 is consistent with the hydrogen Balmer continuum emission produced by an optically thin chromospheric slab heated up to 10000 K. Simultaneous observations in channels 1 and 2 allow the separation of the line emission (primarily from the Lyman-α line) from the Balmer continuum emission. Together with the recent detection of the Balmer continuum emission in the near-ultraviolet by IRIS, the LYRA ... [READ MORE]

Authors: Marie Dominique, Andrei N. Zhukov, Petr Heinzel, Ingolf E. Dammasch, Laurence Wauters, Laurent Dolla, Sergei Shestov, Matthieu Kretzschmar, Janet Machol, Giovanni Lapenta, Werner Schmutz
Projects: PROBA2/LYRA

Publication Status: Accepted in ApJL
Last Modified: 2018-10-24 10:42
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The CME link to geomagnetic storms    

Nat Gopalswamy   Submitted: 2010-01-16 06:39

The coronal mass ejection (CME) link to geomagnetic storms stems from the southward component of the interplanetary magnetic field contained in the CME flux ropes and in the sheath between the flux rope and the CME-driven shock. A typical storm-causing CME is characterized by (i) high speed, (ii) large angular width (mostly halos and partial halos), and (iii)solar source location close to the central meridian. For CMEs originating at larger central meridian distances, the storms are mainly caused by the sheath field. Both the magnetic and energy contents of the storm-producing CMEs can be traced to the magnetic structure of active regions and the free energy stored in them.

Authors: N. Gopalswamy
Projects: SoHO-LASCO

Publication Status: In Solar and Stellar Variability: Impact on Earth and Planets, Proceedings IAU Symposium No. 264, 2009, H. Andrei, A. Kosovichev & J.-P. Rozelot, eds. (in press)
Last Modified: 2010-01-16 07:28
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February 15, 2011: sun-quakes produced by flux rope eruption    

Sergei Zharkov   Submitted: 2011-10-11 23:09

We present an analysis of the 2011 February 15 X-class solar flare, previously reported to produce the first sunquake in solar cycle 24. Using acoustic holography, we confirm the first, and report a second, weaker, seismic source associated with this flare. We find that the two sources are located at either end of a sigmoid, which indicates the presence of a flux rope. Contrary to the majority of previously reported sunquakes, the acoustic emission precedes the peak of major hard X-ray (HXR) sources by several minutes. Furthermore, the strongest HXR footpoints derived from RHESSI data are found to be located away from the seismic sources in the flare ribbons. We account for these discrepancies within the context of a phenomenological model of a flux rope eruption and accompanying ... [READ MORE]

Authors: Zharkov, S.I., Green, L.M., Matthews, S.A and Zharkova, V.V.
Projects: SDO-AIA,SDO-HMI

Publication Status: Astrophysical Journal Letters, in press
Last Modified: 2011-10-12 09:18
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Automated Detection of Oscillating Regions in the Solar Atmosphere    

Jack Ireland   Submitted: 2010-07-06 08:10

Recently observed oscillations in the solar atmosphere have been interpreted and modeled as magnetohydrodynamic wave modes. This has allowed the estimation of parameters that are otherwise hard to derive, such as the coronal magnetic-field strength. This work crucially relies on the initial detection of the oscillations, which is commonly done manually. The volume of Solar Dynamics Observatory (SDO) data will make manual detection inefficient for detecting all of the oscillating regions. An algorithm is presented which automates the detection of areas of the solar atmosphere that support spatially extended oscillations. The algorithm identifies areas in the solar atmosphere whose oscillation content is described by a single, dominant oscillation ... [READ MORE]

Authors: J. Ireland, M. S. Marsh, T. A. Kucera, C. A. Young
Projects: TRACE

Publication Status: Accepted
Last Modified: 2010-07-06 10:28
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Eruptions from solar ephemeral regions as an extension of the size distribution of coronal mass ejections    

Karel Schrijver   Submitted: 2009-12-04 18:16

Observations of the quiet solar corona in the 171A (~1MK) passband of the Transition Region and Coronal Explorer (TRACE) often show disruptions of the coronal part of small-scale ephemeral bipolar regions that resemble the phenomena associated with coronal mass ejections on much larger scales: ephemeral regions exhibit flare-like brightenings, rapidly rising filaments carrying absorbing material at chromospheric temperatures, or the temporary dimming of the surrounding corona. I analyze all available TRACE observing sequences between 1998/04/01 and 2009/09/30 with full-resolution 171A image sequences spanning a day or more within 500 arcsec of disk center, observing essentially quiet Sun with good exposures and relatively low background. Ten such data sets are identified between 2000 ... [READ MORE]

Authors: Carolus J. Schrijver
Projects: TRACE

Publication Status: In press for Astrophysical Journal
Last Modified: 2009-12-07 10:36
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On-disc Observations of Flux Rope Formation Prior to its Eruption    

Alexander James   Submitted: 2017-04-11 07:46

Coronal mass ejections (CMEs) are one of the primary manifestations of solar activity and can drive severe space weather effects. Therefore, it is vital to work towards being able to predict their occurrence. However, many aspects of CME formation and eruption remain unclear, including whether magnetic flux ropes are present before the onset of eruption and the key mechanisms that cause CMEs to occur. In this work, the pre-eruptive coronal configuration of an active region that produced an interplanetary CME with a clear magnetic flux rope structure at 1 AU is studied. A forward-S sigmoid appears in extreme-ultraviolet (EUV) data two hours before the onset of the eruption (SOL2012-06-14), which is interpreted as a signature of a right-handed flux rope that formed prior to the eruption. ... [READ MORE]

Authors: A. W. James, L. M. Green, E. Palmerio, G. Valori, H. A. S. Reid, D. Baker, D. H. Brooks, L. van Driel-Gesztelyi, E. K. J. Kilpua
Projects: GOES X-rays,Hinode/EIS,Nan?ay Radioheliograph,SDO-AIA,SDO-HMI

Publication Status: Accepted
Last Modified: 2017-04-11 23:28
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Coronal Shock Waves, EUV waves, and Their Relation to CMEs. I. Reconciliation of ''EIT waves'', Type II Radio Bursts, and Leading Edges of CMEs    

Victor Grechnev   Submitted: 2011-04-18 19:49

We show examples of excitation of coronal waves by flare-related abrupt eruptions of magnetic rope structures. The waves presumably rapidly steepened into shocks and freely propagated afterwards like decelerating blast waves that showed up as Moreton waves and EUV waves. We propose a simple quantitative description for such shock waves to reconcile their observed propagation with drift rates of metric type II bursts and kinematics of leading edges of coronal mass ejections (CMEs). Taking account of different plasma density falloffs for propagation of a wave up and along the solar surface, we demonstrate a close correspondence between drift rates of type II bursts and speeds of EUV waves, Moreton waves, and CMEs observed in a few known events.

Authors: V. V. Grechnev, A. M. Uralov, I. M. Chertok, I. V. Kuzmenko, A. N. Afanasyev, N. S. Meshalkina, S. S. Kalashnikov, Y. Kubo
Projects: TRACE

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2011-04-19 06:30
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Solar Cycle Variation of Magnetic Flux Ropes in a Quasi-Static Coronal Evolution Model    

Anthony Yeates   Submitted: 2010-03-25 04:35

The structure of electric current and magnetic helicity in the solar corona is closely linked to solar activity over the 11-year cycle, yet is poorly understood. As an alternative to traditional current-free ''potential field'' extrapolations, we investigate a model for the global coronal magnetic field which is non-potential and time-dependent, following the build-up and transport of magnetic helicity due to flux emergence and large-scale photospheric motions. This helicity concentrates into twisted magnetic flux ropes, which may lose equilibrium and be ejected. Here, we consider how the magnetic structure predicted by this model-in particular the flux ropes-varies over the solar activity cycle, based on photospheric input data from six periods of cycle 23. The number of flux ropes ... [READ MORE]

Authors: Yeates, A.R., Constable, J.A., and Martens, P.C.H.
Projects: SoHO-LASCO

Publication Status: Solar Physics (in press)
Last Modified: 2010-03-25 08:29
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An Updated View of Solar Eruptive Flares and Development of Shocks and CMEs: History of the 2006 December 13 GLE-Productive Extreme Event    

Victor Grechnev   Submitted: 2013-08-13 21:20

An extreme 2006 December 13 event marked the onset of the Hinode era being the last major flare in the solar cycle 23 observed with NoRH and NoRP. The event produced a fast CME, strong shock, and big particle event responsible for GLE70. We endeavor to clarify relations between eruptions, shock wave, and the flare, and to shed light on a debate over the origin of energetic protons. One concept relates it with flare processes. Another one associates acceleration of ions with a bow shock driven by a CME at (2-4)R_sun. The latter scenario is favored by a delayed particle release time after the flare. However, our previous studies have established that a shock wave is typically excited by an impulsively erupting magnetic rope (future CME core) during the flare rise, while the outer CME ... [READ MORE]

Authors: V. Grechnev, V. Kiselev, A. Uralov, N. Meshalkina, A. Kochanov
Projects: GOES X-rays ,Hinode/SOT,Hinode/XRT,Nobeyama Radioheliograph,RHESSI,SoHO-EIT,SoHO-MDI,SoHO-LASCO,SXI

Publication Status: Accepted for publication in PASJ
Last Modified: 2013-08-14 08:28
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AIA Multithermal Loop Analysis: First Results    

Joan Schmelz   Submitted: 2011-02-14 09:44

The Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory has state-of-the-art spatial resolution and shows the most detailed images of coronal loops ever observed. The series of coronal filters peak at different temperatures, which span the range of active regions. These features represent a significant improvement over earlier coronal imagers and make AIA ideal for multi-thermal analysis. Here we targeted a 171Å coronal loop in AR 11092 observed by AIA on 2010 August 3. Isothermal analysis using the 171-to-193 ratio gave a temperature of Log T ∼ 6.1, similar to the results of EIT and TRACE. Differential Emission Measure analysis, however, showed that the plasma was multithermal, not isothermal, with the bulk of the emission measure at Log T > 6.1. The result ... [READ MORE]

Authors: Schmelz, Kimble, Jenkins, Worley, Anderson, Pathak, Saar
Projects: SDO-AIA

Publication Status: ApJ Letters, 725, L34, 2010
Last Modified: 2011-02-14 11:04
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The formation of an inverse S-shaped active-region filament driven by sunspot motion and magnetic reconnection    

Xiaoli Yan   Submitted: 2016-09-21 04:46

We present a detailed study of the formation of an inverse S-shaped filament prior to its eruption in active region NOAA 11884 from October 31 to November 2, 2013. In the initial stage, clockwise rotation of a small positive sunspot around the main negative trailing sunspot formed a curved filament. Then the small sunspot cancelled with negative magnetic flux to create a longer active-region filament with an inverse S-shape. At the cancellation site a brightening was observed in UV and EUV images and bright material was transferred to the filament. Later the filament erupted after cancellation of two opposite polarities under the upper part of the filament. Nonlinear force-free field (NLFFF) extrapolation of vector photospheric fields suggests that the filament may have a twisted ... [READ MORE]

Authors: X.L. Yan, E.R. Priest, Q.L. Guo, Z.K. Xue, J.C. Wang, L.H. Yang
Projects: New Vacuum Solar Telescope (NVST)

Publication Status: Accepted for publication in ApJ.
Last Modified: 2016-09-21 11:19
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Hinode/EIS Spectroscopic Validation of Very Hot Plasma Imaged with the Solar Dynamics Observatory in Non-flaring Active Region Cores    

Fabio Reale   Submitted: 2012-04-27 08:52

We use coronal imaging observations with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), and Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) spectral data to explore the potential of narrowband EUV imaging data for diagnosing the presence of hot (T >~ 5 MK) coronal plasma in active regions. We analyze observations of two active regions (AR 11281, AR 11289) with simultaneous AIA imaging and EIS spectral data, including the Ca XVII line (at 192.8 A), which is one of the few lines in the EIS spectral bands sensitive to hot coronal plasma even outside flares. After careful co-alignment of the imaging and spectral data, we compare the morphology in a three-color image combining the 171, 335, and 94 A AIA spectral bands, with the image obtained for Ca XVII emission from ... [READ MORE]

Authors: Testa, P., Reale, F.
Projects: Hinode/EIS,SDO-AIA

Publication Status: ApJ Letters, 2012, 750, L10
Last Modified: 2012-04-27 09:07
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Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA    

Paul Wright   Submitted: 2017-07-21 08:11

NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has observed several small microflares in its initial solar pointings. In this paper, we present the first joint observation of a microflare with NuSTAR and Hinode/XRT on 2015 April 29 at ~11:29 UT. This microflare shows heating of material to several million Kelvin, observed in Soft X-rays (SXRs) with Hinode/XRT, and was faintly visible in Extreme Ultraviolet (EUV) with SDO/AIA. For three of the four NuSTAR observations of this region (pre-, decay, and post phases) the spectrum is well fitted by a single thermal model of 3.2-3.5 MK, but the spectrum during the impulsive phase shows additional emission up to 10 MK, emission equivalent to A0.1 GOES class. We recover the differential emission measure (DEM) using SDO/AIA, ... [READ MORE]

Authors: Paul J. Wright, Iain G. Hannah, Brian W. Grefenstette, Lindsay Glesener, S?m Krucker, Hugh S. Hudson, David M. Smith, Andrew J. Marsh, Stephen M. White, Matej Kuhar
Projects: GOES X-rays,Hinode/XRT,NuSTAR,SDO-AIA

Publication Status: ApJ (accepted)
Last Modified: 2017-07-21 21:31
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Changes in quasi-periodic variations of solar photospheric fields: precursor to the deep solar minimum in the cycle 23?    

Susanta Kumar Bisoi   Submitted: 2013-05-06 01:41

Using both wavelet and Fourier analysis, a study has been undertaken of the changes in the quasi-periodic variations in solar photospheric fields in the build-up to one of the deepest solar minima experienced in the past 100 years. This unusual and deep solar minimum occurred between solar cycles 23 and 24. The study, carried out using ground based synoptic magnetograms spanning the period 1975.14 to 2009.86, covered solar cycles 21, 22 and 23. A hemispheric asymmetry in periodicities of the photospheric fields was seen only at latitudes above 45 degree when the data was divided, based on a wavelet analysis, into two parts: one prior to 1996 and the other after 1996. Furthermore, the hemispheric asymmetry was observed to be confined to the latitude range 45 degree to 60 degree. This ... [READ MORE]

Authors: Susanta Kumar Bisoi, P. Janardhan, D. Chakrabarty, S. Ananthakrishnan, and Ankur Divekar
Projects: National Solar Observatory (Sac Peak)

Publication Status: Solar Physics (accepted for publication)
Last Modified: 2013-05-06 11:08
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The First Ground Level Enhancement Event of Solar Cycle 24: Direct Observation of Shock Formation and Particle Release Heights    

Nat Gopalswamy   Submitted: 2013-02-07 00:09

We report on the 2012 May 17 Ground Level Enhancement (GLE) event, which is the first of its kind in Solar Cycle 24. This is the first GLE event to be fully observed close to the surface by the Solar Terrestrial Relations Observatory (STEREO) mission. We determine the coronal mass ejection (CME) height at the start of the associated metric type II radio burst (i.e., shock formation height) as 1.38 Rs (from the Sun center). The CME height at the time of GLE particle release was directly measured from a STEREO image as 2.32 Rs, which agrees well with the estimation from CME kinematics. These heights are consistent with those obtained for cycle-23 GLEs using back-extrapolation. By contrasting the 2012 May 17 GLE with six other non-GLE eruptions from well-connected regions with similar or ... [READ MORE]

Authors: N. Gopalswamy, H. Xie, S. Akiyama, S. Yashiro, I. G. Usoskin, and J. M. Davila
Projects: GOES X-rays ,Neutron Monitors,SDO-AIA,SoHO-LASCO,STEREO

Publication Status: Accepted for publication, ApJL, February 6, 2013
Last Modified: 2013-02-07 00:09
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The Properties of Solar Energetic Particle Event-Associated Coronal Mass Ejections Reported in Different CME Catalogs    

Ian Richardson   Submitted: 2015-05-13 09:56

We compare estimates of the speed and width of coronal mass ejections (CMEs) in several catalogs for the CMEs associated with ~200 solar energetic particle (SEP) events in 2006-2013 that included 25 MeV protons. The catalogs used are: CDAW, CACTUS, SEEDS and CORIMP, all derived from observations by the LASCO coronagraphs on the SOHO spacecraft, the CACTUS catalog derived from the COR2 coronagraphs on the STEREO-A and -B spacecraft, and the DONKI catalog, which uses observations from SOHO and the STEREO spacecraft. We illustrate how, for this set of events, CME parameters can differ considerably in each catalog. The well-known correlation between CME speed and proton event intensity is shown to be similar for most catalogs, but this is largely because it is determined by a few large ... [READ MORE]

Authors: Ian G. Richardson, Tycho T. von Rosenvinge, Hilary V. Cane
Projects: SoHO-LASCO,STEREO

Publication Status: Accepted
Last Modified: 2015-05-13 11:34
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Radio Imaging of Shock-accelerated Electrons Associated with an Erupting Plasmoid on 2010 November 3    

Hazel Bain   Submitted: 2012-05-03 12:32

We present observations of a metric type II solar radio burst that occurred on the 3rd of November 2010 in association with an erupting plasmoid. The eruption was well observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory and the Reuven Ramaty High Energy Solar Spectroscopic Imager, while the burst occurred in the frequency range of the Nan?ay Radioheliograph (NRH). Such events, where the type II emission occurs in the NRH frequency range, allowing us to image the burst, are infrequent. Combining these data sets, we find that the type II is located ahead of the hot (~11 MK) core of the plasmoid, which is surrounded by a well-defined envelope of cool (few MK) plasma. Using two methods, we determine the propagation velocity of the shock: (1) fitting the ... [READ MORE]

Authors: Bain, H. M.; Krucker, S?m; Glesener, L.; Lin, R. P.
Projects: Nan?ay Radioheliograph,RHESSI,SDO-AIA

Publication Status: Accepted
Last Modified: 2012-05-04 15:01
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Time delays in quasi-periodic pulsations observed during the X2.2 solar flare on 2011 February 15    

Laurent Dolla   Submitted: 2012-03-28 04:54

We report observations of quasi-periodic pulsations (QPPs) during the X2.2 flare of 15 February 2011, observed simultaneously in several wavebands. We focus on fluctuations on time scale 1?30 s and find different time lags between different wavebands. During the impulsive phase, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) channels in the range 25?100 keV lead all the other channels. They are followed by the Nobeyama RadioPolarimeters at 9 and 17 GHz and the Extreme Ultra-Violet (EUV) channels of the Euv SpectroPhotometer (ESP) onboard the Solar Dynamic Observatory (SDO). The Zirconium and Aluminum filter channels of the Large Yield Radiometer (LYRA) onboard the Project for On-Board Autonomy (PROBA2) satellite and the SXR channel of ESP follow. The largest ... [READ MORE]

Authors: L. Dolla, C. Marqu?, D. B. Seaton, T. Van Doorsselaere, M. Dominique, D. Berghmans, C. Cabanas, A. De Groof, W. Schmutz, A. Verdini, M. J. West, J. Zender and A. N. Zhukov
Projects: Nobeyama Radioheliograph,PROBA2/LYRA,RHESSI,SDO-AIA,SDO-EVE

Publication Status: ApJ (published)
Last Modified: 2012-03-28 09:04
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Rapid Penumbral Decay Following Three X-Class Flares    

Haimin Wang   Submitted: 2003-11-10 12:35

We show strong evidence that penumbral segments decayed rapidly and permanently right after three X-class flares. Two of the three events occurred very recently in solar active region NOAA~10486, an X17 flare on 2003 October~28 and an X10 flare on 2003 October~29, 2003. The third X2.3 flare was observed in solar active region NOAA~9026 on 2000 June~6. The locations of penumbral decay are closely related to hard X-ray flare kernels or coincide with the central region of flare ribbons seen in extra-ultraviolet (EUV) images obtained by the Transition Region and Coronal Explorer (TRACE). We present difference images high-lighting the rapid changes between pre- and post-flare states of flaring active region, which show distinct decaying penumbral segments and neighboring umbral ... [READ MORE]

Authors: Haimin Wang, Cheng Liu, Jiong Qiu, Na Deng, Phil Goode and Carsten Denker
Projects: RHESSI,TRACE

Publication Status: Ap.J. Letters (submitted)
Last Modified: 2003-11-18 14:18
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On a small-scale EUV wave: the driving mechanism and the associated oscillating filament    

Yuandeng Shen   Submitted: 2017-11-15 18:21

We present observations of a small-scale Extreme-ultraviolet (EUV) wave that was associated with a mini-filament eruption and a GOES B1.9 micro-fare in the quiet Sun region. The initiation of the event was due to the photospheric magnetic emergence and cancellation in the eruption source region, which first caused the ejection of a small plasma ejecta, then the ejecta impacted on a nearby mini-filament and thereby led to the filament's eruption and the associated fare. During the filament eruption, an EUV wave at a speed of 182 - 317 km/s was formed ahead of an expanding coronal loop, which propagated faster than the expanding loop and showed obvious deceleration and refection during the propagation. In addition, the EUV wave further resulted in the transverse oscillation of a remote ... [READ MORE]

Authors: Yuandeng Shen, Yu Liu, Zhanjun Tian, Zhining Qu
Projects: SDO-AIA

Publication Status: Accepted by ApJ
Last Modified: 2017-11-17 14:24
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Analysis of a Coronal Mass Ejection and a Co-rotating Interaction Region as they travel from the Sun, passing Venus, Earth, Mars and Saturn    

Ailsa Prise   Submitted: 2015-04-21 07:40

During June 2010 a good alignment in the solar system between Venus, STEREO-B, Mars and Saturn provided an excellent opportunity to study the propagation of a Coronal Mass Ejection (CME) and closely occurring Co-rotating Interaction Region (CIR) from the Sun to Saturn. The CME erupted from the Sun at 01:30 UT on 20 June 2010, with v~600 km/s, as observed by STEREO-B, SDO and SOHO/LASCO. It arrived at Venus over 2 days later, some 3.5 days after a CIR is also detected here. The CIR was also observed at STEREO-B and Mars, prior to the arrival of the CME. The CME is not directed Earthward, but the CIR is detected here less than 2 days after its arrival at Mars. Around a month later, a strong compression of the Saturn magnetosphere is observed by Cassini, consistent with the scenario that the ... [READ MORE]

Authors: A. J. Prise, L. K. Harra, S. A. Matthews, C. S. Arridge, N. Achilleos
Projects: ACE,Other,SDO-AIA,SoHO-LASCO,STEREO

Publication Status: Published
Last Modified: 2015-04-21 10:44
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First Direct Measurements of Transverse Waves in Solar Polar Plumes Using SDO/AIA    

Morton Richard   Submitted: 2014-07-08 07:49

There is intense interest in determining the precise contribution of Alfv?nic waves propagating along solar structures to the problems of coronal heating and solar wind acceleration. Since the launch of SDO/AIA, it has been possible to resolve transverse oscillations in off-limb solar polar plumes and recently McIntosh et al. concluded that such waves are energetic enough to play a role in heating the corona and accelerating the fast solar wind. However, this result is based on comparisons to Monte Carlo simulations and confirmation via direct measurements is still outstanding. Thus, this Letter reports on the first direct measurements of transverse wave motions in solar polar plumes. Over a four hour period, we measure the transverse displacements, periods, and velocity amplitudes of 596 ... [READ MORE]

Authors: Thurgood, J. O., Morton, R. J. & McLaughlin, J. A.
Projects: SDO-AIA

Publication Status: Published in ApJ
Last Modified: 2014-07-08 11:55
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X-ray and UV investigation into the magnetic connectivity of a solar flare    

Hamish Reid   Submitted: 2012-10-11 07:11

We investigate the X-ray and UV emission detected by RHESSI and TRACE in the context of a solar flare on the 16th November 2002 with the goal of better understanding the evolution of the flare. We analysed the characteristics of the X-ray emission in the 12-25 and 25-50 keV energy range while we looked at the UV emission at 1600 angstrom. The flare appears to have two distinct phases of emission separated by a 25-second time delay, with the first phase being energetically more important. We found good temporal and spatial agreement between the 25-50 keV X-rays and the most intense areas of the 1600 angstrom UV emission. We also observed an extended 100-arcsecond < 25 keV source that appears coronal in nature and connects two separated UV ribbons later in the flare. Using the observational ... [READ MORE]

Authors: H. A. S. Reid, N. Vilmer, G. Aulanier, E. Pariat
Projects: RHESSI,TRACE

Publication Status: In Print
Last Modified: 2012-10-11 08:03
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Photospheric flux cancellation and associated flux rope formation and eruption    

Bernhard Kliem   Submitted: 2010-11-05 08:52

Aims: We study an evolving bipolar active region that exhibits flux cancellation at the internal polarity inversion line, the formation of a soft X-ray sigmoid along the inversion line and a coronal mass ejection. The aim is to investigate the quantity of flux cancellation that is involved in flux rope formation in the time period leading up to the eruption. Methods: The active region is studied using its extreme ultraviolet and soft X-ray emissions as it evolves from a sheared arcade to flux rope configuration. The evolution of the photospheric magnetic field is described and used to estimate how much flux is reconnected into the flux rope. Results: About one third of the active region flux cancels at the internal polarity inversion line in the 2.5 days leading up to the eruption. In ... [READ MORE]

Authors: L. M. Green, B. Kliem, A. J. Wallace
Projects: Hinode/EIS,Hinode/XRT,SoHO-MDI,SoHO-LASCO

Publication Status: Astron. Astrophys., in press
Last Modified: 2010-11-08 07:34
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Radio Imaging of a Type IVM Radio Burst on the 14th of August 2010    

Hazel M Bain   Submitted: 2014-01-30 16:08

Propagating coronal mass ejections (CMEs) are often accompanied by burst signatures in radio spectrogram data. We present Nancay Radioheliograph observations of a moving source of broadband radio emission, commonly referred to as a type IV radio burst (type IVM), which occurred in association with a CME on the 14th of August 2010. The event was well observed at extreme ultraviolet (EUV) wavelengths by SDO/AIA and PROBA2/SWAP, and by the STEREO SECCHI and SOHO LASCO white light (WL) coronagraphs. The EUV and WL observations show the type IVM source to be cospatial with the CME core. The observed spectra is well fitted by a power law with a negative slope, which is consistent with optically thin gyrosynchrotron emission. The spectrum shows no turn over at the lowest Nancay ... [READ MORE]

Authors: H. M. Bain, S. Krucker, P. Saint-Hilaire, and C. L. Raftery
Projects: Nan?ay Radioheliograph

Publication Status: Published
Last Modified: 2014-01-31 06:38
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From Solar Nanoflares to Stellar Giant Flares - Scaling Laws and Non-Implications for Coronal Heating    

Markus J. Aschwanden   Submitted: 2006-12-04 14:41

In this study we explore physical scaling laws applied to solar nanoflares, microflares, and large flares, as well as to stellar giant flares. Solar flare phenomena exhibit a fractal volume scaling, $V(L)lapprox L^{1.9}$, which explains the observed correlation $EM_p propto T_p^4$ between the total emission measure $EM_p$ and flare peak temperature $T_p$ in both solar and stellar flares. However, the detected stellar flares have higher emission measures $EM_p$ than solar flares at the same flare peak temperature $T_p$, which can be explained by a higher electron density that is caused by shorter heating scale heights $s_H/L approx 0.04-0.1$ (with respect to the flare loop length $L$). Using these scaling laws we calculate the total radiated flare energies $E_X$ and thermal flare ... [READ MORE]

Authors: Markus J. Aschwanden
Projects: TRACE

Publication Status: Advance in Space Science 39, 1867-1875 (2007), [Proc. COSPAR Meeting 2006, Beijing, China]
Last Modified: 2007-08-02 11:32
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Anisotropic Radio-Wave Scattering and the Interpretation of Solar Radio Emission Observations    

Eduard Kontar   Submitted: 2019-09-11 00:02

The observed properties (i.e., source size, source position, time duration, decay time) of solar radio emission produced through plasma processes near the local plasma frequency, and hence the interpretation of solar radio bursts, are strongly influenced by propagation effects in the inhomogeneous turbulent solar corona. In this work, a 3D stochastic description of the propagation process is presented, based on the Fokker-Planck and Langevin equations of radio-wave transport in a medium containing anisotropic electron density fluctuations. Using a numerical treatment based on this model, we investigate the characteristic source sizes and burst decay times for Type III solar radio bursts. Comparison of the simulations with the observations of solar radio bursts shows that predominantly ... [READ MORE]

Authors: Eduard P. Kontar, Xingyao Chen, Nicolina Chrysaphi, Natasha L.S. Jeffrey, A. Gordon Emslie, Vratislav Krupar, Milan Maksimovic, Mykola Gordovskyy, Philippa K. Browning
Projects: ALMA,LOw Frequency ARray (LOFAR),Murchison Widefield Array (MWA),Nan?ay Radioheliograph,Nobeyama Radioheliograph,Owens Valley Solar Array,STEREO,Very Large Array (VLA),Wind

Publication Status: accepted for publication in The Astrophysical Journal
Last Modified: 2019-09-11 04:19
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Coronal Mass Ejections Associated with Slow Long Duration Flares    

Tomasz Mrozek   Submitted: 2013-02-28 02:11

It is well known that there is temporal relationship between coronal mass ejections (CMEs) and associated flares. The duration of the acceleration phase is related to the duration of the rise phase of a flare. We investigate CMEs associated with slow long duration events (LDEs), i.e. flares with the long rising phase. We determined the relationships between flares and CMEs and analyzed the CME kinematics in detail. The parameters of the flares (GOES flux, duration of the rising phase) show strong correlations with the CME parameters (velocity, acceleration during main acceleration phase and duration of the CME acceleration phase). These correlations confirm the strong relation between slow LDEs and CMEs. We also analyzed the relation between the parameters of the CMEs, i.e. a velocity, an ... [READ MORE]

Authors: U. Bak-Steslicka, S. Kolomanski, T. Mrozek
Projects: GOES X-rays ,Other,SoHO-EIT,SoHO-LASCO,Yohkoh-SXT

Publication Status: Solar Physics, accepted
Last Modified: 2013-02-28 12:33
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A Statistical Study of Distant Consequences of Large Solar Energetic Events    

Karel Schrijver   Submitted: 2015-09-18 10:05

Large solar flares and eruptions may influence remote regions through perturbations in the outer-atmospheric magnetic field, leading to causally related events outside of the primary or triggering eruptions that are referred to as ``sympathetic events''. We quantify the occurrence of sympathetic events using the full-disk observations by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory associated with all flares of GOES class M5 or larger from 01 May 2010 through 31 December 2014. Using a superposed-epoch analysis, we find an increase in the rate of flares, filament eruptions, and substantial sprays and surges more than 20 degrees away from the primary flares within the first four hours at a significance of 1.8 standard deviations. We also find that the rate of ... [READ MORE]

Authors: C.J. Schrijver, P.A. Higgins
Projects: SDO-AIA

Publication Status: Solar Physics, in press
Last Modified: 2015-09-23 13:30
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The Extended Solar Cycle Tracked High into the Corona    

Richard Altrock   Submitted: 2012-09-12 10:55

We present observations of the extended solar cycle activity in white-light coronagraphs, and compare them with the more familiar features seen in the Fe XIV green-line corona. We show that the coronal activity zones seen in the emission corona can be tracked high into the corona. The peak latitude of the activity, which occurs near solar maximum, is found to be very similar at all heights. But we find that the equatorward drift of the activity zones is faster at greater heights, and that during the declining phase of the solar cycle, the lower branch of activity (that associated with the current cycle) disappears at about 3 R o. This implies that that during the declining phase of the cycle, the solar wind detected near Earth is likely to be dominated by the next cycle. The ... [READ MORE]

Authors: S. J. Tappin, R. C. Altrock
Projects: National Solar Observatory (Sac Peak)

Publication Status: accepted for publication in Solar Physics
Last Modified: 2012-09-13 10:54
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Earth-Affecting Coronal Mass Ejections Without Obvious Low Coronal Signatures    

Nariaki Nitta   Submitted: 2017-08-28 10:57

We present a study of the origin of coronal mass ejections (CMEs) that were not accompanied by obvious low coronal signatures (LCSs) and yet were responsible for appreciable disturbances at 1 AU. These CMEs characteristically start slowly. In several examples, extreme ultraviolet (EUV) images taken by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory reveal coronal dimming and a post eruption arcade when we make difference images with long enough temporal separations, which are commensurate with the slow initial development of the CME. Data from the EUV imager and COR coronagraphs of the Sun Earth Connection Coronal and Heliospheric Investigation onboard the Solar Terrestrial Relations Observatory, which provide limb views of Earth-bound CMEs, greatly help us limit ... [READ MORE]

Authors: Nariaki V. Nitta, Tamitha Mulligan
Projects: SDO-AIA,STEREO,Wind

Publication Status: Published, Solar Physics, 292, 125 (2017), DOI:10.1007/s11207-017-1147-7
Last Modified: 2017-08-29 09:56
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First High-resolution Spectroscopic Observations of an Erupting Prominence Within a Coronal Mass Ejection by the Interface Region Imaging Spectrograph (IRIS)    

Wei Liu   Submitted: 2015-02-18 09:56

Spectroscopic observations of prominence eruptions associated with coronal mass ejections (CMEs), although relatively rare, can provide valuable plasma and 3D geometry diagnostics. We report the first observations by the Interface Region Imaging Spectrograph (IRIS) mission of a spectacular fast CME/prominence eruption associated with an equivalent X1.6 flare on 2014 May 9. The maximum plane-of-sky and Doppler velocities of the eruption are 1200 and 460 km/s, respectively. There are two eruption components separated by ~200 km/s in Doppler velocity: a primary, bright component and a secondary, faint component, suggesting a hollow, rather than solid, cone-shaped distribution of material. The eruption involves a left-handed helical structure undergoing counter-clockwise (viewed top-down) ... [READ MORE]

Authors: Wei Liu, Bart De Pontieu, Jean-Claude Vial, Alan M. Title, Mats Carlsson, Han Uitenbroek, Takenori J. Okamoto, Thomas E. Berger, Patrick Antolin
Projects: IRIS,SDO-AIA

Publication Status: Accepted by ApJ (Feb. 15, 2015), on arxiv since 2015/02/17 - http://arxiv.org/abs/1502.04738
Last Modified: 2015-02-18 13:22
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Quiescent Reconnection Rate Between Emerging Active Regions and Preexisting Field, with Associated Heating: NOAA AR 11112,    

Lucas Tarr   Submitted: 2013-12-12 08:47

When magnetic flux emerges from beneath the photosphere it displaces the preexisting field in the corona, and a current sheet generally forms at the boundary between the old and new magnetic domains. Reconnection in the current sheet relaxes this highly stressed configuration to a lower energy state. This scenario is most familiar, and most often studied, in flares, where the flux transfer is rapid. We present here a study of steady, quiescent flux transfer occurring at a rate three orders of magnitude below that in a large flare. In particular we quantify the reconnection rate, and related energy release, occurring as new polarity emerges to form NOAA Active Region 11112 ( extsf{SOL16 October 2010T00:00:00L205C117}) within a region of preexisting flux. A bright, low lying kernel of ... [READ MORE]

Authors: Tarr, L.A., Longcope, D.W., McKenzie, D.E., and Yoshimura, K.
Projects: Hinode/XRT,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2013-12-12 11:37
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Interaction of Two Filament Channels of Different Chiralities    

Navin Chandra Joshi   Submitted: 2016-05-11 03:51

We present observations of interactions between the two filament channels of different chiralities and associated dynamics that occurred during 2014 April 18-20. While two flux ropes of different helicity with parallel axial magnetic fields can only undergo a bounce interaction when they are brought together, the observations at the first glance show that the heated plasma is moving from one filament channel to the other. The SDO/AIA 171 A observations and the PFSS magnetic field extrapolation reveal the presence of fan-spine magnetic configuration over the filament channels with a null point located above them. Three different events of filament activations, partial eruptions, and associated filament channel interactions have been observed. The activation initiated in one filament ... [READ MORE]

Authors: Navin Chandra Joshi, Boris Filippov, Brigitte Schmieder, Tetsuya Magara, Young-Jae, Moon, Wahab Uddin
Projects: GONG,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJ.
Last Modified: 2016-05-11 08:53
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Peculiar Stationary EUV Wave Fronts in the eruption on 2011 May 11    

Ramesh Chandra   Submitted: 2016-02-29 20:03

We present and interpret the observations of extreme ultraviolet (EUV) waves associated with a filament eruption on 2011 May 11.The filament eruption also produces a small B-class two ribbon flare and a coronal mass ejection (CME). The event is observed by the Solar Dynamic Observatory (SDO) with high spatio-temporal resolution data recorded by Atmospheric Imaging Assembly (AIA). As the filament erupts, we observe two types of EUV waves (slow and fast) propagating outwards. The faster EUV wave has a propagation velocity of ~ 500 km/s and the slower EUV wave has an initial velocity of ~ 120 km/s. We report for the first time that not only the slower EUV wave stops at a magnetic separatrix to form bright stationary fronts, but also the faster EUV wave transits a magnetic separatrix, leaving ... [READ MORE]

Authors: R. Chandra, P. F. Chen, A. Fulara, A. K. Srivastava, W. Uddin
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJ
Last Modified: 2016-03-01 10:07
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A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. II. CMEs, Shock Waves, and Drifting Radio Bursts    

Victor Grechnev   Submitted: 2013-08-15 00:32

We continue our study (Grechnev et al. (2013), doi:10.1007/s11207-013-0316-6; Paper I) on the 18 November 2003 geoffective event. To understand possible impact on geospace of coronal transients observed on that day, we investigated their properties from solar near-surface manifestations in extreme ultraviolet, LASCO white-light images, and dynamic radio spectra. We reconcile near-surface activity with the expansion of coronal mass ejections (CMEs) and determine their orientation relative to the earthward direction. The kinematic measurements, dynamic radio spectra, and microwave and X-ray light curves all contribute to the overall picture of the complex event and confirm an additional eruption at 08:07-08:20 UT close to the solar disk center presumed in Paper I. Unusual characteristics of ... [READ MORE]

Authors: V.V. Grechnev, A.M. Uralov, I.M. Chertok, V.A. Slemzin, B.P. Filippov, Ya.I. Egorov, V.G. Fainshtein, A.N. Afanasyev, N.P. Prestage, M. Temmer
Projects: CORONAS-F,GOES X-rays ,Other,RHESSI,SoHO-EIT,SoHO-LASCO,SXI

Publication Status: Solar Phys., accepted
Last Modified: 2013-08-15 07:53
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Observations of the Thermal and Dynamic Evolution of a Solar Microflare    

Jeffrey Brosius   Submitted: 2009-02-24 08:47

We observed a solar microflare over a wide temperature range with three instruments aboard the SOHO spacecraft (CDS, EIT, & MDI), TRACE (1600 A), GOES, and RHESSI. The microflare's properties and behavior are those of a miniature flare undergoing gentle chromospheric evaporation, likely driven by nonthermal electrons. Extreme-ultraviolet spectra were obtained at a rapid cadence (9.8 s) with CDS in stare mode that included emission lines originating from the chromosphere (temperature of formation T_m ~ 0.01 MK) and transition region (TR, ~0.1 MK), to coronal (~1 MK) and flare (T_m ~ 8 MK) temperatures. Light curves derived from the CDS spectra and TRACE images (obtained with a variable cadence ~ 34 s) reveal two precursor brightenings before the microflare. After the ... [READ MORE]

Authors: Brosius, J. W., and Holman, G. D.
Projects: RHESSI,SoHO-EIT,SoHO-MDI,SoHO-CDS,TRACE

Publication Status: ApJ, 692, 492 (2009 February 10)
Last Modified: 2009-02-25 07:56
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An Observational Test That Disproves Coronal Nanoflare Heating Models    

Markus J. Aschwanden   Submitted: 2007-08-20 16:17

All theoretical models of nanoflare heating in the solar corona predict loops with an unresolved multi-strand structure, which is in discrepancy to the quasi-isothermal cross-sections of the finest coronal loop structures observed with TRACE, which have spatially resolved widths of w ~ 1000-2000 km. We suggest to modify the theoretical models by relocating the hypothetical nanoflare events from their coronal location down to the chromosphere/transition region.

Authors: Markus J. Aschwanden
Projects: TRACE

Publication Status: ApJL, subm, 2007-Aug-20
Last Modified: 2007-08-21 08:38
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A Statistical Analysis of the Solar Phenomena Associated with Global EUV Waves    

David Long   Submitted: 2017-11-17 08:38

Solar eruptions are the most spectacular events in our solar system and are associated with many different signatures of energy release including solar flares, coronal mass ejections, global waves, radio emission and accelerated particles. Here, we apply the Coronal Pulse Identification and Tracking Algorithm (CorPITA) to the high cadence synoptic data provided by the Solar Dynamic Observatory (SDO) to identify and track global waves observed by SDO. 164 of the 362 solar flare events studied (45%) are found to have associated global waves with no waves found for the remaining 198 (55%). A clear linear relationship was found between the median initial velocity and the acceleration of the waves, with faster waves exhibiting a stronger deceleration (consistent with previous results). No ... [READ MORE]

Authors: David M. Long, Pearse Murphy, Georgina Graham, Eoin P. Carley, David P?rez-Su?rez
Projects: GOES X-rays,SDO-AIA,SoHO-LASCO,Wind

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2017-11-17 14:24
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The Magnetic Field of Active Region 11158 During the 2011 February 12-17 Flares : Differences between Photospheric Extrapolation and Coronal Forward-Fitting Methods    

Markus J. Aschwanden   Submitted: 2014-02-21 09:14

We developed a {sl coronal non-linear force-free field (COR-NLFFF)} forward-fitting code that fits an approximate {sl non-linear force-free field (NLFFF)} solution to the observed geometry of automatically traced coronal loops. In contrast to photospheric NLFFF codes, which calculate a magnetic field solution from the constraints of the transverse photospheric field, this new code uses coronal constraints instead, and this way provides important information on systematic errors of each magnetic field calculation method, as well as on the non-forcefreeness in the lower chromosphere. In this study we applied the COR-NLFFF code to active region NOAA 11158, during the time interval of 2011 Feb 12 to 17, which includes an X2.2 GOES-class flare plus 35 M and C-class flares. We ... [READ MORE]

Authors: Aschwanden, M.J., Sun, X.D., and Liu, Y.
Projects: SDO-AIA

Publication Status: The Astrophysical Journal 785, 34
Last Modified: 2014-03-25 16:21
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Erratum to ?Solar sources and geospace consequences of interplanetary magnetic clouds observed during solar cycle 23?Paper 1? [J. Atmos. Sol.-Terr. Phys. 70(2?4) (2008) 245?253]    

Nat Gopalswamy   Submitted: 2009-07-03 15:08

One of the figures (Fig. 4) in ??Solar sources and geospace consequences of interplanetary magnetic clouds observed during solar cycle 23 ? Paper 1?? by Gopalswamy et al.(2008, JASTP, Vol.70, Issues 2?4, February 2008, pp. 245?253) is incorrect because of a software error in the routine that was used to make the plot. The source positions of various magnetic cloud (MC) types are therefore not plotted correctly. Fig. 1 replaces Fig.4 in Paper 1 and is now plotted correctly.

Authors: Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Michalek, G.; Lepping, R. P.
Projects: SoHO-EIT,SoHO-LASCO

Publication Status: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 71, Issue 8-9, p. 1005-1009
Last Modified: 2009-07-04 10:28
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Modeling Coronal Response in Decaying Active Regions with Magnetic Flux Transport and Steady Heating    

Ignacio Ugarte-Urra   Submitted: 2017-08-16 13:04

We present new measurements of the dependence of the Extreme Ultraviolet radiance on the total magnetic flux in active regions as obtained from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (SDO). Using observations of nine active regions tracked along different stages of evolution, we extend the known radiance - magnetic flux power-law relationship ($I\propto\Phi^{\alpha}$) to the AIA 335 \AA\ passband, and the Fe XVIII 93.93 \AA\ spectral line in the 94 \AA\ passband. We find that the total unsigned magnetic flux divided by the polarity separation ($\Phi/D$) is a better indicator of radiance for the Fe XVIII line with a slope of $\alpha=3.22\pm0.03$. We then use these results to test our current understanding of ... [READ MORE]

Authors: Ignacio Ugarte-Urra, Harry P. Warren, Lisa A. Upton, Peter R. Young
Projects: SDO-AIA,SDO-HMI

Publication Status: ApJ (in press)
Last Modified: 2017-08-23 12:50
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Energy leakage as an attenuation mechanism for vertical kink oscillations in solar coronal wave guides    

Mag Selwa   Submitted: 2006-08-09 06:33

AIMS: We study wave leakage as a possible attenuation mechanism of coronal loop oscillations in the ideal MHD regime. METHODS: We consider impulsively generated oscillations in solar coronal magnetic wave guides such as a straight slab and a curved arcade loop. The two-dimensional numerical model we implement includes the effects of nonlinearity and line curvature on attenuation of fast magnetosonic kink waves. RESULTS: We show that these waves are more strongly attenuated in the arcade loop than in the slab and provide evidence that the curvature of magnetic field lines results in excess energy leakage. For parameters appropriate for a coronal loop the kink oscillation is too efficiently attenuated by energy leakage, suggesting that in the solar atmosphere wave leakage must be reduced ... [READ MORE]

Authors: Selwa, M.; Murawski, K.; Solanki, S.K.; Wang, T.J.
Projects: TRACE

Publication Status: A&A published
Last Modified: 2010-01-22 06:16
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EUV and Coronagraphic Observations of Coronal Mass Ejetions    

Durgesh Tripathi   Submitted: 2005-12-29 05:46

To identify the exact source regions of coronal mass ejections (CMEs) and to understand the basic physical mechanisms involved in their initiation are amongst the major challenges of modern day solar physics. The Extreme-ultraviolet Imaging Telescope (EIT) and Large Angle Spectrometric Coronagraph (LASCO) provides unique observations to study CMEs from 1.1 to 30 solar radii since its launch in December 1995. This thesis describes the basic physical properties of EUV post-eruptive arcades (PEAs) observed by EIT at 195 A and their role as tracers of source regions of CMEs. A detailed study of specific EUV PEA event led to the discovery of coronal downflow above the PEA emphasizing the importance of post-CME reconnection. For specific PEA events magnetograms taken from Michelson Doppler ... [READ MORE]

Authors: Durgesh Tripathi
Projects: Soho-EIT,Soho-MDI,Soho-LASCO

Publication Status: Published-2005
Last Modified: 2005-12-29 05:46
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The Formation and Early Evolution of a Coronal Mass Ejection and its Associated Shock Wave on 2014 January 8    

Linfeng Wan   Submitted: 2016-05-10 04:06

In this paper, we study the formation and early evolution of a limb coronal mass ejection (CME) and its associated shock wave that occurred on 2014 January 8. The extreme ultraviolet (EUV) images provided by the Atmospheric Imaging Assembly (AIA) on board \textit{Solar Dynamics Observatory} disclose that the CME first appears as a bubble-like structure. Subsequently, its expansion forms the CME and causes a quasi-circular EUV wave. Interestingly, both the CME and the wave front are clearly visible at all of the AIA EUV passbands. Through a detailed kinematical analysis, it is found that the expansion of the CME undergoes two phases: a first phase with a strong but transient lateral over-expansion followed by a second phase with a self-similar expansion. The temporal evolution of the ... [READ MORE]

Authors: Linfeng Wan, Xin Cheng, Tong Shi, Wei Su, M. D. Ding
Projects: SDO-AIA

Publication Status: Accepted by ApJ
Last Modified: 2016-05-10 13:48
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The Sun's Global Photospheric and Coronal Magnetic Fields: Observations and Models    

Anthony Yeates   Submitted: 2012-11-29 01:48

In this review, our present day understanding of the Sun's global photospheric and coronal magnetic fields is discussed from both observational and theoretical viewpoints. Firstly, the large-scale properties of photospheric magnetic fields are described, along with recent advances in photospheric magnetic flux transport models. Following this, the wide variety of theoretical models used to simulate global coronal magnetic fields are described. From this, the combined application of both magnetic flux transport simulations and coronal modeling techniques to describe the phenomena of coronal holes, the Sun's open magnetic flux and the hemispheric pattern of solar filaments is discussed. Finally, recent advances in non-eruptive global MHD models are described. While the review focuses mainly ... [READ MORE]

Authors: D. H. Mackay, A. R. Yeates
Projects: Mount Wilson Observatory,National Solar Observatory (Sac Peak)

Publication Status: Published: Living Rev. Solar Phys., 9 (2012) 6
Last Modified: 2012-12-01 23:52
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APPEARANCES AND STATISTICS OF CORONAL CAVITIES DURING THE ASCENDING PHASE OF SOLAR CYCLE 24    

Nishu Karna   Submitted: 2015-09-14 11:09

We present a survey of 429 coronal prominence cavities found between 2010 May and 2015 February using the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly limb synoptic maps. We examined correlations between each cavity's height, width, and length. Our findings showed that around 38% of the cavities were prolate, 27% oblate, and 35% circular in shape. The lengths of the cavities ranged from 0.06 to 2.9 ${R}_{\odot }$. When a cavity is longer than 1.5 ${R}_{\odot }$, it has a narrower height range (0.1?0.3 ${R}_{\odot }$), whereas when the cavity was shorter than 1.5 ${R}_{\odot }$, it had a wider height range (0.07?0.5 ${R}_{\odot }$). We find that the overall three-dimensional topology of the long, stable cavities can be characterized as a long tube with an elliptical cross ... [READ MORE]

Authors: N. Karna, W. D. Pesnell, and J. Zhang
Projects: SDO-AIA,SDO-HMI

Publication Status: Published (Sep 8, 2015)
Last Modified: 2015-09-14 16:09
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The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event    

Nina Dresing   Submitted: 2012-06-08 02:03

We investigate multi-spacecraft observations of the January 17, 2010 solar energetic particle event. Energetic electrons and protons have been observed over a remarkable large longitudinal range at the two STEREO spacecraft and SOHO suggesting a longitudinal spread of nearly 360 degrees at 1,AU. The flaring active region, which was on the backside of the Sun as seen from Earth, was separated by more than 100 degrees in longitude from the magnetic footpoints of each of the three spacecraft. The event is characterized by strongly delayed energetic particle onsets with respect to the flare and only small or no anisotropies in the intensity measurements at all three locations. The presence of a coronal shock is evidenced by the observation of a type II radio burst from the Earth and ... [READ MORE]

Authors: N. Dresing, R.Gomez-Herrero, A. Klassen, B. Heber, Y. Kartavykh, W. Dr?ge
Projects: ACE,GONG,SoHO-EIT,STEREO

Publication Status: accepted
Last Modified: 2012-06-28 03:59
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Properties of slow magnetoacoustic oscillations of solar coronal loops by multi-instrumental observations    

Valery Nakariakov   Submitted: 2019-03-05 08:52

Rapidly decaying oscillations of the thermal emission detected in the decay phase of solar and stellar flares are usually interpreted as standing or sloshing (reflecting) slow magnetoacoustic oscillations. We determine the scalings of the oscillation periods, damping times and amplitudes with the temperature, considering both standing and sloshing oscillations detected with different instruments. In addition, the time evolution of different spatial harmonics of a sloshing oscillation is considered. Parameters of slow oscillations observed in the EUV, X-ray, and microwave bands, and published in the literature, are used. The damping time of slow oscillations is found to scale almost linearly with the oscillation period, as the period to $0.87\pm 0.1$, giving the average Q-factor determined ... [READ MORE]

Authors: Nakariakov, V. M., Kosak, M. K., Kolotkov, D. Y., Anfinogentov, S. A., Kumar, P., Moon, Y.-J.
Projects: SDO-AIA

Publication Status: ApJL, accepted
Last Modified: 2019-03-05 12:47
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Automated Solar Feature Detection for Space Weather Applications    

David Perez-Suarez   Submitted: 2011-10-05 20:15

The solar surface and atmosphere are highly dynamic plasma environments, which evolve over a wide range of temporal and spatial scales. Large-scale eruptions, such as coronal mass ejections, can be accelerated to millions of kilometres per hour in a matter of minutes, making their automated detection and characterisation challenging. Additionally, there are numerous faint solar features, such as coronal holes and coronal dimmings, which are important for space weather monitoring and forecasting, but their low intensity and sometimes transient nature makes them problematic to detect using traditional image processing techniques. These difficulties are compounded by advances in ground- and space- based instrumentation, which have increased the volume of data that solar physicists are ... [READ MORE]

Authors: David Perez-Suarez, Paul A. Higgins, D. Shaun Bloomfield, R.T. James McAteer, Larisza D. Krista, Jason P. Byrne, Peter. T. Gallagher
Projects: SDO-AIA

Publication Status: Book chapter in -Applied Signal and Image Processing: Multidisciplinary Advancements- (ed. Rami Qahwaji, Roger Green and Evor L. Hines) pp. 207-225
Last Modified: 2011-10-05 20:15
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Coronal Loop Scaling Laws for Various Forms of Parallel Heat Conduction    

Eduard Kontar   Submitted: 2019-07-30 08:55

The solar atmosphere is dominated by loops of magnetic fluxes that connect the multi-million degree corona to the much cooler chromosphere. The temperature and density structure of quasi-static loops are determined by the continuous flow of energy from the hot corona to the lower solar atmosphere. Loop scaling laws provide relationships between global properties of the loop (such as the peak temperature, pressure, and length); they follow from the physical variable dependencies of various terms in the energy equation, and, hence, the form of the loop scaling law provides insight into the key physics that control the loop structure. Traditionally, scaling laws have been derived under the assumption of collision-dominated thermal conduction. Here, we examine the impact of different regimes ... [READ MORE]

Authors: Stephen J. Bradshaw, A. Gordon Emslie, N. H. Bian, and Eduard P. Kontar
Projects: Fermi/GBM,GOES X-rays,RHESSI,SDO-AIA,TRACE

Publication Status: ApJ in press
Last Modified: 2019-07-31 12:12
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Coronal hole evolution from multi-viewpoint data as input for a STEREO solar wind speed persistence model    

Manuela Temmer   Submitted: 2018-02-01 01:52

We present a concept study of a solar wind forecasting method for Earth, based on persistence modeling from STEREO in-situ measurements combined with multi-viewpoint EUV observational data. By comparing the fractional areas of coronal holes (CHs) extracted from EUV data of STEREO and SoHO/SDO, we perform an uncertainty assessment derived from changes in the CHs and apply those changes to the predicted solar wind speed profile at 1AU. We evaluate the method for the time period 2008-2012, and compare the results to a persistence model based on ACE in-situ measurements and to the STEREO persistence model without implementing the information on CH evolution. Compared to an ACE based persistence model, the performance of the STEREO persistence model which takes into account the evolution of ... [READ MORE]

Authors: M. Temmer, J. Hinterreiter, M.A. Reiss
Projects: ACE,SDO-AIA,SoHO-EIT,STEREO

Publication Status: The manuscript has been accepted for publication in the Journal of Space Weather and Space Climate (SWSC)
Last Modified: 2018-02-05 22:08
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Advances in Observing Various Coronal EUV Waves in the SDO Era and Their Seismological Applications (Invited Review)    

Wei Liu   Submitted: 2014-04-02 11:21

Global extreme ultraviolet (EUV) waves are spectacular traveling disturbances in the solar corona associated with energetic eruptions such as coronal mass ejections (CMEs) and flares. Over the past 15 years, observations from three generations of space-borne EUV telescopes have shaped our understanding of this phenomenon and at the same time led to controversy about its physical nature. Since its launch in 2010, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) has observed more than 210 global EUV waves in exquisite detail, thanks to its high spatio-temporal resolution and full-disk, wide-temperature coverage. A combination of statistical analysis of this large sample, 30 some detailed case studies, and data-driven MHD modeling, has been leading their ... [READ MORE]

Authors: Wei Liu, Leon Ofman
Projects: SDO-AIA

Publication Status: Accepted to Solar Physics (Topical Issue, "Exploring the Network of SDO Science")
Last Modified: 2014-04-02 12:11
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Simultaneous observation of a flux rope eruption and magnetic reconnection during an X-class solar flare    

Xiaoli Yan   Submitted: 2018-01-10 18:06

In this letter, we present a spectacular eruptive flare (X8.2) associated with a coronal mass ejection (CME) on 2017 September 10 at the west limb of the Sun. A flux rope eruption is followed by the inflow, the formation of a current sheet and a cusp structure, which were simultaneously observed during the occurrence of this flare. The hierarchical layers of the cusp-shaped structure are well observed in 131 \AA\ observation. The scenario that can be created from these observations is very consistent with the predictions of some eruptive models. Except for the characteristics mentioned above in the process of the flare predicted by classical eruption models, the current sheet separating into several small current sheets is also observed at the final stage of the flux rope eruption. The ... [READ MORE]

Authors: X. L. Yan, L. H. Yang, Z. K. Xue, Z. X. Mei, D. F. Kong, J. C. Wang, Q. L. Li
Projects: SDO-AIA

Publication Status: Accepted for publication in ApJL
Last Modified: 2018-01-14 00:01
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Analysis of magnetic shear in an X17 solar flare on October 28, 2003    

Yingna Su   Submitted: 2007-01-11 10:44

An X17 class (GOES soft X-ray) two-ribbon solar flare on 2003 October 28 is analyzed in order to determine the relationship between the timing of the impulsive phase of the flare and the magnetic shear change in the flaring region. EUV observations made by the Transition Region and Coronal Explorer (TRACE) show a clear decrease in the shear of the flare footpoints during the flare. The shear change stopped in the middle of the impulsive phase. The observations are interpreted in terms of the splitting of the sheared envelope field of the greatly sheared core rope during the early phase of the flare. We have also investigated the temporal correlation between the EUV emission from the brightenings observed by TRACE and the hard X-ray (HXR) emission (E > 150 keV) observed by the ... [READ MORE]

Authors: Y.N. Su, L. Golub, A.A. Van Ballegooijen, M. Gros
Projects: TRACE

Publication Status: Solar Physics, 2006, Vol 236, 325-349
Last Modified: 2007-01-11 11:56
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Rapid Fluctuations in the Lower Solar Atmosphere    

John K Lawrence   Submitted: 2011-11-23 16:01

The Rapid Oscillations in the Solar Atmosphere (ROSA) instrument reveals solar atmospheric fluctuations at high frequencies. Spectra of variations of the G-band intensity (IG) and CaII K-line intensity (IK) show correlated fluctuations above white noise to frequencies beyond 300 mHz and 50 mHz, respectively. The noise-corrected G-band spectrum for f = 28 - 326 mHz shows a power law with exponent -1.21 pm, 0.02, consistent with the presence of turbulent motions. G-band spectral power in the 25 - 100 mHz ('UHF') range is concentrated at the locations of magnetic bright points in the intergranular lanes and is highly intermittent in time. The intermittence of the UHF G-band fluctuations, shown by a positive kurtosis {kappa}, also suggests turbulence. Combining values of IG, IK, UHF power, ... [READ MORE]

Authors: J.K. Lawrence, A.C. Cadavid, D.J. Christian, D.B. Jess and M. Mathioudakis
Projects: National Solar Observatory (Sac Peak)

Publication Status: 2011 ApJ, 743, L24
Last Modified: 2011-11-24 02:52
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Quasi-periodic fast propagating magnetoacoustic waves during the magnetic reconnection between solar coronal loops    

Leping Li   Submitted: 2018-11-21 18:38

Employing Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) multi-wavelength im- ages, we have presented coronal condensations caused by magnetic reconnection between a system of open and closed solar coronal loops. In this Letter, we report the quasi-periodic fast magnetoacoustic waves propagating away from the reconnection region upward across the higher-lying open loops dur- ing the reconnection process. On 2012 January 19, reconnection between the higher-lying open loops and lower-lying closed loops took place, and two sets of newly reconnected loops formed. Thereafter, cooling and condensations of coronal plasma occurred in the magnetic dip region of higher-lying open loops. During the reconnection process, disturbances originating from the reconnection region prop- agate ... [READ MORE]

Authors: Li, L. P., Zhang, J., Peter, H., Chitta, L. P., Su, J. T., Song, H. Q., Xia, C., Hou, Y. J.
Projects: SDO-AIA

Publication Status: accepted for publication in ApJL
Last Modified: 2018-11-22 20:10
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Solar Coronal Jets: Observations, Theory, and Modeling    

Nour E. Raouafi   Submitted: 2016-07-06 15:34

Coronal jets represent important manifestations of ubiquitous solar transients, which may be the source of significant mass and energy input to the upper solar atmosphere and the solar wind. While the energy involved in a jet-like event is smaller than that of ?nominal? solar flares and coronal mass ejections (CMEs), jets share many common properties with these phenomena, in particular, the explosive magnetically driven dynamics. Studies of jets could, therefore, provide critical insight for understanding the larger, more complex drivers of the solar activity. On the other side of the size-spectrum, the study of jets could also supply important clues on the physics of transients close or at the limit of the current spatial resolution such as spicules. Furthermore, jet phenomena may hint ... [READ MORE]

Authors: N.E. Raouafi, S. Patsourakos, E. Pariat, P.R. Young, A.C. Sterling, A. Savcheva, M. Shimojo, F. Moreno-Insertis, C.R. DeVore, V. Archontis, T. T?r?k, H. Mason, W. Curdt, K. Meyer, K. Dalmasse, Y. Matsui
Projects: GOES X-rays ,Hinode/EIS,Hinode/SOT,Hinode/XRT,IRIS,Nobeyama Radioheliograph,RHESSI,SDO-AIA,SDO-HMI,SoHO-EIT,SoHO-MDI,SoHO-CDS,SoHO-LASCO,SoHO-SUMER,STEREO,TRACE,Yohkoh-HXT,Yohkoh-SXT

Publication Status: Published in Space Science Reviews. doi: 10.1007/s11214-016-0260-5
Last Modified: 2016-07-07 09:18
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Bridging the Gap: Capturing the Lyα Counterpart of a Type-II Spicule and its Heating Evolution with VAULT2.0 and IRIS Observations    

Georgios Chintzoglou   Submitted: 2018-03-11 23:32

We present results from an observing campaign in support of the VAULT2.0 sounding rocket launch on September 30, 2014. VAULT2.0 is a Lyα (1216 ?) spectroheliograph capable of providing spectroheliograms at high cadence. Lyα observations are highly complementary to the IRIS observations of the upper chromosphere and the low transition region (TR) but have previously been unavailable. The VAULT2.0 data provide new constraints on upper-chromospheric conditions for numerical models. The observing campaign was closely coordinated with the IRIS mission. Taking advantage of this simultaneous multi-wavelength coverage of target AR 12172 and by using state-of-the-art radiative-MHD simulations of spicules, we investigate in detail a type-II spicule associated with a fast (300 km ... [READ MORE]

Authors: Georgios Chintzoglou, Bart De Pontieu, Juan Mart?nez-Sykora, Tiago M.D. Pereira, Angelos Vourlidas, Samuel Tun Beltran
Projects: IRIS,SDO-AIA,SDO-HMI,Very high-Angular resolution Ultraviolet Telescope 2.0 (VAULT2)

Publication Status: Accepted for publication to the Astrophysical Journal
Last Modified: 2018-03-12 09:45
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Longitudinal Oscillations in Coronal Loops - Joint Observations with SOHO/CDS and TRACE    

Mike Marsh   Submitted: 2005-11-21 08:54

Joint Observing Program (JOP) 83 Solar and Heliospheric Observatory/Coronal Diagnostic Spectrometer (SOHO/CDS) and Transition Region and Coronal Explorer (TRACE) data is analysed for evidence of propagating intensity oscillations along loop structures in the solar corona. A propagating intensity oscillation with a minimum estimated speed of 50-195 km s is observed within a TRACE 171 Å coronal loop using a running difference method. Co-spatial and co-temporal CDS and TRACE observations of this loop are analysed using a wavelet analysis method. The TRACE data shows a propagating oscillation with a period of 300 s. This period is also observed with CDS suggesting propagating oscillations at chromospheric, transition region and coronal temperatures in the He I, O V and Mg IX lines.

Authors: Marsh, M. S.; Walsh, R. W.; de Moortel, I.; Ireland, J.
Projects: Soho-CDS,TRACE

Publication Status: Proceedings of 'SOHO 13 - Waves, Oscillations and Small-Scale Transient Events in the Solar Atmosphere: A Joint View from SOHO and TRACE'. 29 September - 3 October 2003, Palma de Mallorca, Balearic Islands, Spain (ESA SP-547, January 2004). Compiled by: H
Last Modified: 2005-11-21 08:54
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A Tiny Eruptive Filament as a Flux-Rope Progenitor and Driver of a Large-Scale CME and Wave    

Victor Grechnev   Submitted: 2016-04-04 21:36

A solar eruptive event SOL2010-06-13 observed with the \textit{Atmospheric Imaging Assembly} (AIA) of the \textit{Solar Dynamics Observatory} (SDO) has been extensively discussed in the contexts of the CME development and an associated extreme-ultraviolet (EUV) wave-like transient in terms of a shock driven by the apparent CME rim. Continuing the analysis of this event, we have revealed an erupting flux rope, studied its properties, and detected wave signatures inside the developing CME. These findings have allowed us to establish new features in the genesis of the CME and associated EUV wave and to reconcile all of the episodes into a single causally-related sequence. (1) A hot 11 MK flux rope developed from the structures initially associated with a compact filament system. The flux ... [READ MORE]

Authors: V.V. Grechnev, A.M. Uralov, A.A. Kochanov, I.V. Kuzmenko, D.V. Prosovetsky, Ya.I. Egorov, V.G. Fainshtein, L.K. Kashapova
Projects: None,GOES X-rays ,SDO-AIA,SDO-HMI,SoHO-LASCO,STEREO

Publication Status: Accepted for publication in Solar Physics. DOI: 10.1007/s11207-016-0888-z
Last Modified: 2016-04-06 08:20
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The Role of Erupting Sigmoid in Triggering a Flare with Parallel and Large-Scale Quasi-Circular Ribbons    

Navin Chandra Joshi   Submitted: 2015-09-07 21:28

In this paper, we present observations and analysis of an interesting sigmoid formation, eruption and the associated flare that occurred on 2014 April 18 using multi-wavelength data sets. We discuss the possible role of the sigmoid eruption in triggering the flare, which consists of two different set of ribbons: parallel ribbons as well as a large-scale quasi-circular ribbon. Several observational evidence and nonlinear force-free field extrapolation results show the existence of a large-scale fan-spine type magnetic configuration with a sigmoid lying under a section of the fan dome. The event can be explained with the following two phases. During the pre-flare phase, we observed the formation and appearance of sigmoid via tether-cutting reconnection between the two sets of sheared fields ... [READ MORE]

Authors: Navin Chandra Joshi, Chang Liu, Xudong Sun, Haimin Wang, Tetsuya Magara, Y.-J. Moon
Projects: RHESSI,SDO-AIA,SDO-HMI

Publication Status: Accepted for Publication in ApJ
Last Modified: 2015-09-08 05:18
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Generation of highly energetic electrons at reconnection outflow shocks during solar flares    

Alexander Warmuth   Submitted: 2008-10-01 08:33

Context: During solar flares a large amount of energy is suddenly released and partly transfered into energetic electrons. They are of special interest since a substantial part of the energy released during a flare is deposited into the energetic electrons. RHESSI observations, e.g. of the solar event on October 28, 2003, show that 10^36 electrons with energies > 20 keV are typically produced per second during large flares. They are related to a power of about 10^22 W. It is a still open question in which way so much electrons are acclerated up to high energies during a fraction of a second. Aims: Within the framework of the magnetic reconnection scenario, jets appear in the outflow region and can establish standing fast-mode shocks if they penetrate with a super-Alfvenic speed into ... [READ MORE]

Authors: G. Mann, A. Warmuth, H. Aurass
Projects: RHESSI,SoHO-EIT,TRACE

Publication Status: A&A, accepted
Last Modified: 2008-10-01 09:47
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Coronal mass ejections and space weather    

Nat Gopalswamy   Submitted: 2009-07-03 15:26

Solar energetic particles (SEPs) and geomagnetic storms are the two primary space weather consequences of coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs). I summarize the observed properties of CMEs and ICMEs, paying particular attention to those properties that determine the ability of CMEs in causing space weather. Then I provide observational details of two the central issues: (i) for producing geomagnetic storms, the solar source location and kinematics along with the magnetic field structure and intensity are important, and (ii) for SEPs, the shock-driving ability of CMEs, the Alfven speed in the ambient medium, and the connectivity to Earth are crucial parameters.

Authors: N. Gopalswamy
Projects: SoHO-EIT,SoHO-MDI,SoHO-LASCO,TRACE

Publication Status: Climate andWeather of the Sun-EarthSystem(CAWSES):SelectedPapers from the2007KyotoSymposium, Edited by T. Tsuda, R. Fujii, K. Shibata, and M. A. Geller, pp. 77?120. TERRAPUB, Tokyo, 2009.
Last Modified: 2009-07-04 10:27
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Coronal magnetic reconnection driven by CME expansion - The 2011 June 7 event    

Lidia van Driel-Gesztelyi   Submitted: 2014-06-12 03:28

Coronal mass ejections (CMEs) erupt and expand in a magnetically structured solar corona. Various indirect observational pieces of evidence have shown that the magnetic field of CMEs reconnects with surrounding magnetic fields, forming, e.g., dimming regions distant from the CME source regions. Analyzing Solar Dynamics Observatory (SDO) observations of the eruption from AR 11226 on 2011 June 7, we present the first direct evidence of coronal magnetic reconnection between the fields of two adjacent ARs during a CME. The observations are presented jointly with a data-constrained numerical simulation, demonstrating the formation/intensification of current sheets along a hyperbolic flux tube (HFT) at the interface between the CME and the neighbouring AR 11227. Reconnection resulted in the ... [READ MORE]

Authors: L. van Driel-Gesztelyi, D. Baker, T. T?r?k, E. Pariat, L.M. Green, D.R. Williams, J. Carlyle, G. Valori, P. D?moulin, B. Kliem, D. Long, S.A. Matthews, J.-M. Malherbe
Projects: SDO-AIA

Publication Status: Published in ApJ 788, 85 (2014)
Last Modified: 2014-06-12 14:54
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Particle Acceleration in Solar Flares and Escape into Interplanetary Space    

Markus J. Aschwanden   Submitted: 2005-03-01 09:38

We review the physics of particle acceleration and kinematics in solar flares under the particular aspect of their escape and propagation into interplanetary space. The topics include the magnetic topology in acceleration regions, the altitude of flare acceleration regions, evidence for bi-directional acceleration, the asymmetry of upward versus downward acceleration, and particle access to interplanetary space.

Authors: Markus J. Aschwanden
Projects: Yohkoh-HXT,Yohkoh-SXT,TRACE

Publication Status: AGU Monograph of AGU Chapman Conference ``Solar Energetic Plasmas and Particles'', Turku, Finland, 2-6 August 2004, (eds. Nat Go
Last Modified: 2005-03-01 09:40
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CME-driven shock and Type II solar radio burst band-splitting    

Nicolina Chrysaphi   Submitted: 2018-11-13 05:13

Coronal Mass Ejections (CMEs) are believed to be effective in producing shocks in the solar corona and the interplanetary space. One of the important signatures of shocks and shock acceleration are Type II solar radio bursts that drift with the shock speed and produce bands of plasma fundamental and higher harmonic radio emission. An intriguing aspect of Type II radio bursts is the occasional split of a harmonic band into thinner lanes, known as band-splitting. Here, we report a detailed imaging and spectroscopic observation of a CME-driven shock producing band-splitting in a Type II burst. Using the Low Frequency Array (LOFAR), we examine the spatial and temporal relation of the Type II burst to the associated CME event, use source imaging to calculate the apparent coronal density, and ... [READ MORE]

Authors: Chrysaphi, N., Kontar E. P., Holman, G. D., and Temmer, M.
Projects: LOw Frequency ARray (LOFAR),SDO-AIA,SoHO-LASCO

Publication Status: ApJ (in press)
Last Modified: 2018-11-14 12:12
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Flare differentially rotates sunspot on Sun's surface    

Chang Liu   Submitted: 2016-10-10 08:28

Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden flare-induced rotation of a sunspot using the unprecedented spatiotemporal resolution of the 1.6m New Solar Telescope, supplemented by magnetic data from the Solar Dynamics Observatory. It is clearly observed that the rotation is non-uniform over the sunspot: as the flare ribbon sweeps across, its different portions accelerate (up to ~50° h^{-1}) at different times corresponding to peaks of flare hard X-ray emission. The rotation may be driven by the surface Lorentz-force change ... [READ MORE]

Authors: Chang Liu, Yan Xu, Wenda Cao, Na Deng, Jeongwoo Lee, Hugh S. Hudson, Dale E. Gary, Jiasheng Wang, Ju Jing & Haimin Wang
Projects: BBSO/NST,Fermi/GBM,GOES X-rays,SDO-HMI

Publication Status: Published in Nature Communications
Last Modified: 2016-10-12 15:08
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Detection of three periodicities in a single oscillating coronal loop    

Tom Van Doorsselaere   Submitted: 2010-06-28 04:21

Context. TRACE 171 ? observations of transverse loop oscillations on May 13, 2001 have been studied by De Moortel & Brady (2007). They found hints of 3 periodicities present in this event. Aims. The aim of this article is to improve the analysis, and measure the periodicities more accurately in order to do coronal seismology. Methods. We create multiple (x, t)-slices across the loop, and determine the oscillatory parameters within those slices. We then use statistical methods to reduce the errors on the measured oscillations parameters. Results. We find two populations with a clearly distinct period. The population at the loop top has a period of 895 ? 2 s, while the population in the loop leg has a period of 452 ? 1 s. The fact that the ratio of these two periods is roughly 2 and the ... [READ MORE]

Authors: Van Doorsselaere T., Birtill D.C.C., and Evans G.R.
Projects: TRACE

Publication Status: A&A, 2009, vol. 508, pp. 1485
Last Modified: 2010-06-28 09:15
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Magnetic Evolution and the Disappearance of Sun-like Activity Cycles    

Travis Metcalfe   Submitted: 2017-08-04 15:34

After decades of effort, the solar activity cycle is exceptionally well characterized but it remains poorly understood. Pioneering work at the Mount Wilson Observatory demonstrated that other sun-like stars also show regular activity cycles, and suggested two possible relationships between the rotation rate and the length of the cycle. Neither of these relationships correctly describe the properties of the Sun, a peculiarity that demands explanation. Recent discoveries have started to shed light on this issue, suggesting that the Sun's rotation rate and magnetic field are currently in a transitional phase that occurs in all middle-aged stars. Motivated by these developments, we identify the manifestation of this magnetic transition in the best available data on stellar cycles. We propose ... [READ MORE]

Authors: Travis S. Metcalfe and Jennifer van Saders
Projects: Mount Wilson Observatory,Other

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2017-08-07 12:04
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3D MHD modeling of twisted coronal loops    

Fabio Reale   Submitted: 2016-07-20 08:01

We perform MHD modeling of a single bright coronal loop to include the interaction with a non-uniform magnetic field. The field is stressed by random footpoint rotation in the central region and its energy is dissipated into heating by growing currents through anomalous magnetic diffusivity that switches on in the corona above a current density threshold. We model an entire single magnetic flux tube, in the solar atmosphere extending from the high-beta chromosphere to the low-beta corona through the steep transition region. The magnetic field expands from the chromosphere to the corona. The maximum resolution is ~30 km. We obtain an overall evolution typical of loop models and realistic loop emission in the EUV and X-ray bands. The plasma confined in the flux tube is heated to active ... [READ MORE]

Authors: F. Reale, S. Orlando, M. Guarrasi, A. Mignone, G. Peres, A. W. Hood, E. R. Priest
Projects: Hinode/XRT,SDO-AIA

Publication Status: accepted for publication in ApJ
Last Modified: 2016-07-20 12:23
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Slipping magnetic reconnection during an X-class solar flare observed by SDO/AIA    

Jaroslav Dudik   Submitted: 2014-01-30 03:22

We present SDO/AIA observations of an eruptive X-class flare of July 12, 2012, and compare its evolution with the predictions of a 3D numerical simulation. We focus on the dynamics of flare loops that are seen to undergo slipping reconnection during the flare. In the AIA 131A observations, lower parts of 10 MK flare loops exhibit an apparent motion with velocities of several tens of km/s along the developing flare ribbons. In the early stages of the flare, flare ribbons consist of compact, localized bright transition-region emission from the footpoints of the flare loops. A DEM analysis shows that the flare loops have temperatures up to the formation of Fe XXIV. A series of very long, S-shaped loops erupt, leading to a CME observed by STEREO. The observed dynamics are compared with the ... [READ MORE]

Authors: J. Dudik, M. Janvier, G. Aulanier, G. Del Zanna, M. Karlicky, H. Mason, B. Schmieder
Projects: SDO-AIA

Publication Status: The Astrophysical Journal, accepted
Last Modified: 2014-01-30 10:51
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The Grad-Shafranov Reconstruction of Toroidal Magnetic Flux Ropes: Method Development and Benchmark Studies    

qiang hu   Submitted: 2017-03-10 09:51

We develop an approach of Grad-Shafranov (GS) reconstruction for toroidal structures in space plasmas, based on in-situ spacecraft measurements. The underlying theory is the GS equation that describes two-dimensional magnetohydrostatic equilibrium as widely applied in fusion plasmas. The geometry is such that the arbitrary cross section of the torus has rotational symmetry about the rotation axis $Z$, with a major radius $r_0$. The magnetic field configuration is thus determined by a scalar flux function $\Psi$ and a functional $F$ that is a single-variable function of $\Psi$. The algorithm is implemented through a two-step approach: i) a trial-and-error process by minimizing the residue of the functional $F(\Psi)$ to determine an optimal $Z$ axis orientation, and ii) for the chosen $Z$, ... [READ MORE]

Authors: Qiang Hu
Projects: ACE,STEREO,Wind

Publication Status: Solar Physics; under revision
Last Modified: 2017-03-14 11:47
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Relationship between EUV microflares and small-scale magnetic fields in the quiet Sun    

Fayu Jiang   Submitted: 2015-02-12 18:59

Microflares are small dynamic signatures observed in X-ray and extreme-ultraviolet channels. Because of their impulsive emission enhancements and wide distribution, they are thought to be closely related to coronal heating. By using the high resolution 171 {\AA} images from the Atmospheric Imaging Assembly and the lines-of-sight magnetograms obtained by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we trace 10794 microflares in a quiet region near the disk center with a field of view of 960 arcsec \times 1068 arcsec during 24 hr. The microflares have an occurrence rate of 4.4 \times 10^3 hr^−1 extrapolated over the whole Sun. Their average brightness, size, and lifetime are 1.7 I_0(of the quiet Sun), 9.6 Mm^2, and 3.6 min, respectively. There exists ... [READ MORE]

Authors: Fayu Jiang, Jun Zhang, Shuhong Yang
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in Publications of the Astronomical Society of Japan
Last Modified: 2015-02-14 22:11
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The 26 December 2001 Solar Eruptive Event Responsible for GLE63. III. CME, Shock Waves, and Energetic Particles    

Valentin Kiselev   Submitted: 2016-12-13 22:32

The 26 December 2001 moderate solar eruptive event (GOES importance M7.1, microwaves up to 4000 sfu at 9.4 GHz, CME speed 1446 km/s) produced strong fluxes of solar energetic particles (SEPs) and ground-level enhancement of cosmic-ray intensity (GLE63). To find a possible reason for the atypically high proton outcome of this event, we study its multi-wavelength images and dynamic radio spectra, and quantitatively reconcile the findings with each other. An additional eruption probably occurred in the same active region about half an hour before the main eruption, which produced two blast-wave-like shocks during the impulsive phase. Later on, the two shock waves merged around the frontal direction into a single shock, which is traced up to 25 solar radii as a halo ahead of the expanding CME ... [READ MORE]

Authors: Grechnev, V. V., Kiselev, V. I., Uralov, A. M., Klein, K.-L., Kochanov, A.A.
Projects: GOES Particles,GOES X-rays,Nobeyama Radioheliograph,SoHO-EIT,SoHO-LASCO,TRACE,Wind

Publication Status: Solar Physics, submitted
Last Modified: 2016-12-14 13:56
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High-Energy Aspects of Solar Flares: Overview of the Volume    

Amir Caspi   Submitted: 2011-10-28 12:13

In this introductory chapter, we provide a brief summary of the successes and remaining challenges in understanding the solar flare phenomenon and its attendant implications for particle acceleration mechanisms in astrophysical plasmas. We also provide a brief overview of the contents of the other chapters in this volume, with particular reference to the well-observed flare of 2002 July 23

Authors: Brian R. Dennis, A. Gordon Emslie, Hugh S. Hudson
Projects: GONG,Hinode/EIS,Hinode/SOT,Hinode/XRT,Nobeyama Radioheliograph,Owens Valley Solar Array,RHESSI,SDO-AIA,SDO-HMI,SDO-EVE,SoHO-EIT,SoHO-MDI,SoHO-CDS,SoHO-LASCO,SoHO-SUMER,STEREO,TRACE

Publication Status: Published -- Dennis, B. R., et al. 2011, Space Sci. Rev., 159, 3; DOI 10.1007/s11214-011-9802-z
Last Modified: 2011-11-17 14:17
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On a Coronal Blowout Jet: The First Observation of a Simultaneously Produced Bubble-like CME and a Jet-like CME in a Solar Event    

Yuandeng Shen   Submitted: 2012-05-01 20:06

The coronal blowout jet is a peculiar category among various jet phenomena, in which the sheared base arch, often carrying a small filament, experiences a miniature version of blowout eruption that produces large-scale coronal mass ejection (CME). In this paper, we report such a coronal blowout jet with high-resolution multi-wavelength and multi-angle observations taken from Solar Dynamics Observatory, Solar Terrestrial Relations Observatory, and Big Bear Solar Observatory. For the first time, we find that simultaneous bubble-like and jet-like CMEs were dynamically related to the blowout jet that showed cool and hot components next to each other. Our observational results indicate that (1) the cool component resulted from the eruption of the filament contained within the jet's base arch, ... [READ MORE]

Authors: Yuandeng Shen, Yu Liu, Jiangtao Su, and Yuanyong Deng
Projects: SDO-AIA

Publication Status: It has been published by ApJ (2012, ApJ, 745, 164).
Last Modified: 2012-05-02 11:15
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Quasi-periodic Pulsations in a Solar Microflare    

Valery Nakariakov   Submitted: 2018-06-07 11:07

Irregular time evolution of the radio emission generated in a B2-class microflare (SOL2017-01-25T10:15), occurring on 2017 January 25 in active region 12,628, is studied. The microflare was apparently initiated by an appearance of an s-shaped loop, observed in the EUV band. The radio emission is associated with the nonthermal electrons detected with Ramaty High Energy Solar Spectroscopic Imager, and originates simultaneously from two opposite footpoints of a magnetic fan structure beginning at a sunspot. According to the active region geometry, the footpoints are situated in the meridional direction, and hence are observed by RATAN-600 simultaneously. The radio emission intensity signal, as well as the left-hand and right-hand circular polarization signals in the low-frequency band (3-4 ... [READ MORE]

Authors: Nakariakov, V. M., Anfinogentov, S., Storozhenko, A. A., Kurochkin, E. A., Bogod, V. M., Sharykin, I. N., Kaltman, T. I.
Projects: RATAN-600

Publication Status: ApJ 859:154, 2018
Last Modified: 2018-06-07 12:36
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Using Coronal Loops to Reconstruct the Magnetic Field of an Active Region Before and After a Major Flare    

Anna Malanushenko   Submitted: 2013-12-18 16:37

The shapes of solar coronal loops are sensitive to the presence of electrical currents that are the carriers of the nonpotential energy available for impulsive activity. We use this information in a new method for modeling the coronal magnetic field of AR 11158 as a nonlinear force-free field (NLFFF). The observations used are coronal images around time of major flare activity on 2011/02/15, together with the surface line-of-sight magnetic field measurements. The data are from the Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly (HMI and AIA, respectively) onboard the Solar Dynamics Observatory (SDO). The model fields are constrained to approximate the coronal loop configurations as closely as possible, while also subject to the force-free constraints. The method does not ... [READ MORE]

Authors: A. Malanushenko, C. Schrijver, M. L. DeRosa, M. S. Wheatland
Projects: SDO-AIA,SDO-HMI

Publication Status: ApJ (accepted)
Last Modified: 2013-12-19 07:43
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Three-dimensional reconstruction of CME-driven shock-streamer interaction from radio observations: a different take on the diagnostics of coronal magnetic fields    

Salvatore Mancuso   Submitted: 2019-03-19 03:02

On 2014 October 30, a band-splitted type II radio burst associated with a coronal mass ejection (CME) observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) occurred over the southeast limb of the Sun. The fast expansion in all directions of the plasma front acted as a piston and drove a spherical fast shock ahead of it, whose outward progression was traced by simultaneous images obtained with the Nancay Radioheliograph(NRH). The geometry of the CME/shock event was recovered through 3D modeling, given the absence of concomitant stereoscopic observations, and assuming that the band-splitted type II burst was emitted at the intersection of the shock surface with two adjacent low-Alfven speed coronal streamers. From the derived spatiotemporal ... [READ MORE]

Authors: S. Mancuso, F. Frassati, A. Bemporad, D. Barghini
Projects: MLSO Mk4 K-Coronameter,Nan?ay Radioheliograph,SDO-AIA

Publication Status: A&A Letter, in press
Last Modified: 2019-03-19 10:44
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Observing the Sun with Atacama Large Millimeter/submillimeter Array (ALMA): High Resolution Interferometric Imaging    

Masumi Shimojo   Submitted: 2017-05-22 02:18

Observations of the Sun at millimeter and submillimeter wavelengths offer a unique probe into the structure, dynamics, and heating of the chromosphere; the structure of sunspots; the formation and eruption of prominences and filaments; and energetic phenomena such as jets and flares. High-resolution observations of the Sun at millimeter and submillimeter wavelengths are challenging due to the intense, extended, low- contrast, and dynamic nature of emission from the quiet Sun, and the extremely intense and variable nature of emissions associated with energetic phenomena. The Atacama Large Millimeter/submillimeter Array (ALMA) was designed with solar observations in mind. The requirements for solar observations are significantly different from observations of sidereal sources and special ... [READ MORE]

Authors: M. Shimojo, T.S. Bastian, A.S. Hales, S.M. White, K. Iwai, R.E. Hills, A. Hirota, N.M. Phillips, T. Sawada, P. Yagoubov, G. Siringo, S. Asayama, M. Sugimoto, R. Brajsa, I. Skokic, M. Barta, S. Kim, I. de Gregorio, S.A. Corder, H.S. Hudson, S. Wedemeyer, D.E. Gary, B. De Pontieu, M. Loukitcheva, G.D. Fleishman, B. Chen, A. Kobelski, Y. Yan
Projects: ALMA

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2017-05-24 14:23
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Formation of a White-Light Jet within a Quadrupolar Magnetic Configuration    

Boris Filippov   Submitted: 2011-11-29 03:52

We analyze multi-wavelength and multi-viewpoint observations of a large-scale event viewed on 7 April 2011 originating from an active region complex. The activity leads to a white-light jet being formed in the outer corona. The topology and evolution of the coronal structures were imaged in high resolution using the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). In addition, large field-of-view images of the corona were obtained using the Sun Watcher using Active Pixel System detector and Image Processing (SWAP) telescope onboard the PRoject for Onboard Autonomy (PROBA2) microsatellite, providing evidence for the connectivity of the coronal structures with outer coronal features that were imaged with the Large Angle Spectrometric Coronagraph (LASCO) C2 ... [READ MORE]

Authors: Boris Filippov, Serge Koutchmy, and Ehsan Tavabi
Projects: SDO-AIA

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2011-11-30 08:16
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Scaling Laws for Solar and Stellar Flares    

Markus J. Aschwanden   Submitted: 2006-12-19 16:34

In this study we compile for the first time comprehensive data sets of solar and stellar flare parameters, including flare peak temperatures $T_p$, flare peak volume emission measures $EM_p$, and flare durations $ au_f$ from both solar and stellar data, as well as flare length scales $L$ from solar data. Key results are that both the solar and stellar data are consistent with a common scaling law of $EM_p propto T_p^4$, but the stellar data exhibit a $approx 250$ times higher emission measure (at the same flare peak temperature). We apply the classical RTV scaling law and the generalized Serio scaling law to both the solar and stellar data. The major findings are: (1) The flare volume has a (non-Euclidian) fractal scaling of $V(L) propto L^{D_V}$ with $D_V=2.0pm0.1$, (2) Serio's ... [READ MORE]

Authors: Markus J. Aschwanden, Robert A. Stern, & Manuel Guedel
Projects: TRACE

Publication Status: ApJ (subm) - Dec 2006
Last Modified: 2006-12-20 11:35
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Plasma diagnostics of coronal dimming events    

Astrid Veronig   Submitted: 2018-02-27 04:58

Coronal mass ejections (CMEs) are often associated with coronal dimmings, i.e. transient dark regions that are most distinctly observed in Extreme Ultra-violet (EUV) wavelengths. Using Atmospheric Imaging Assembly (AIA) data, we apply Differential Emission Measure (DEM) diagnostics to study the plasma characteristics of six coronal dimming events. In the core dimming region, we find a steep and impulsive decrease of density with values up to 50-70%. Five of the events also reveal an associated drop in temperature of 5-25%. The secondary dimming regions also show a distinct decrease in density, but less strong, decreasing by 10-45%. In both the core and the secondary dimming the density changes are much larger than the temperature changes, confirming that the dimming regions are mainly ... [READ MORE]

Authors: Kamalam Vanninathan, Astrid M. Veronig, Karin Dissauer, Manuela Temmer
Projects: SDO-AIA

Publication Status: Astrophysical Journal, in press
Last Modified: 2018-02-28 13:59
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Forecasting the Maxima of Solar Cycle 24 with Coronal Fe XIV Emission    

Richard Altrock   Submitted: 2012-09-12 12:42

The onset of the ''Rush to the Poles'' of polar crown prominences and their associated coronal emission is a harbinger of solar maximum. Altrock (Solar Phys. 216, 343, 2003) showed that the ''Rush'' was well-observed in the Fe XIV corona at the Sacramento Peak site of the National Solar Observatory prior to the maxima of Cycles 21 to 23. The data show that solar maximum in those cycles occurred when the center line of the Rush reached a critical latitude of 76? ? 2?. Furthermore, in the previous three cycles solar maximum occurred when the number of Fe XIV emission regions per day > 0.19 (averaged over 365 days and both hemispheres) first reached latitudes 20? ? 1.7?. Applying the above conclusions to Cycle 24 is difficult due to the unusual nature of this cycle. Cycle 24 displays an ... [READ MORE]

Authors: Richard C. Altrock
Projects: National Solar Observatory (Sac Peak)

Publication Status: submitted to Solar Physics
Last Modified: 2012-09-13 10:14
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A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. IV. Unusual Magnetic Cloud and Overall Scenario    

Victor Grechnev   Submitted: 2014-09-02 00:06

The geomagnetic superstorm of 20 November 2003 with Dst = -422 nT, one of the most intense in history, is not well understood. The superstorm was caused by a moderate solar eruptive event on 18 November, comprehensively studied in our preceding Papers I-III. The analysis has shown a number of unusual and extremely complex features, which presumably led to the formation of an isolated right-handed magnetic-field configuration. Here we analyze the interplanetary disturbance responsible for the 20 November superstorm, compare some of its properties with the extreme 28-29 October event, and reveal a compact size of the magnetic cloud (MC) and its disconnection from the Sun. Most likely, the MC had a spheromak configuration and expanded in a narrow angle of < 14 degree. A very strong magnetic ... [READ MORE]

Authors: V. V. Grechnev, A. M. Uralov, I. M. Chertok, A. V. Belov, B. P. Filippov, V. A. Slemzin, B. V. Jackson
Projects: ACE,Neutron Monitors,Other

Publication Status: Solar Phys., accepted
Last Modified: 2014-09-03 13:11
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The Effect of Radiative Cooling on Coronal Loop Oscillations    

Markus J. Aschwanden   Submitted: 2008-09-02 14:16

Coronal loops that exhibit kink-mode oscillations have generally been assumed to have a constant density and temperature during the observed time interval. Analyzing their intensities in an EUV waveband, however, clearly shows that their brightness varies in a way that is consistent with a temperature cooling through the EUV passband, which limits their detection time, observed damping time, and number of observable periods. We study kink-mode oscillations of eight loops observed during the so-called ``harmonica event'' on 2001-Apr-15, 21:58-22:27 UT in 171 ang . We find loop densities of n_e=(1.4+/-0.6) x 10^9 cm^-3, loop widths of w=2.0 +/- 2.6 Mm, and e-folding cooling times of t_cool=17 +/- 7 min, when they cool through the peak temperature T=0.95 MK of the 171 A band. We ... [READ MORE]

Authors: Markus J. Aschwanden and Jaume Terradas
Projects: TRACE

Publication Status: ApJ 686, L127-L130
Last Modified: 2008-12-02 09:30
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Quasi-periodic Counter-propagating Fast Magnetosonic Wave Trains from Neighboring Flares: SDO/AIA Observations and 3D MHD Modeling    

Leon Ofman   Submitted: 2018-05-01 22:50

Since their discovery by SDO/AIA in EUV, rapid (phase speeds of ~1000 km/s), quasi-periodic, fast-mode propagating wave trains (QFPs) have been observed accompanying many solar flares. They typically propagate in funnel-like structures associated with the expanding magnetic field topology of the active regions (ARs). The waves provide information on the associated flare pulsations and the magnetic structure through coronal seismology. The reported waves usually originate from a single localized source associated with the flare. Here, we report the first detection of counter-propagating QFPs associated with two neighboring flares on 2013 May 22, apparently connected by large-scale, trans-equatorial coronal loops. We present the first results of 3D MHD model of counter-propagating QFPs an ... [READ MORE]

Authors: Leon Ofman; Wei Liu
Projects: SDO-AIA

Publication Status: ApJ, in press
Last Modified: 2018-05-02 12:06
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Pre-flare coronal dimmings    

Qingmin Zhang   Submitted: 2016-11-27 18:45

Coronal dimmings are regions of decreased extreme-ultravoilet (EUV) and/or X-ray (originally Skylab, then Yohkoh/SXT) intensities, which are often associated with flares and coronal mass ejections (CMEs). The large-scale, impulsive dimmings have substantially been observed and investigated. The pre-flare dimmings prior to the flare impulsive phase, however, have rarely been studied in detail. In this paper, we focus on the pre-flare coronal dimmings. We report our multiwavelength observations of the GOES X1.6 solar flare and the accompanying halo CME produced by the eruption of a sigmoidal magnetic flux rope (MFR) in NOAA active region (AR) 12158 on 2014 September 10. The eruption was observed by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamic ... [READ MORE]

Authors: Q. M. Zhang, Y. N. Su, and H. S. Ji
Projects: SDO-AIA

Publication Status: to be accepted for publication by A&A
Last Modified: 2016-11-30 12:19
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Coronal mass ejections, type II radio bursts, and solar energetic particle events in the SOHO era    

Nat Gopalswamy   Submitted: 2008-02-08 15:32

Using the extensive and uniform data on coronal mass ejections (CMEs), solar energetic particle (SEP) events, and type II radio bursts during the SOHO era, we discuss how the CME properties such as speed, width and solar-source longitude decide whether CMEs are associated with type II radio bursts and SEP events. We discuss why some radio-quiet CMEs are associated with small SEP events while some radio-loud CMEs are not associated with SEP events. We conclude that either some fast and wide CMEs do not drive shocks or they drive weak shocks that do not produce significant levels of particle acceleration. We also infer that the Alfv?n speed in the corona and near-Sun interplanetary medium ranges from <200 km/s to ~1600 km/s. Radio-quiet fast and wide CMEs are also poor SEP producers and ... [READ MORE]

Authors: N. Gopalswamy, S. Yashiro, S. Akiyama, P. Makela, H. Xie, M. Kaiser, R. Howard, and J.-L. Bougeret
Projects: SoHO-EIT,SoHO-LASCO

Publication Status: Annales Geophysicae, Accepted for Publication, February 7, 2008
Last Modified: 2008-02-09 21:49
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Chain Reconnections observed in Sympathetic Eruptions    

Navin Chandra Joshi   Submitted: 2016-02-25 21:22

The nature of various plausible causal links between sympathetic events is still a controversial issue. In this work, we present multi-wavelength observations of sympathetic eruptions, associated flares and coronal mass ejections (CMEs) occurring on 2013 November 17 in two close-by active regions. Two filaments i.e., F1 and F2 are observed in between the active regions. Successive magnetic reconnections, caused by different reasons (flux cancellation, shear and expansion) have been identified during the whole event. The first reconnection occurred during the first eruption via flux cancellation between the sheared arcades overlying filament F2, creating a flux rope and leading to the first double ribbon solar flare. During this phase we observed the eruption of overlaying arcades and ... [READ MORE]

Authors: Navin Chandra Joshi, Brigitte Schmieder, Tetsuya Magara, Yang Guo, Guillaume Aulanier
Projects: GOES Particles,GONG,RHESSI,SDO-AIA,SDO-HMI,SoHO-LASCO,STEREO

Publication Status: Accepted for publication in ApJ
Last Modified: 2016-02-29 10:55
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Title: Monte Carlo Markov Chain DEM reconstruction of isothermal plasmas    

Fabio Reale   Submitted: 2011-12-14 03:36

In this paper, we carry out tests on the Monte Carlo Markov Chain (MCMC) technique with the aim of determining: 1) its ability to retrieve isothermal plasmas from a set of spectral line intensities, with and without random noise; 2) to what extent can it discriminate between an isothermal solution and a narrow multithermal distribution; and 3) how well it can detect multiple isothermal components along the line of sight. We also test the effects of 4) atomic data uncertainties on the results, and 5) the number of ions whose lines are available for the DEM reconstruction. We find that the MCMC technique is unable to retrieve isothermal plasmas to better than Delta log T = 0.05. Also, the DEM curves obtained using lines calculated with an isothermal plasma and with a Gaussian distribution ... [READ MORE]

Authors: E. Landi, F. Reale, P. Testa
Projects: Hinode/EIS,Hinode/XRT,SDO-AIA,SDO-EVE,SoHO-CDS,SoHO-SUMER

Publication Status: accepted for publication in A&A
Last Modified: 2011-12-14 08:53
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A New Tool for CME Arrival Time Prediction Using Machine Learning Algorithms: CAT-PUMA    

Jiajia Liu   Submitted: 2018-03-15 05:48

Coronal Mass Ejections (CMEs) are arguably the most violent eruptions in the Solar System. CMEs can cause severe disturbances in the interplanetary space and even affect human activities in many respects, causing damages to infrastructure and losses of revenue. Fast and accurate prediction of CME arrival time is then vital to minimize the disruption CMEs may cause when interacting with geospace. In this paper, we propose a new approach for partial-/full-halo CME Arrival Time Prediction Using Machine learning Algorithms (CAT-PUMA). Via detailed analysis of the CME features and solar wind parameters, we build a prediction engine taking advantage of 182 previously observed geo-effective partial-/full-halo CMEs and using algorithms of the Support Vector Machine (SVM). We demonstrate that ... [READ MORE]

Authors: Jiajia Liu, Yudong Ye, Chenlong Shen, Yuming Wang, Robert Erd?lyi
Projects: SoHO-LASCO

Publication Status: Published, The Astrophysical Journal, 855:109 (10pp), 2018
Last Modified: 2018-03-16 13:38
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Silicon Abundance from RESIK Solar Flare Observations    

Kenneth Phillips   Submitted: 2012-12-13 05:47

The RESIK instrument on the CORONAS-F spacecraft obtained solar flare and active region X-ray spectra in four channels covering the wavelength range 3.8--6.1~AA in its operational period between 2001 and 2003. Several highly ionized silicon lines were observed within the range of the long-wavelength channel (5.00,--,6.05~AA). The fluxes of the sixiv Ly-$eta$ line (5.217~AA) and the sixiii $1s^2 - 1s3p$ line (5.688~AA) during 21 flares with optimized pulse-height analyzer settings on RESIK have been analyzed to obtain the silicon abundance relative to hydrogen in flare plasmas. As in previous work, the emitting plasma for each spectrum is assumed to be characterized by a single temperature and emission measure given by the ratio of emission in the two channels of GOES. The silicon ... [READ MORE]

Authors: B. Sylwester, K. J. H. Phillips, J. Sylwester, A. Kepa
Projects: CORONAS-F

Publication Status: Solar Physics (to be published)
Last Modified: 2012-12-14 16:10
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Investigating the Dynamics and Density Evolution of Returning Plasma Blobs from the 2011 June 7 Eruption    

Jack Carlyle   Submitted: 2014-01-22 23:53

This work examines infalling matter following an enormous Coronal Mass Ejection (CME) on 2011 June 7. The material formed discrete concentrations, or blobs, in the corona and fell back to the surface, appearing as dark clouds against the bright corona. In this work we examined the density and dynamic evolution of these blobs in order to formally assess the intriguing morphology displayed throughout their descent. The blobs were studied in five wavelengths (94, 131, 171, 193 and 211 Angstrom) using the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA), comparing background emission to attenuated emission as a function of wavelength to calculate column densities across the descent of four separate blobs. We found the material to have a column density of hydrogen of ... [READ MORE]

Authors: Jack Carlyle, David R. Williams, Lidia van Driel-Gesztelyi, Davina Innes, Andrew Hillier, Sarah Matthews
Projects: SDO-AIA

Publication Status: In press, ApJ
Last Modified: 2014-01-23 10:23
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Large-scale Coronal Propagating Fronts in Solar Eruptions as Observed by the Atmospheric Imaging Assembly on Board the Solar Dynamics Observatory - An Ensemble Study    

Nariaki Nitta   Submitted: 2013-08-18 21:49

This paper presents a study of a large sample of global disturbances in the solar corona with characteristic propagating fronts as intensity enhancement, similar to the phenomena that have often been referred to as EIT waves or EUV waves. Now Extreme Ultraviolet (EUV) images obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provide a significantly improved view of these large-scale coronal propagating fronts (LCPFs). Between April 2010 and January 2013, a total of 171 LCPFs have been identified through visual inspection of AIA images in the 193 A channel. Here we focus on the 138 LCPFs that are seen to propagate across the solar disk, first studying how they are associated with flares, coronal mass ejections (CMEs) and type II radio bursts. ... [READ MORE]

Authors: Nitta, N. V., Schrijver, C. J., Title, A. M., Liu, W.
Projects: SDO-AIA

Publication Status: Published, 2013, ApJ, 776, 58
Last Modified: 2014-09-22 21:07
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Witnessing a Large-scale Slipping Magnetic Reconnection along a Dimming Channel during a Solar Flare    

Ju Jing   Submitted: 2017-06-12 15:24

We report the intriguing large-scale dynamic phenomena associated with the M6.5 flare (SOL2015-06-22T18:23) in NOAA active region 12371, observed by RHESSI, Fermi, and the Atmospheric Image Assembly (AIA) and Magnetic Imager (HMI) on the Solar Dynamic Observatory (SDO). The most interesting feature of this event is a third ribbon (R3) arising in the decay phase, propagating along a dimming channel (seen in EUV passbands) towards a neighboring sunspot. The propagation of R3 occurs in the presence of hard X-ray footpoint emission, and is broadly visible at temperatures from 0.6 MK to over 10 MK through the Differential Emission Measure (DEM) analysis. The coronal loops then undergo an apparent slipping motion following the same path of R3, after a ~80 min delay. To understand the underlying ... [READ MORE]

Authors: Ju Jing, Rui Liu, Mark C. M. Cheung, Jeongwoo Lee, Yan Xu, Chang Liu, Chunming Zhu, and Haimin Wang
Projects: Fermi/GBM,RHESSI,SDO-AIA,SDO-HMI

Publication Status: accepted for publication in ApJL
Last Modified: 2017-06-14 10:02
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How did a Major Confined Flare Occur in Super Solar Active Region 12192?    

Chaowei Jiang   Submitted: 2016-06-30 21:31

We study the physical mechanism of a major X-class solar flare that occurred in the super NOAA active region (AR) 12192 using a data-driven numerical magnetohydrodynamic (MHD) modeling complemented with observations. With the evolving magnetic fields observed at the solar surface as bottom boundary input, we drive an MHD system to evolve self-consistently in correspondence with the realistic coronal evolution. During a two-day time interval, the modeled coronal field has been slowly stressed by the photospheric field evolution,which gradually created a large-scale coronal current sheet, i.e., a narrow layer with intense current, in the core of the AR. The current layer was successively enhanced until it became so thin that a tether-cutting reconnection between the sheared magnetic arcades ... [READ MORE]

Authors: Chaowei Jiang, Shi Tsan Wu, Vasyl B Yurchyshyn, Haimin Wang, Xueshang Feng, Qiang Hu
Projects: SDO-AIA,SDO-HMI

Publication Status: accept by ApJ
Last Modified: 2016-07-06 10:36
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Twisting solar coronal jet launched at the boundary of an active region    

Guillaume Aulanier   Submitted: 2013-09-20 02:41

A broad jet was observed in a weak magnetic field area at the edge of active region NOAA 11106 that also produced other nearby recurring and narrow jets. The peculiar shape and magnetic environment of the broad jet raised the question of whether it was created by the same physical processes of previously studied jets with reconnection occurring high in the corona. We carried out a multi-wavelength analysis using the EUV images from the Atmospheric Imaging Assembly (AIA) and magnetic fields from the Helioseismic and Magnetic Imager (HMI) both on-board the SDO satellite, which we coupled to a high-resolution, nonlinear force-free field extrapolation. Local correlation tracking was used to identify the photospheric motions that triggered the jet, and time-slices were extracted along ... [READ MORE]

Authors: Schmieder B., Guo Y., Moreno-Insertis F., Aulanier G., Yelles Chaouche L., Nishizuka N., Harra L.K., Thalmann J.K., Vargas Dominguez S., Liu Y.
Projects: SDO-AIA,SDO-HMI

Publication Status: A&A, in press
Last Modified: 2013-09-22 08:03
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Magnetohydrodynamic Modeling of the Solar Eruption on 2010 April 8    

Bernhard Kliem   Submitted: 2014-07-11 09:00

The structure of the coronal magnetic field prior to eruptive processes and the conditions for the onset of eruption are important issues that can be addressed through studying the magnetohydrodynamic stability and evolution of nonlinear force-free field (NLFFF) models. This paper uses data-constrained NLFFF models of a solar active region that erupted on 2010 April 8 as initial condition in MHD simulations. These models, constructed with the techniques of flux rope insertion and magnetofrictional relaxation, include a stable, an approximately marginally stable, and an unstable configuration. The simulations confirm previous related results of magnetofrictional relaxation runs, in particular that stable flux rope equilibria represent key features of the observed pre-eruption coronal ... [READ MORE]

Authors: B. Kliem, Y. N. Su, A. A. van Ballegooijen, & E. E. DeLuca
Projects: Hinode/XRT,SDO-AIA,SDO-HMI,STEREO

Publication Status: Published in ApJ 779, 129, 2013
Last Modified: 2014-07-11 14:34
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Magnetic Energy Partition between the CME and Flare from AR 11283    

Li Feng   Submitted: 2013-01-16 07:04

On 6 September 2011, an X-class flare and a halo CME as observed from the Earth were erupted from the same active region AR 11283. The magnetic energy partition between them has been investigated. SDO/HMI vector magnetograms were used to obtain the coronal magnetic field with the nonlinear force-free field (NLFFF) extrapolation method. The free magnetic energies before and after the flare were calculated to estimate the released energy available to power the flare and the CME. For the flare energetics, thermal and nonthermal energies were derived using the RHESSI and GOES data. To obtain the radiative output, SDO/EVE data in the 0.1-37 nm waveband were utilized. We have reconstructed the three dimensional (3D) periphery of the CME from the coronagraph images observed by ... [READ MORE]

Authors: L. Feng, T. Wiegelmann, Y. Su, B. Inhester, Y.P. Li, X.D. Sun, W.Q. Gan
Projects: SDO-AIA,SDO-HMI,SDO-EVE,STEREO

Publication Status: ApJ, in press
Last Modified: 2013-01-16 07:37
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X-ray precursors to flares and filament eruptions    

Cristina Chifor   Submitted: 2007-07-03 03:49

Aims: To study preflare X-ray brightenings as diagnostics of the destabilisation of flare-associated erupting filaments/prominences. <BR> Methods: We combine new observations from the Transition Region and Coronal Explorer (TRACE) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), as well as revisit events reported in the literature to date, in order to scrutinise the preflare activity during eight flare-associated filament eruptions. <BR> Results: The preflare activity occurs in the form of discrete, localised X-ray brightenings observed between 2 and 50 minutes before the impulsive phase of the flare and filament acceleration. These transient preflare brightenings are situated on or near (within 10'' of) the polarity inversion line (PIL), ... [READ MORE]

Authors: C. Chifor, D. Tripathi, H. E. Mason, B. R. Dennis
Projects: RHESSI,SoHO-EIT,SoHO-MDI,TRACE

Publication Status: A&A, accepted, in press
Last Modified: 2007-07-03 09:43
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Observations of a Two-stage Solar Eruptive Event (SEE): Evidence for Secondary Heating    

Yang Su   Submitted: 2013-01-17 09:06

We present RHESSI, SDO/AIA, SOHO/LASCO, STEREO, and GOES observations of a partially occulted solar eruptive event that occurred at the southwest limb on 2011 March 8. The GOES X-ray light curve shows two peaks separated by almost 2 hr that we interpret as two stages of a single event associated with the delayed eruption of a coronal mass ejection (CME). A hot flux rope formed during the first stage and continued expanding and rising throughout the event. The speed of the flux rope decreased from ~120 to 14 km s-1 during the decay phase of the first stage and increased again during the second stage to become the CME with a speed of ~516 km s-1. RHESSI and GOES data analyses show that the plasma temperature reached over 20 MK in the first stage, then decreased to ~10 MK and increased to 15 ... [READ MORE]

Authors: Su, Y.; Dennis, B. R.; Holman, G. D.; Wang, T. J.; Chamberlin, P. C.; Savage, S.; Veronig, A.
Projects: GOES X-rays ,SDO-AIA,SDO-EVE,SoHO-LASCO,STEREO

Publication Status: ApJL, 746, L5, 2012
Last Modified: 2013-01-17 14:32
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The Driver of Coronal Mass Ejections in the Low Corona: A Flux Rope    

Xin Cheng   Submitted: 2012-11-28 18:26

Recent Solar Dynamic Observatory observations reveal that coronal mass ejections (CMEs) consist of a multi-temperature structure: a hot flux rope and a cool leading front (LF). The flux rope first appears as a twisted hot channel in the Atmospheric Imaging Assembly 94 A and 131 A passbands. The twisted hot channel initially lies along the polarity inversion line and then rises and develops into the semi-circular flux rope-like structure during the impulsive acceleration phase of CMEs. In the meantime, the rising hot channel compresses the surrounding magnetic field and plasma, which successively stack into the CME LF. In this paper, we study in detail two well-observed CMEs occurred on 2011 March 7 and 2011 March 8, respectively. Each of them is associated with an M-class flare. Through a ... [READ MORE]

Authors: X. Cheng, J. Zhang, D. M. Ding, Y. Liu, W. Poomvises
Projects: SDO-AIA

Publication Status: 18 pages, 12 figures, 1 table, accepted for publication in ApJ
Last Modified: 2012-12-01 23:52
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Solar Center--Limb Variation of the Strengths of Spectral Lines: Classification and Interpretation of Observed Trends    

Yoichi Takeda   Submitted: 2019-05-07 18:54

The equivalent widths (W) of 565 spectral lines in the wavelength range of 4690--6870A were evaluated at 31 consecutive points from the solar disk center (mu=cos(theta)=1) to near the limb (mu=0.25) by applying the synthetic spectrum-fitting technique, in order to clarify the nature of their center--limb variations, especially the observed slope differing from line to line and its interpretation in terms of line properties. We found that the distribution of the gradient beta (= -dlog W/dlog mu) well correlates with that of dlog W/dlog T index, which means that the center-to-limb variation of W is determined mainly by the T-sensitivity of individual lines because the line-forming region shifts towards upper layers of lower T as we go toward the limb. Further, the key to understanding the ... [READ MORE]

Authors: Y. Takeda and S. UeNo
Projects: Domeless Solar Telescope (Hida Observatory)

Publication Status: accepted for publication in Solar Physics
Last Modified: 2019-05-08 09:52
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Correcting for interplanetary scattering in velocity dispersion analysis of solar energetic particles    

Timo Laitinen   Submitted: 2015-04-24 06:41

To understand the origin of Solar Energetic Particles (SEPs), we must study their injection time relative to other solar eruption manifestations. Traditionally the injection time is determined using the Velocity Dispersion Analysis (VDA) where a linear fit of the observed event onset times at 1 AU to the inverse velocities of SEPs is used to derive the injection time and path length of the first-arriving particles. VDA does not, however, take into account that the particles that produce a statistically observable onset at 1 AU have scattered in the interplanetary space. We use Monte Carlo test particle simulations of energetic protons to study the effect of particle scattering on the observable SEP event onset above pre-event background, and consequently on VDA results. We find that the ... [READ MORE]

Authors: T. Laitinen, K. Huttunen-Heikinmaa, E. Valtonen, S. Dalla
Projects: GOES X-rays ,SoHO-LASCO

Publication Status: Accepted for publication in Astrophysical Journal
Last Modified: 2015-04-25 18:48
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Hard X-ray and ultraviolet emission during the 2011 June 7 solar flare    

Andrew Inglis   Submitted: 2013-09-04 08:01

The relationship between X-ray and UV emission during flares, particularly in the context of quasi-periodic pulsations, remains unclear. To address this, we study the impulsive X-ray and UV emission during the eruptive flare of 2011 June 7 utilising X-ray imaging from RHESSI and UV 1700A imaging from SDO/AIA. This event is associated with quasi-periodic pulsations in X-ray and possibly UV emission, as well as substantial parallel and perpendicular motion of the hard X-ray footpoints. The motion of the footpoints parallel to the flare ribbons is unusual; it is shown to reverse direction on at least two occasions. However, there is no associated short-timescale motion of the UV bright regions. Additionally, we find that the locations of the brightest X-ray and UV regions are different, ... [READ MORE]

Authors: A. R. Inglis, H. R. Gilbert
Projects: RHESSI,SDO-AIA,SDO-HMI

Publication Status: ApJ, accepted
Last Modified: 2013-09-04 11:42
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Using Coronal Cells to Infer the Magnetic Field Structure and Chirality of Filament Channels    

Olga Panasenco   Submitted: 2013-06-12 13:52

Coronal cells are visible at temperatures of ~ 1.2 MK in Fe XII coronal images obtained from the Solar Dynamics Observatory (SDO) and Solar Terrestrial Relations Observatory (STEREO) spacecraft. We show that near a filament channel, the plumelike tails of these cells bend horizontally in opposite directions on the two sides of the channel like fibrils in the chromosphere. Because the cells are rooted in magnetic flux concentrations of majority polarity, these observations can be used with photospheric magnetograms to infer the direction of the horizontal field in filament channels and the chirality of the associated magnetic field. This method is similar to the procedure for inferring the direction of the magnetic field and the chirality of the fibril pattern in filament channels from ... [READ MORE]

Authors: N. R. Sheeley, Jr., S. F. Martin, O. Panasenco, H. P. Warren
Projects: SDO-AIA,STEREO

Publication Status: accepted for publication in The Astrophysical Journal
Last Modified: 2013-06-12 13:52
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Quantitative model for the generic 3D shape of ICMEs at 1 AU    

Pascal Demoulin   Submitted: 2016-09-05 05:51

Interplanetary imagers provide 2D projected views of the densest plasma parts of interplanetary coronal mass ejections (ICMEs), while in situ measurements provide magnetic field and plasma parameter measurements along the spacecraft trajectory, that is, along a 1D cut. The data therefore only give a partial view of the 3D structures of ICMEs. By studying a large number of ICMEs, crossed at different distances from their apex, we develop statistical methods to obtain a quantitative generic 3D shape of ICMEs. In a first approach we theoretically obtained the expected statistical distribution of the shock-normal orientation from assuming simple models of 3D shock shapes, including distorted profiles, and compared their compatibility with observed distributions. In a second approach we ... [READ MORE]

Authors: P. Demoulin, M. Janvier, J.J. Masias-Meza and S. Dasso
Projects: ACE

Publication Status: A&A, in press
Last Modified: 2016-09-07 12:12
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The role of radiative losses in the late evolution of pulse-heated coronal loops/strands    

Fabio Reale   Submitted: 2012-05-22 04:25

Radiative losses from optically thin plasma are an important ingredient for modeling plasma confined in the solar corona. Spectral models are continuously updated to include the emission from more spectral lines, with significant effects on radiative losses, especially around 1 MK. We investigate the effect of changing the radiative losses temperature dependence due to upgrading of spectral codes on predictions obtained from modeling plasma confined in the solar corona. The hydrodynamic simulation of a pulse-heated loop strand is revisited comparing results using an old and a recent radiative losses function. We find significant changes in the plasma evolution during the late phases of plasma cooling: when the recent radiative loss curve is used, the plasma cooling rate increases ... [READ MORE]

Authors: F. Reale, E. Landi
Projects: Hinode/EIS,Hinode/XRT,SDO-AIA,TRACE

Publication Status: accepted for publication in A&A
Last Modified: 2012-05-22 08:56
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Spatially resolved observations of a coronal type II radio burst with multiple lanes    

Ivan Zimovets   Submitted: 2015-03-22 03:44

Relative dynamics of the radio sources of the metric type II burst with three emission lanes and coronal mass ejection (CME) occurred in the lower corona (r≲1.5R⊙) during the SOL2011-02-16T14:19 event is studied. The observational data of the Nancay Radioheliograph (NRH) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) are used. These observations are also supplemented by the data sets obtained with the STEREO-A and -B, RHESSI, and GOES spacecraft, as well as with the ground-based solar radio spectrometers. It is found that the sources of the radio burst were located ahead of the expanding CME and had a complex spatial structure. The first and the second lanes were both emitted from the "magnetic funnel" - a bundle of open magnetic field ... [READ MORE]

Authors: Zimovets I.V., Sadykov V.M.
Projects: Nan?ay Radioheliograph,RHESSI,SDO-AIA,STEREO

Publication Status: Adv. Space Res. (published online, in press)
Last Modified: 2015-03-25 08:16
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On the relationship between coronal waves associated with a CME on 5 March 2000    

Durgesh Tripathi   Submitted: 2007-08-14 03:57

Aim: To study the relationship between coronal mass ejection (CME) associated waves. Methods: Analysis of CME eruption observations on 5 Mar. 2000 recorded by the Large Angle Spectrometric Coronagraph (LASCO), the Ultraviolet Coronagraph Spectrometer (UVCS), and the Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO). Results: Images recorded by the LASCO/C2 show a clear deflection and kink in a streamer located eastward of the CME. The kink in the streamer propagated outwards along with the associated CME. No CME material was seen between the bright front of the CME and the streamer. UVCS spectra show large spectral line broadening, Doppler shifts and intensity changes in the ion{O}{vi} ($lambda$1032 & 1037) lines. Moreover, ... [READ MORE]

Authors: D. Tripathi and N.-E.Raouafi
Projects: SoHO-EIT,SoHO-LASCO,SoHO-SUMER

Publication Status: Accepted for publication in Astronomy and Astrophysics
Last Modified: 2007-08-14 07:35
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Quantifying the relationship between Moreton-Ramsey waves and "EIT waves" using observations of 4 homologous wave events    

David Long   Submitted: 2019-07-19 02:34

Freely-propagating global waves in the solar atmosphere are commonly observed using Extreme UltraViolet passbands (EUV or "EIT waves"), and less regularly in H-alpha (Moreton-Ramsey waves). Despite decades of research, joint observations of EUV and Moreton-Ramsey waves remain rare, complicating efforts to quantify the connection between these phenomena. We present observations of four homologous global waves originating from the same active region between 28-30 March 2014 and observed using both EUV and H-alpha data. Each global EUV wave was observed by the Solar Dynamics Observatory, with the associated Moreton-Ramsey waves identified using the Global Oscillations Network Group (GONG) network. All of the global waves exhibit high initial velocity (e.g., 842-1388 km/s in the 193A ... [READ MORE]

Authors: David Long, Jack Jenkins, Gherardo Valori
Projects: GONG,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJ
Last Modified: 2019-07-20 21:30
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EIT and TRACE responses to flare plasma    

Durgesh Tripathi   Submitted: 2006-11-06 09:38

Aims: To understand the contribution of active region and flare plasmas to the 195 A channels of SOHO/EIT (Extreme-ultraviolet Imaging Telescope) and TRACE (Transition Region and Coronal Explorer). Methods: We have analysed an M8 flare simultaneously observed by the Coronal Diagnostic Spectrometer (CDS), EIT, TRACE and RHESSI. We obtained synthetic spectra for the flaring region and an outer region using the differential emission measures (DEM) of emitting plasma based on CDS and RHESSI observations and the CHIANTI atomic database. We then predicted the EIT and TRACE count rates. Results: For the flaring region, both EIT and TRACE images taken through the 195 A filter are dominated by Fe XXIV (formed at about 20 MK). However, in the outer region, the emission was primarily due to ... [READ MORE]

Authors: D. Tripathi, G. Del Zanna, H. E. Mason, C. Chifor
Projects: SoHO-EIT,SoHO-CDS,TRACE

Publication Status: Accepted for publication in A&A letters
Last Modified: 2006-11-06 09:46
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Validation of a Scaling Law for the Coronal Magnetic Field Strengths and Loop Lengths of Solar and Stellar Flares    

Kosuke Namekata   Submitted: 2016-10-31 19:51

Shibata & Yokoyama (1999, 2002) proposed a method of estimating the coronal magnetic field strengths ($B$) and magnetic loop lengths ($L$) of solar and stellar flares, on the basis of magnetohydrodynamic simulations of the magnetic reconnection model. Using the scaling law provided by Shibata & Yokoyama (1999, 2002), $B$ and $L$ are obtained as functions of the emission measure ($EM=n^2L^3$) and temperature ($T$) at the flare peak. Here, $n$ is the coronal electron density of the flares. This scaling law enables the estimation of $B$ and $L$ for unresolved stellar flares from the observable physical quantities $EM$ and $T$, which is helpful for studying stellar surface activities. To apply this scaling law to stellar flares, we discuss its validity for spatially resolved solar flares. ... [READ MORE]

Authors: Kosuke Namekata, Takahito Sakaue, Kyoko Watanabe, Ayumi Asai, Kazunari Shibata
Projects: GOES X-rays,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in PASJ
Last Modified: 2016-11-02 08:41
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A Very Narrow RHESSI X-ray Flare on 25 September 2011    

Brian Dennis   Submitted: 2019-10-30 09:15

The unusually narrow X-ray source imaged with RHESSI during an impulsive spike lasting for $\sim$10~s during the GOES C7.9 flare on 25 September 2011 (SOL2011-09-25T03:32) was only $\sim$2~arcsec wide and $\sim$10~arcsec long. Comparison with HMI magnetograms and AIA images at 1700~\AA~shows that the X-ray emission was primarily from a long ribbon in the region of positive polarity with little if any emission from the negative polarity ribbon. However, a thermal plasma source density of $\sim$10$^{12}~cm^{-3}$ estimated from the RHESSI-derived emission measure and source area showed that this could best be interpreted as a coronal hard X-ray source in which the accelerated electrons with energies less than $\sim$50~keV were stopped by Coulomb collisions in the corona, thus explaining the ... [READ MORE]

Authors: Brian R. Dennis, Anne K. Tolbert
Projects: GOES X-rays,RHESSI,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in the Astrophysical Journal
Last Modified: 2019-10-30 13:06
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Observations and Magnetic Field Modeling of a Solar Polar Crown Prominence    

Yingna Su   Submitted: 2012-08-07 15:58

We present observations and magnetic field modeling of the large polar crown prominence that erupted on 2010 December 6. Combination of SDO/AIA and STEREO_Behind/EUVI allows us to see the fine structures of this prominence both at the limb and on the disk. We focus on the structures and dynamics of this prominence before the eruption. This prominence contains two parts: an active region part containing mainly horizontal threads, and a quiet Sun part containing mainly vertical threads. On the northern side of the prominence channel, both AIA and EUVI observe bright features which appear to be the lower legs of loops that go above then join in the filament. Filament materials are observed to frequently eject horizontally from the active region part to the quiet Sun part. This ejection ... [READ MORE]

Authors: Yingna Su and Adriaan van Ballegooijen
Projects: SDO-AIA

Publication Status: 2012 ApJ, in press
Last Modified: 2012-08-08 12:14
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Multi-wavelength fine structure and mass flows in solar microflares    

Sigrid Berkebile-Stoiser   Submitted: 2009-08-18 07:57

Aims. We study the multi-wavelength characteristics at high spatial resolution, as well as chromospheric evaporation signatures of solar microflares. To this end, we analyze the fine structure and mass flow dynamics in the chromosphere, transition region and corona of three homologous microflares (GOES class <A9/0.7 with/without background), which occurred on July 4, 2006 in AR 10898. Methods. A multi-wavelength analysis using temporally and spatially highly resolved imaging data from the Dutch open telescope (H alpha, Ca II H), the transition region and coronal explorer (17.1 nm), the extreme-ultraviolet imaging telescope (19.5 nm), and the Reuven Ramaty high energy solar spectroscopic imager (>3 keV) was carried out. EUV line spectra provided by the coronal diagnostic ... [READ MORE]

Authors: Berkebile-Stoiser, S. ; G?m?ry, P.; Veronig, A.M.; Ryb?ak, J.; S?tterlin, P.
Projects: Dutch Open Telescope,RHESSI,SoHO-EIT,SoHO-MDI,SoHO-CDS,TRACE

Publication Status: in press
Last Modified: 2009-08-18 08:39
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Elemental abundances and temperatures of quiescent solar active region cores from X-ray observations    

Giulio Del Zanna   Submitted: 2014-05-07 02:25

A brief review of studies of elemental abundances and emission measures in quiescent solar active region cores is presented. Hinode EUV Imaging Spectrometer (EIS) observations of strong iron spectral lines have shown sharply peaked distributions around 3 MK. EIS observations of lines emitted by a range of elements have allowed good estimates of abundances relative to iron. However, X-ray observations are required to measure the plasma emission above 3 MK and the abundances of oxygen and neon. We revisit, using up-to-date atomic data, older X-ray observations obtained by a sounding rocket and by the Solar Maximum Mission (SMM) Flat Crystal Spectrometer (FCS). We find that the Fe/O and Fe/Ne ratios are normally increased by a factor of 3.2, compared to the photospheric values. Similar ... [READ MORE]

Authors: Del Zanna, G. and Mason, H.E.
Projects: Solar Max Misson

Publication Status: printed, DOI: 10.1051/0004-6361/201423471
Last Modified: 2014-05-07 06:01
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Automated recognition of coronal mass ejections (CMEs) in near-real-time data    

Eva Robbrecht   Submitted: 2004-06-24 01:19

This paper presents a new method and first applications of software that we have developed to autonomously detect CMEs in image sequences from LASCO (Large Angle Spectrometric Coronagraph). The crux of the software is the detection of CMEs as bright ridges in [time,height] maps using the Hough transform. The next step employs clustering and morphological closing operations to mark out different CMEs. The output is a list of events, similar to the classic catalogs, with starting time, principle angle, angular width and velocity estimation for each CME. In addition we present a new type of CME overview map that clearly shows all detected CMEs in a [principal angle, time of occurrence] coordinate system. In contrast to catalogs assembled by human operators, these CME detections can be done ... [READ MORE]

Authors: E. Robbrecht, D. Berghmans
Projects: Soho-LASCO

Publication Status: A&A (in press)
Last Modified: 2004-06-24 01:22
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Untwisting and Disintegration of a Solar Filament Associated with Photospheric Flux Cancellation    

Huadong Chen   Submitted: 2018-12-19 02:27

Using the high-resolution observations from New Vacuum Solar Telescope (NVST) jointly with the Solar Dynamics Observatory data, we investigate two successive confined eruptions (Erup1 and Erup2) of a small filament in a decaying active region on 2017 November 10. During the process of Erup1, the overlying magnetic arcade is observed to inflate with the rising filament at beginning and then stop the ongoing of the explosion. In the hot EUV channel, a coronal sigmoidal structure appears during the first eruption and fade away after the second one. The untwisting rotation and disintegration of the filament in Erup2 are clearly revealed by the NVST Hα intensity data, hinting at a pre-existing twisted configuration of the filament. By tracking two rotating features in the filament, the ... [READ MORE]

Authors: Huadong Chen, Ruisheng Zheng, Leping Li, Suli Ma, Yi Bi, and Shuhong Yang
Projects: New Vacuum Solar Telescope (NVST),SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in the ApJ
Last Modified: 2018-12-19 12:30
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Stellar Evidence that the Solar Dynamo may be in Transition    

Travis Metcalfe   Submitted: 2016-06-29 10:54

Precise photometry from the Kepler space telescope allows not only the measurement of rotation in solar-type field stars, but also the determination of reliable masses and ages from asteroseismology. These critical data have recently provided the first opportunity to calibrate rotation-age relations for stars older than the Sun. The evolutionary picture that emerges is surprising: beyond middle-age the efficiency of magnetic braking is dramatically reduced, implying a fundamental change in angular momentum loss beyond a critical Rossby number (Ro~2). We compile published chromospheric activity measurements for the sample of Kepler asteroseismic targets that were used to establish the new rotation-age relations. We use these data along with a sample of well characterized solar analogs from ... [READ MORE]

Authors: Travis S. Metcalfe, Ricky Egeland, Jennifer van Saders
Projects: Mount Wilson Observatory,Other

Publication Status: ApJL (accepted)
Last Modified: 2016-06-29 13:47
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The role of observed MHD oscillations and waves for coronal heating (Invited Review)    

Markus J. Aschwanden   Submitted: 2004-10-01 14:55

In this review we investigate the role of observed coronal wave and oscillation phenomena with respect to the coronal heating problem. A number of wave phenomena have been recently identified with TRACE and SOHO observations, such as standing waves in the fast kink mode and in the slow acoustic mode, as well as propagating acoustic waves, along closed and open magnetic field lines. Most of these wave phenomena have been detected with periods in the order of minutes to half an hour, constrained by the cadence of available imaging instruments. We find that MHD oscillations and waves with acoustic phase speed carry insufficient energy to contribute significantly to coronal heating. However, MHD oscillation and wave phenomena with Alfv'enic phase speed carry an energy flux that is ... [READ MORE]

Authors: Markus J. Aschwanden
Projects: Soho-EIT,TRACE

Publication Status: in Proc. Coronal Heating, SOHO-15 Workshop, held in St.Andrews, UK, ed. ESA, ESTEC Noordwijk, The Netherlands, Special Publicati
Last Modified: 2004-10-01 14:57
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Observation of 2011-02-15 X2.2 flare in Hard X-ray and Microwave    

Natsuha Kuroda   Submitted: 2015-06-04 22:48

Previous studies have shown that the energy release mechanism of some solar flares follow the Standard magnetic-reconnection model, but the detailed properties of high-energy electrons produced in the flare are still not well understood. We conducted a unique, multi-wavelength study that discloses the spatial, temporal and energy distributions of the accelerated electrons in the X2.2 solar flare on 2011, Feb. 15. We studied the source locations of seven distinct temporal peaks observed in hard X-ray (HXR) and microwave (MW) lightcurves using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in 50 to 75 keV channels and Nobeyama Radioheliograph (NoRH) in 34 GHz, respectively. We found that the seven emission peaks did not come from seven spatially distinct sites in HXR and ... [READ MORE]

Authors: Natsuha Kuroda, Haimin Wang, Dale E. Gary
Projects: Nobeyama Radioheliograph,RHESSI,SDO-AIA,SDO-HMI

Publication Status: ApJ (in press)
Last Modified: 2015-06-05 05:59
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Onset of a Large Ejective Solar Eruption from a Typical Coronal-Jet-Base Field Configuration    

Navin Chandra Joshi   Submitted: 2017-07-04 22:04

Utilizing multiwavelength observations and magnetic field data from SDO/AIA, SDO/HMI, GOES and RHESSI, we investigate a large-scale ejective solar eruption of 2014 December 18 from active region NOAA 12241. This event produced a distinctive three-ribbon flare, having two parallel ribbons corresponding to the ribbons of a standard two-ribbon flare, and a larger-scale third quasi-circular ribbon offset from the other two ribbons. There are two components to this eruptive event. First, a flux rope forms above a strong-field polarity-inversion line and erupts and grows as the parallel ribbons turn on, grow, and spread part from that polarity-inversion line; this evolution is consistent with the tether-cutting-reconnection mechanism for eruptions. Second, the eruption of the arcade that has ... [READ MORE]

Authors: Navin Chandra Joshi, Alphonse C. Sterling, Ronald L. Moore, Tetsuya Magara, Young-Jae Moon
Projects: GOES X-rays,RHESSI,SDO-AIA,SDO-HMI,SoHO-LASCO

Publication Status: Accepted for publication in ApJ Journal.
Last Modified: 2017-07-05 12:50
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Explosive events associated with a surge    

Maria Madjarska   Submitted: 2009-06-10 07:54

The solar atmosphere contains a wide variety of small-scale transient features. Here, we explore the inter-relation between some of them such as surges, explosive events and blinkers via simultaneous spectral and imaging data taken with the TRACE imager, the SUMER, and CDS spectrometers on board SoHO, and SVST La Palma. The features were observed in spectral lines with formation temperatures from 10,000 K to 1 MK and with the TRACE Fe ix/x 171 A filter. The Halpha filtergrams were taken in the wings of the H 6365 A line at ?700 mA and ?350 mA. The alignment of all data both in time and solar XY shows that SUMER line profiles, which are attributed to explosive events, are due to a surge phenomenon. The surge?s up- and down-flows which often appear simultaneously correspond to ... [READ MORE]

Authors: M.S. Madjarska, J.G. Doyle & B. de Pontieu
Projects: SoHO-SUMER,TRACE

Publication Status: ApJ Part I, in press
Last Modified: 2009-06-10 09:19
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Impulsive coronal heating from large-scale magnetic rearrangements: from IRIS to SDO/AIA    

Fabio Reale   Submitted: 2019-07-05 02:38

The Interface Region Imaging Spectrograph (IRIS) has observed bright spots at the transition region footpoints associated with heating in the overlying loops, as observed by coronal imagers. Some of these brightenings show significant blueshifts in the Si iv line at 1402.77 A (logT[K] = 4.9). Such blueshifts cannot be reproduced by coronal loop models assuming heating by thermal conduction only, but are consistent with electron beam heating, highlighting for the first time the possible importance of non-thermal electrons in the heating of non-flaring active regions. Here we report on the coronal counterparts of these brightenings observed in the hot channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We show that the IRIS bright spots are the ... [READ MORE]

Authors: Fabio Reale, Paola Testa, Antonino Petralia, David R. Graham
Projects: IRIS,SDO-AIA

Publication Status: Accepted by ApJ
Last Modified: 2019-07-06 18:48
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The width distribution of solar coronal loops and strands - Are we hitting rock bottom ?    

Markus J Aschwanden   Submitted: 2019-06-13 09:55

In this study, we analyze Atmospheric Imaging Assembly (AIA) and Hi-C images in order to investigate absolute limits for the finest loop strands. We develop a model of the occurrence-size distribution function of coronal loop widths, characterized by the lower limit of widths wmin, the peak (or most frequent) width wp, the peak occurrence number np, and a power-law slope a. Our data analysis includes automated tracing of curvilinear features with the OCCULT-2 code, automated sampling of the cross-sectional widths of coronal loops, and fitting of the theoretical size distribution to the observed distribution. With Monte Carlo simulations and variable pixel sizes Δx, we derive a first diagnostic criterion to discriminate whether the loop widths are ... [READ MORE]

Authors: Aschwanden, M.J., Peter, H.
Projects: SDO-AIA

Publication Status: ApJ 840:4 (24pp)
Last Modified: 2019-07-07 03:55
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Microflares and the Statistics of X-ray Flares    

Amir Caspi   Submitted: 2011-10-28 12:21

This review surveys the statistics of solar X-ray flares, emphasising the new views that RHESSI has given us of the weaker events (the microflares). The new data reveal that these microflares strongly resemble more energetic events in most respects; they occur solely within active regions and exhibit high-temperature/nonthermal emissions in approximately the same proportion as major events. We discuss the distributions of flare parameters (e.g., peak flux) and how these parameters correlate, for instance via the Neupert effect. We also highlight the systematic biases involved in intercomparing data representing many decades of event magnitude. The intermittency of the flare/microflare occurrence, both in space and in time, argues that these discrete events do not explain general coronal ... [READ MORE]

Authors: I. G. Hannah, H. S. Hudson, M. Battaglia, S. Christe, J. Kasparova, S. Krucker, M. R. Kundu, A. Veronig
Projects: GONG,Hinode/EIS,Hinode/SOT,Hinode/XRT,Nobeyama Radioheliograph,Owens Valley Solar Array,RHESSI,SDO-AIA,SDO-HMI,SDO-EVE,SoHO-EIT,SoHO-MDI,SoHO-CDS,SoHO-LASCO,SoHO-SUMER,STEREO,TRACE

Publication Status: Published -- Hannah, I. G., et al. 2011, Space Sci. Rev., 159, 263; DOI 10.1007/s11214-010-9705-4
Last Modified: 2011-11-17 14:20
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SDO Observations of Magnetic Reconnection at Coronal Hole Boundaries    

Shuhong Yang   Submitted: 2011-03-18 17:12

With the observations from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory, we investigate the coronal hole boundaries (CHBs) of an equatorial extension of polar coronal hole. At the CHBs, lots of extreme- ultraviolet (EUV) jets, which appear to be the signatures of magnetic reconnection, are observed in the 193Å images, and some jets occur repetitively at the same sites. The evolution of the jets is associated with the emergence and cancelation of magnetic fields. We notice that both the east and the west CHBs shift westward, and the shift velocities are close to the velocities of rigid rotation compared with those of the photospheric differential rotation. This indicates that magnetic reconnection ... [READ MORE]

Authors: Shuhong Yang, Jun Zhang, Ting Li, Yang Liu
Projects: SDO-AIA,SDO-HMI

Publication Status: accepted for publication in ApJL
Last Modified: 2011-03-18 18:20
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Formation and Eruption of an Active Region Sigmoid. II. Magnetohydrodynamic Simulation of a Multistage Eruption    

Chaowei Jiang   Submitted: 2018-10-30 21:05

Solar eruptions, mainly eruptive flares with coronal mass ejections, represent the most powerful drivers of space weather. Due to the low plasma-β nature of the solar corona, solar eruption has its roots in the evolution of the coronal magnetic field. Although various theoretical models of the eruptive magnetic evolution have been proposed, they still oversimplify the realistic process in observation, which shows a much more complex process due to the invisible complex magnetic environment. In this paper, we continue our study of a complex sigmoid eruption in solar active region 11283, which is characterized by a multipolar configuration embedding a null-point topology and a sigmoidal magnetic flux rope. Based on extreme ultraviolet observations, it has been suggested that a ... [READ MORE]

Authors: Chaowei Jiang, Xueshang Feng, and Qiang Hu
Projects: SDO-AIA,SDO-HMI

Publication Status: Published in ApJ
Last Modified: 2018-10-31 12:08
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Homologous large-amplitude Nonlinear fast-mode Magnetosonic Waves Driven by Recurrent Coronal Jets    

Yuandeng Shen   Submitted: 2018-06-07 06:25

The detailed observational analysis of a homologous Extreme-ultraviolet (EUV) wave event is presented to study the driving mechanism and the physical property of the EUV waves, combining high resolution data taken by the Solar Dynamics Observatory and the Solar TErrestrial RElations Observatory. It is observed that four homologous EUV waves originated from the same active region AR11476 within about one hour, and the time separations between consecutive waves were of 8 - 20 minutes. The waves showed narrow arc-shaped wavefronts and propagated in the same direction along a large-scale transequatorial loop system at a speed of 648 - 712 km/s and a deceleration of 0.985 - 1.219 km/s2. The EUV waves were accompanied by weak flares, coronal jets, and radio type III bursts, in which the EUV ... [READ MORE]

Authors: Yuandeng Shen; Yu Liu; Ying D. Liu; Jiangtao Su; Zehao Tang; Yuhu Miao
Projects: SDO-AIA

Publication Status: accepted by apj
Last Modified: 2018-06-07 12:34
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The effect of initial conditions on the electromagnetic radiation generation in type III solar radio bursts    

David Tsiklauri   Submitted: 2013-05-28 01:51

Extensive particle-in-cell simulations of fast electron beams injected in a background magnetised plasma with a decreasing density profile were carried out. These simulations were intended to further shed light on a newly proposed mechanism for the generation of electromagnetic waves in type III solar radio bursts [D. Tsiklauri, Phys. Plasmas, 18, 052903 (2011)]. The numerical simulations were carried out using different density profiles and fast electron distribution functions. It is shown that electromagnetic L and R modes are excited by the transverse current, initially imposed on the system. In the course of the simulations no further interaction of the electron beam with the background plasma could be observed.

Authors: H. Schmitz, D. Tsiklauri
Projects: Nobeyama Radioheliograph,Owens Valley Solar Array

Publication Status: Phys. Plasmas 20, 062903 (2013)
Last Modified: 2016-11-30 11:12
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2D Feature Recognition and 3D Reconstruction in Solar EUV Images    

Markus J. Aschwanden   Submitted: 2005-01-31 18:38

EUV images show the solar corona in a typical temperature range of T~1 MK, which encompasses the most common coronal structures: loops, filaments, and other magnetic structures in active regions, the quiet Sun, and coronal holes. Quantitative analysis increasingly demands automated 2D feature recognition and 3D reconstruction, in order to localize, track, and monitor the evolution of such coronal structures. We discuss numerical tools that ``fingerprint'' curvi-linear 1D features (e.g., loops and filaments). We discuss existing finger-printing algorithms, such as the brightness gradient method, the oriented-connectivity method, stereoscopic methods, time-differencing, and space-time feature recognition. We discuss improved 2D feature recognition and 3D ... [READ MORE]

Authors: Markus J. Aschwanden
Projects: Soho-EIT,Soho-MDI,Soho-CDS,Soho-LASCO,TRACE

Publication Status: Solar Physics, (in press; accepted Feb 17, 2005)
Last Modified: 2005-02-17 12:43
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Large-scale Coronal Propagating Fronts in Solar Eruptions as Observed by the Atmospheric Imaging Assembly on Board the Solar Dynamics Observatory - An Ensemble Study    

Nariaki Nitta   Submitted: 2013-08-18 21:49

This paper presents a study of a large sample of global disturbances in the solar corona with characteristic propagating fronts as intensity enhancement, similar to the phenomena that have often been referred to as EIT waves or EUV waves. Now Extreme Ultraviolet (EUV) images obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provide a significantly improved view of these large-scale coronal propagating fronts (LCPFs). Between April 2010 and January 2013, a total of 171 LCPFs have been identified through visual inspection of AIA images in the 193 A channel. Here we focus on the 138 LCPFs that are seen to propagate across the solar disk, first studying how they are associated with flares, coronal mass ejections (CMEs) and type II radio bursts. ... [READ MORE]

Authors: Nitta, N. V., Schrijver, C. J., Title, A. M., Liu, W.
Projects: SDO-AIA

Publication Status: Published, ApJ, 776, 58 (2013)
Last Modified: 2013-09-30 10:01
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Structure of the transition region and the low corona from TRACE and SDO observations near the limb    

Costas Alissandrakis   Submitted: 2019-07-21 00:57

We examined the structure near the solar limb in TRACE images of the continuum and in the 1600 and 171 A bands as well as in SDO images in the continuum (from HMI) and all AIA bands. The images in different wavelength bands were carefully coaligned by using the position of Mercury for TRACE and Venus for SDO during their transit in front of the solar disk in 1999 and 2012 respectively. Chromospheric absorbing structures in the TRACE 171 A band are best visible 7" above the white light limb, very close to the inner limb, defined as the inflection point of the rising part of the center-to-limb intensity variation. They are correlated with, but are not identical to spicules in emission, seen in the 1600 A band. Similar results were obtained from AIA and SOT images. Tall spicules in 304 A are ... [READ MORE]

Authors: C. E. Alissandrakis, A. Valentino
Projects: SDO-AIA

Publication Status: In press, Solar Physics
Last Modified: 2019-07-21 23:47
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CORONAL LOOP OSCILLATIONS: OVERVIEW OF RECENT RESULTS    

Tongjiang Wang   Submitted: 2003-10-27 02:20

Recent observations by high-resolution space imaging telescopes have revealed a variety of coronal oscillation modes. In addition to observations of transverse kink-mode oscillations and propagating longitudinal waves in coronal loops detected by TRACE and SOHO/EIT, more recently, SOHO/SUMER discovered standing slow magnetoacoustic waves in hot coronal loops through Doppler shift measurements. We present overviews and comparisons of physical properties of different oscillation modes, and discussions of their triggers and dissipation mechanisms. The application of coronal seismology models constrains the coronal magnetic field strength and dissipation efficiency, vital parameters for our understanding of coronal energy transport mechanisms.

Authors: Tongjiang Wang
Projects: Soho-EIT,TRACE

Publication Status: In Proceeding of SOHO 13, Mallorca of Spain, 2003; (invited), ESA SP-547, p.417
Last Modified: 2004-06-27 05:09
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Formation of a rotating jet during the filament eruption on 10-11 April 2013    

Boris Filippov   Submitted: 2015-05-08 00:45

We analyze multi-wavelength and multi-viewpoint observations of a helically twisted plasma jet formed during a confined filament eruption on 10-11 April 2013. Given a rather large scale event with its high spatial and temporal resolution observations, it allows us to clearly understand some new physical details about the formation and triggering mechanism of twisting jet. We identify a pre-existing flux rope associated with a sinistral filament, which was observed several days before the event. The confined eruption of the filament within a null point topology, also known as an Eiffel tower (or inverted-Y) magnetic field configuration results in the formation of a twisted jet after the magnetic reconnection near a null point. The sign of helicity in the jet is found to be the same as ... [READ MORE]

Authors: B. Filippov, A. K. Srivastava, B. N. Dwivedi, S. Masson, G. Aulanier, N. C. Joshi, and W. Uddin
Projects: SDO-AIA,STEREO

Publication Status: Accepted for publication in MNRAS
Last Modified: 2015-05-12 14:02
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Determination of Linear Force-Free Magnetic Field Constant Alpha Using Deep Learning    

Bernard Benson   Submitted: 2017-12-04 17:12

Modeling the coronal magnetic field of the Sun is an important objective in heliophysics. In this study, we illustrate how to use deep learning to estimate the parameter for a magnetic field model. A linear force-free magnetic field configuration is employed to model, as an initial illustration, an active region by using two magnetic dipoles and to determine the associated linear force-free field (LFFF) alpha parameter from a set of pseudocoronal loop images which serve as training and validation sets to existing deep learning algorithms. Our results show very high accuracy of determining the LFFF parameter alpha from pseudocoronal loop images. Keywords?Sun; solar corona; solar activity; magnetic field models; deep learning;

Authors: Bernard Benson, Zhuocheng Jiang, W. David Pan, G. Allen Gary and Qiang Hu
Projects: SDO-AIA

Publication Status: Accepted to CSCI-ISAI 2017, Las Vegas Conference
Last Modified: 2017-12-05 11:51
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Large-scale Coronal Propagating Fronts in Solar Eruptions as Observed by the Atmospheric Imaging Assembly on Board the Solar Dynamics Observatory - An Ensemble Study    

Nariaki Nitta   Submitted: 2013-08-18 21:49

This paper presents a study of a large sample of global disturbances in the solar corona with characteristic propagating fronts as intensity enhancement, similar to the phenomena that have often been referred to as EIT waves or EUV waves. Now Extreme Ultraviolet (EUV) images obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provide a significantly improved view of these large-scale coronal propagating fronts (LCPFs). Between April 2010 and January 2013, a total of 171 LCPFs have been identified through visual inspection of AIA images in the 193 A channel. Here we focus on the 138 LCPFs that are seen to propagate across the solar disk, first studying how they are associated with flares, coronal mass ejections (CMEs) and type II radio bursts. ... [READ MORE]

Authors: Nitta, N. V., Schrijver, C. J., Title, A. M., Liu, W.
Projects: SDO-AIA

Publication Status: Published as ApJ, 776, 58 (2013)
Last Modified: 2015-01-04 10:55
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The LYRA Instrument Onboard PROBA2: Description and In-Flight Performance    

Marie Dominique   Submitted: 2013-02-26 11:26

The Large Yield Radiometer (LYRA) is an XUV-EUV-MUV (soft X-ray to mid-ultraviolet) solar radiometer onboard the European Space Agency PROBA2 mission that was launched in November 2009. LYRA acquires solar irradiance measurements at a high cadence (nominally 20 Hz) in four broad spectral channels, from soft X-ray to MUV, that have been chosen for their relevance to solar physics, space weather and aeronomy. In this article, we briefly review the design of the instrument, give an overview of the data products distributed through the instrument website, and describe the way that data are calibrated. We also briefly present a summary of the main fields of research currently under investigation by the LYRA consortium.

Authors: M. Dominique, J.-F. Hochedez, W. Schmutz, I.E. Dammasch, A.I. Shapiro, M. Kretzschmar, A.N. Zhukov, D. Gillotay, Y. Stockman, A. BenMoussa
Projects: PROBA2/LYRA

Publication Status: Solar Physics (published)
Last Modified: 2013-02-26 15:39
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Vector Magnetic Field Measurements along a Cooled Stereo-imaged Coronal Loop    

Tom Schad   Submitted: 2017-01-18 16:56

The variation of the vector magnetic field along structures in the solar corona remains unmeasured. Using a unique combination of spectropolarimetry and stereoscopy, we infer and compare the vector magnetic field structure and three-dimensional morphology of an individuated coronal loop structure undergoing a thermal instability. We analyze spectropolarimetric data of the He i λ10830 triplet (1s2s{}3{S}1-1s2p{}3{P}{2,1,0}) obtained at the Dunn Solar Telescope with the Facility Infrared Spectropolarimeter on 2011 September 19. Cool coronal loops are identified by their prominent drainage signatures in the He i data (redshifts up to 185 km s-1). Extinction of EUV background radiation along these loops is observed by both the Atmospheric Imaging Assembly on board the Solar Dynamics ... [READ MORE]

Authors: T.A. Schad, M.J. Penn, H. Lin, P.G. Judge
Projects: National Solar Observatory (Sac Peak)

Publication Status: The Astrophysical Journal, Volume 833, Issue 1, article id. 5, 16 pp. (2016)
Last Modified: 2017-01-19 13:31
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The Eruption from a Sigmoidal Solar Active Region on 2005 May 13    

Chang Liu   Submitted: 2007-07-15 12:57

This paper presents a multiwavelength study of the M8.0 flare and its associated fast halo CME that originated from a bipolar active region NOAA 10759 on 2005 May 13. The source active region has a conspicuous sigmoid structure at TRACE 171 A channel as well as in the SXI soft X-ray images, and we mainly concern ourselves with the detailed process of the sigmoid eruption as evidenced by the multiwavelength data ranging from Halpha, WL, EUV/UV, radio, and hard X-rays (HXRs). The most important finding is that the flare brightening starts in the core of the active region earlier than that of the rising motion of the flux rope. This timing clearly addresses one of the main issues in the magnetic eruption onset of sigmoid, namely, whether the eruption is initiated by an internal ... [READ MORE]

Authors: Chang Liu, Jeongwoo Lee, Vasyl Yurchyshyn, Na Deng, Kyung-Suk Cho, Marian Karlicky, and Haimin Wang
Projects: RHESSI,SoHO-EIT,SoHO-LASCO,TRACE

Publication Status: The Astrophysical Journal, accepted July, 2007
Last Modified: 2007-07-15 15:48
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New Vacuum Solar Telescope observations of a flux rope tracked by a filament activation    

Shuhong Yang   Submitted: 2014-03-04 20:07

One main goal of the New Vacuum Solar Telescope (NVST) which is located at the \emph{Fuxian Solar Observatory} is to image the Sun at high resolution. Based on the high spatial and temporal resolution NVST H_alpha data and combined with the simultaneous observations from the \emph{Solar Dynamics Observatory} for the first time, we investigate a flux rope tracked by a filament activation. The filament material is initially located at one end of the flux rope and fills in a section of the rope, and then the filament is activated due to magnetic field cancellation. The activated filament rises and flows along helical threads, tracking out the twisted flux rope structure. The length of the flux rope is about 75 Mm, the average width of its individual threads is 1.11 Mm, and the estimated ... [READ MORE]

Authors: Shuhong Yang, Jun Zhang, Zhong Liu, Yongyuan Xiang
Projects: Other,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2014-03-05 12:24
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Investigating the Kinematics of Coronal Mass Ejections with the Automated CORIMP Catalog    

Jason P. Byrne   Submitted: 2015-06-15 02:16

Studying coronal mass ejections (CMEs) in coronagraph data can be challenging due to their diffuse structure and transient nature, compounded by the variations in their dynamics, morphology, and frequency of occurrence. The large amounts of data available from missions like the Solar and Heliospheric Observatory (SOHO) make manual cataloging of CMEs tedious and prone to human error, and so a robust method of detection and analysis is required and often preferred. A new coronal image processing catalog called CORIMP has been developed in an effort to achieve this, through the implementation of a dynamic background separation technique and multiscale edge detection. These algorithms together isolate and characterise CME structure in the field-of-view of the Large Angle Spectrometric ... [READ MORE]

Authors: Jason P. Byrne
Projects: SoHO-LASCO

Publication Status: Journal of Space Weather & Space Climate (in press)
Last Modified: 2015-06-15 10:45
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Numerical simulations of solar macrospicules    

Dr. A.K. Srivastava   Submitted: 2011-08-29 23:59

Context. We consider a localized pulse in the component of velocity, parallel to the ambient magnetic field lines, that is initially launched in the solar chromosphere. Aims. We aim to generalize the recent numerical model of spicule formation (Murawski & Zaqarashvili 2010) by implementing a VAL-C model of solar temperature. Methods. With the use of the code FLASH we solve two-dimensional ideal magnetohydrodynamic equations numerically to simulate the solar macrospicules. Results. Our numerical results reveal that the pulse located below the transition region triggers plasma perturbations, which exhibit many features of macrospicules. We also present an observational (SDO/AIA 304 A) case study of the macrospicule that approximately mimics the numerical simulations. Conclusions. In ... [READ MORE]

Authors: Murawski, K.; Srivastava, Abhishek K.; Zaqarashvili, T. V.
Projects: SDO-AIA

Publication Status: A&A
Last Modified: 2011-08-30 10:49
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Observations of multiple blobs in homologous solar coronal jets in closed loops    

Qingmin Zhang   Submitted: 2016-01-18 20:58

Coronal bright points (CBPs) and jets are ubiquitous small-scale brightenings that are often associated with each other. In this paper, we report our multiwavelength observations of two groups of homologous jets. The first group was observed by the \textit{Extreme-Ultraviolet Imager} (EUVI) aboard the behind \textit{Solar TErrestrial RElations Observatory} (STEREO) spacecraft in 171 {\AA} and 304 {\AA} on 2014 September 10, from a location where data from the \textit{Solar Dynamic Observatory} (SDO) could not observe. The jets (J1$-$J6) recurred for six times with intervals of 5$-$15 minutes. They originated from the same primary CBP (BP1) and propagated in the northeast direction along large-scale, closed coronal loops. Two of the jets (J3 and J6) produced sympathetic CBPs ... [READ MORE]

Authors: Q. M. Zhang, H. S. Ji, and Y. N. Su
Projects: SDO-AIA

Publication Status: accepted for publication in Solar Physics
Last Modified: 2016-01-20 12:25
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Fine-scale Structures of Flux Ropes Tracked by Erupting Material    

Ting Li   Submitted: 2013-05-12 23:12

We present the Solar Dynamics Observatory observations of two flux ropes respectively tracked out by material from a surge and a failed filament eruption on 2012 July 29 and August 04. For the first event, the interaction between the erupting surge and a loop-shaped filament in the east seems to ``peel off'' the filament and add bright mass into the flux rope body. The second event is associated with a C-class flare that occurs several minutes before the filament activation. The two flux ropes are respectively composed of 85$pm$12 and 102$pm$15 fine-scale structures, with an average width of about 1$arcsec$.6. Our observations show that two extreme ends of the flux rope are rooted in the opposite polarity fields and each end is composed of multiple footpoints (FPs) of the fine-scale ... [READ MORE]

Authors: Ting Li & Jun Zhang
Projects: SDO-AIA

Publication Status: 14 pages,5 figures, ApJL (accepted)
Last Modified: 2013-05-13 10:03
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Round-Trip Slipping Magnetic Reconnection Observed in a Fan-Spine Jet    

Yuandeng Shen   Submitted: 2019-10-16 20:57

A solar jet on 2014 July 31, which was accompanied by a GOES C1.3 flare and a mini-filament eruption at the jet base, was studied by using observations taken by the New Vacuum Solar Telescope and the Solar Dynamic Observatory. Magnetic field extrapolation revealed that the jet was confined in a fan-spine magnetic system that hosts a null point at the height of about 9 Mm from the solar surface. An inner flare ribbon surrounded by an outer circular ribbon and a remote ribbon were observed to be associated with the eruption, in which the inner and remote ribbons respectively located at the footprints of the inner and outer spines, while the circular one manifested the footprint of the fan structure. It is interesting that the circular ribbon's west part showed an interesting round-trip ... [READ MORE]

Authors: Yuandeng Shen; Zhining Qu; Chengrui Zhou; Yadan Duan; Zehao Tang; Ding Yuan
Projects: SDO-AIA

Publication Status: accepted by ApJL
Last Modified: 2019-10-18 09:50
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Multi-wavelength study of coronal waves associated with the CME-flare event of 03 November 2003    

Astrid Veronig   Submitted: 2005-09-30 03:26

The large flare/CME event that occurred close to the west solar limb on 3 November 2003, launched a large-amplitude large-scale coronal wave which was imaged in H-alpha and Fe XII 195 A spectral lines, as well as in the soft X-ray and radio wavelength range. The wave excited also a complex decimeter-to-hectometer type II radio burst, revealing the formation of coronal shock(s). The back-extrapolation of the motion of coronal wave signatures and the type II burst sources distinctly marks the impulsive phase of the flare (the hard X-ray peak, drifting microwave burst, and the highest type III burst activity), favoring the flare-ignited wave scenario. On the other hand, the comparison of the kinematics of the CME expansion with the propagation of the optical wave signatures and type II burst ... [READ MORE]

Authors: B. Vrsnak, A. Warmuth, M. Temmer, A. Veronig, J. Magdalenic, A. Hillaris, M. Karlicky
Projects: RHESSI,Soho-EIT,Soho-MDI,Soho-LASCO

Publication Status: A&A (in press)
Last Modified: 2005-09-30 03:26
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Deducing Electron Properties From Hard X-Ray Observations    

Amir Caspi   Submitted: 2011-10-28 12:22

X-radiation from energetic electrons is the prime diagnostic of flare-accelerated electrons. The observed X-ray flux (and polarization state) is fundamentally a convolution of the cross-section for the hard X-ray emission process(es) in question with the electron distribution function, which is in turn a function of energy, direction, spatial location and time. To address the problems of particle propagation and acceleration one needs to infer as much information as possible on this electron distribution function, through a deconvolution of this fundamental relationship. This review presents recent progress toward this goal using spectroscopic, imaging and polarization measurements, primarily from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Previous conclusions ... [READ MORE]

Authors: E.P. Kontar, J.C. Brown, A.G. Emslie, W. Hajdas, G.D. Holman, G. J. Hurford, J. Kasparova, P. C. V. Mallik, A. M. Massone, M. L. McConnell, M. Piana, M. Prato, E. J. Schmahl, E. Suarez-Garcia
Projects: GONG,Hinode/EIS,Hinode/SOT,Hinode/XRT,Nobeyama Radioheliograph,Owens Valley Solar Array,RHESSI,SDO-AIA,SDO-HMI,SDO-EVE,SoHO-EIT,SoHO-MDI,SoHO-CDS,SoHO-LASCO,SoHO-SUMER,STEREO,TRACE

Publication Status: Published -- Kontar, E. P., et al. 2011, Space Sci. Rev., 159, 301; DOI 10.1007/s11214-011-9804-x
Last Modified: 2011-11-17 14:20
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Motion magnification in coronal seismology    

Sergey Anfinogentov   Submitted: 2016-11-08 03:15

We introduce a new method for the investigation of low-amplitude transverse oscillations of solar plasma non-uniformities, such as coronal loops, individual strands in coronal arcades, jets, prominence fibrils, polar plumes, and other contrast features, observed with imaging instruments. The method is based on the two-dimensional dual tree complex wavelet transform (DTCWT). It allows us to magnify transverse, in the plane-of-the-sky, quasi-periodic motions of contrast features in image sequences. The tests performed on the artificial data cubes imitating exponentially decaying, multi-periodic and frequency-modulated kink oscillations of coronal loops showed the effectiveness, reliability and robustness of this technique. The algorithm was found to give linear scaling of the magnified ... [READ MORE]

Authors: Sergey Anfinogentov and Valery M. Nakariakov
Projects: SDO-AIA

Publication Status: Solar Physics (accepted)
Last Modified: 2016-11-09 08:47
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Direct Imaging by SDO/AIA of Quasi-periodic Propagating Fast Mode Magnetosonic Waves Propagating of ~2000 km/s in the Low Solar Corona    

Wei Liu   Submitted: 2011-06-15 12:22

Quasi-periodic, propagating fast mode magnetosonic waves in the corona were difficult to observe in the past due to relatively low instrument cadences. We report here evidence of such waves directly imaged in EUV by the new SDO AIA instrument. In the 2010 August 1 C3.2 flare/CME event, we find arc-shaped wave trains of 1-5% intensity variations (lifetime ~200 s) that emanate near the flare kernel and propagate outward up to ~400 Mm along a funnel of coronal loops. Sinusoidal fits to a typical wave train indicate a phase velocity of 2200 +/- 130 km/s. Similar waves propagating in opposite directions are observed in closed loops between two flare ribbons. In the k-$omega$ diagram of the Fourier wave power, we find a bright ridge that represents the dispersion relation and can be well ... [READ MORE]

Authors: Wei Liu, Alan M. Title, Junwei Zhao, Leon Ofman, Carolus J. Schrijver, Markus J. Aschwanden, Bart De Pontieu, and Theodore D. Tarbell
Projects: SDO-AIA

Publication Status: Accepted by ApJ Letters (AAS/SPD Press Release, Las Cruces, June 15, http://www.lmsal.com/press/apjl2011_magnetosonic)
Last Modified: 2011-06-18 06:54
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Comparison of Five Numerical Codes for Automated Tracing of Coronal Loops    

Markus J. Aschwanden   Submitted: 2007-05-21 13:11

The 3D modeling of coronal loops and filaments requires algorithms that automatically trace curvi-linear features in solar EUV or soft X-ray images. We compare 5 existing algorithms that have been developed and customized to trace curvi-linear features in solar images: (1) oriented-connectivity method (OCM), which is an extension of the Strous pixel labeling algorithm (developed by Lee, Newman, and Gary); (2) dynamic aperture-based loop segmentation method (developed by Lee, Newman, and Gary); (3) unbiased detection of curvi-linear structures (developed by Steger, Raghupathy, and Smith); (4) oriented-direction method (developed by Aschwanden); and (5) ridge detection by automated scaling method (developed by Inhester). We test the 5 existing ... [READ MORE]

Authors: Markus Aschwanden, Jong Kwan Lee, G. Allen Gary, Mike Smith, & Bernd Inhester
Projects: TRACE

Publication Status: submitted to Solar Physics for Topical Issue on Challenges in Solar Image Analysis and Visualization, presented at 3rd Solar Image Processing Workshop in Dublin, Ireland, 6-8 Sept 2006
Last Modified: 2007-05-22 08:55
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The GLE on Oct. 28, 2003 - radio diagnostics of relativistic electron and proton injection    

Henry Aurass   Submitted: 2006-08-31 03:00

Timing discrepancies between signatures of accelerated particles at the sun and the arrival times of the particles at near-earth detectors are a matter of fundamental interest for space-weather applications. The solar injection times of various components of energetic particles were derived by Klassen et al. (2005) for the October 28, 2003, X-class / gamma-ray flare in NOAA AR10486. This flare occured in connection with a fast halo coronal mass ejection and a neutron monitor-observed ground level event (GLE). We used radio (Astrophysikalisches Institut Potsdam, WIND, Nancay Multifrequency Radio Heliograph), Halpha (Observatorium Kanzelhoehe), RHESSI, SOHO (EIT, LASCO, MDI), and TRACE data to study the associated chromospheric and low coronal phenomena. We identify three source sites of ... [READ MORE]

Authors: H. Aurass, G. Mann, G. Rausche, and A. Warmuth
Projects: RHESSI,SoHO-EIT,SoHO-MDI,TRACE

Publication Status: A&A 2006 in press
Last Modified: 2006-08-31 10:17
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Comparison between Hinode/SOT and SDO/HMI, AIA Data for the Study of the Solar Flare Trigger Process    

Yumi Bamba   Submitted: 2014-07-07 11:06

Understanding the mechanism that produces solar flares is important not only from the scientific point of view but also for improving space weather predictability. There are numerous observational and computational studies, which attempted to reveal the onset mechanism of solar flares. However, the underlying mechanism of flare onset remains elusive. To elucidate the flare trigger mechanism, we have analyzed several flare events which were observed by Hinode/Solar Optical Telescope (SOT), in our previous study. Because of the limitation of SOT field of view, however, only four events in the Hinode data sets have been utilizable. Therefore, increasing the number of events is required for evaluating the flare trigger models. We investigated the applicability of data obtained by the ... [READ MORE]

Authors: Yumi Bamba, Kanya Kusano, Shinsuke Imada, Yusuke Iida
Projects: Hinode/SOT,SDO-AIA,SDO-HMI

Publication Status: Accepted to PASJ, Hinode special issue
Last Modified: 2014-07-09 13:41
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On the Performance of Multi-Instrument Solar Flare Observations During Solar Cycle 24    

Ryan Milligan   Submitted: 2017-03-14 04:08

The current fleet of space-based solar observatories offers us a wealth of opportunities to study solar flares over a range of wavelengths. Significant advances in our understanding of flare physics often come from coordinated observations between multiple instruments. Consequently, considerable efforts have been, and continue to be made to coordinate observations among instruments (e.g. through the Max Millennium Program of Solar Flare Research). However, there has been no study to date that quantifies how many flares have been observed by combinations of various instruments. Here we describe a technique that retrospectively searches archival databases for flares jointly observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), Solar Dynamics Observatory (SDO)/EUV ... [READ MORE]

Authors: Ryan Milligan, Jack Ireland
Projects: GOES/EUVS,GOES X-rays,Hinode/EIS,Hinode/SOT,Hinode/XRT,IRIS,PROBA2/SWAP,RHESSI,SDO-EVE

Publication Status: 26 pages, 7 figures, 3 tables. Accepted in Solar Physics
Last Modified: 2018-01-09 11:31
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Modelling Quasi-Periodic Pulsations in Solar and Stellar Flares    

James McLaughlin   Submitted: 2018-02-13 04:15

Solar flare emission is detected in all EM bands and variations in flux density of solar energetic particles. Often the EM radiation generated in solar and stellar flares shows a pronounced oscillatory pattern, with characteristic periods ranging from a fraction of a second to several minutes. These oscillations are referred to as quasi-periodic pulsations (QPPs), to emphasise that they often contain apparent amplitude and period modulation. We review the current understanding of quasi-periodic pulsations in solar and stellar flares. In particular, we focus on the possible physical mechanisms, with an emphasis on the underlying physics that generates the resultant range of periodicities. These physical mechanisms include MHD oscillations, self-oscillatory mechanisms, oscillatory ... [READ MORE]

Authors: McLaughlin, J.A., Nakariakov, V.M., Dominique, M., Jel?nek, P., Takasao, S.
Projects: Fermi/GBM,GOES X-rays,Nobeyama Radioheliograph,Other,PROBA2/LYRA,RHESSI

Publication Status: [published] 2018, Space Science Reviews, 214, 45
Last Modified: 2018-02-14 11:41
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Kinematics of ICMEs/Shocks: Blast Wave Reconstruction Using Type-II Emissions   &