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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 physics, we investigate the magnetic configuration and the thermal structure of the flaring region. Our results are in favor of a slipping-type reconnection followed by the thermodynamic evolution of coronal loops. In comparison with those previously reported slipping reconnection events, this one proceeds across a particularly long distance (~60 Mm) over a long period of time (~50 min), and shows two clearly distinguished phases: the propagation of the footpoint brightening driven by nonthermal particle injection and the apparent slippage of loops governed by plasma heating and subsequent cooling.

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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Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6 m New Solar Telescope  

Ju Jing   Submitted: 2016-04-20 08:41

Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6 m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing plasma) streaming down along the post-flare loops, and the chromosphere's response to the impact of coronal rain, showing fine-scale brightenings at the footpoints of the falling plasma. Taking advantage of the resolving power of the NST, we measure the cross sectional widths of flare ribbons, post-flare loops and footpoint brighenings, which generally lie in the range of 80-200 km, well below the resolution of most current instruments used for flare studies. Confining the scale of such fine structure provides an essential piece of information in modeling the energy transport mechanism of flares, which is an important issue in solar and plasma physics.

Authors: Ju Jing, Yan Xu, Wenda Cao, Chang Liu, Dale Gary & Haimin Wang
Projects: BBSO/NST

Publication Status: published in Scientific Reports
Last Modified: 2016-04-20 13:23
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Comparison between the eruptive X2.2 flare on 2011 February 15 and confined X3.1 flare on 2014 October 24  

Ju Jing   Submitted: 2015-08-17 08:16

We compare two contrasting X-class flares in terms of magnetic free energy, relative magnetic helicity and decay index of the active regions (ARs) in which they occurred. The events in question are the eruptive X2.2 flare from AR 11158 accompanied by a halo coronal mass ejection (CME) and the confined X3.1 flare from AR 12192 with no associated CME. These two flares exhibit similar behavior of free magnetic energy and helicity buildup for a few days preceding them. A major difference between the two flares is found to lie in the time-dependent change of magnetic helicity of the ARs that hosted them. AR 11158 shows a significant decrease in magnetic helicity starting ~4 hours prior to the flare, but no apparent decrease in helicity is observed in AR 12192. By examining the magnetic helicity injection rates in terms of sign, we confirmed that the drastic decrease in magnetic helicity before the eruptive X2.2 flare was not caused by the injection of reversed helicity through the photosphere but rather the CME-related change in the coronal magnetic field. Another major difference we find is that AR 11158 had a significantly larger decay index and therefore weaker overlying field than AR 12192. These results suggest that the coronal magnetic helicity and the decay index of the overlying field can provide a clue about the occurrence of CMEs.

Authors: Ju Jing, Yan Xu, Jeongwoo Lee, Nariaki V. Nitta, Chang Liu, Sung-Hong Park, Thomas Wiegelmann, Haimin Wang
Projects: SDO-HMI

Publication Status: published
Last Modified: 2015-08-17 15:11
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Evolution of Magnetic Flux Rope and Its Overlying Arcade Based on Nonlinear Force-free Field Extrapolations  

Ju Jing   Submitted: 2014-03-11 09:17

Dynamic phenomena indicative of slipping reconnection and magnetic implosion were found in a time series of nonlinear force-free field (NLFFF) extrapolations for the active region 11515, which underwent significant changes in the photospheric fields and produced five C-class flares and one M-class flare over five hours on 2012 July 2. NLFFF extrapolation was performed for the uninterrupted 5 hour period from the 12 minute cadence vector magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory. According to the time-dependent NLFFF model, there was an elongated, highly sheared magnetic flux rope structure that aligns well with an Hα filament. This long filament splits sideways into two shorter segments, which further separate from each other over time at a speed of 1-4 km s-1, much faster than that of the footpoint motion of the magnetic field. During the separation, the magnetic arcade arching over the initial flux rope significantly decreases in height from ~4.5 Mm to less than 0.5 Mm. We discuss the reality of this modeled magnetic restructuring by relating it to the observations of the magnetic cancellation, flares, a filament eruption, a penumbra formation, and magnetic flows around the magnetic polarity inversion line.

Authors: Ju Jing, Chang Liu, Jeongwoo Lee, Shuo Wang, Thomas Wiegelmann, Yan Xu, and Haimin Wang
Projects: SDO-HMI

Publication Status: ApJ, 784, L13
Last Modified: 2014-03-12 09:55
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Nonlinear Force-free Modeling of Magnetic Fields in a Solar Filament  

Ju Jing   Submitted: 2010-07-23 09:45

We present a striking filament pattern in the nonlinear force-free (NLFF) chromospheric magnetic field of the active region NOAA 10956. The NLFF chromospheric field is extrapolated from the Hinode high-resolution photospheric vector magnetogram using the weighted optimization method. The modeled structure is characterized by a highly sheared field with strong horizontal magnetic components and has a virtually identical shape and location as the filament seen in Hα. The modeled field strength agrees with the recent He I 10830 Å observations by Kuckein et al.. The unequivocal resemblance between the NLFF extrapolation and the Hα observation not only demonstrates the ability of the NLFF field to reproduce chromospheric features, but also provides a valuable diagnostic tool for the filament magnetic fields.

Authors: Ju Jing, Yuan Yuan, Thomas Wiegelmann, Yan Xu, Rui Liu and Haimin Wang
Projects: Hinode/SOT

Publication Status: The Astrophysical Journal Letters, 719, 56
Last Modified: 2010-07-27 02:46
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Free Magnetic Energy and Flare Productivity of Active Regions  

Ju Jing   Submitted: 2010-03-02 14:19

In this study, the photospheric vector magnetograms, obtained with the Spectro-Polarimeter of the Solar Optical Telescope on board Hinode, are used as the boundary conditions to extrapolate the three-dimensional non-linear force-free (NLFF) coronal magnetic fields. The observed non-force-free photospheric magnetic fields are preprocessed towards the nearly force-free chromospheric magnetic fields. The performance of the preprocessing procedure is evaluated by comparing with chromospheric magnetic fields obtained by the Vector SpectroMagnetograph instrument located on the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Tower. Then the weighted optimization method is applied to the preprocessed boundary data to extrapolate the NLFF fields with which we are able to estimate the free magnetic energy stored in the active regions. The magnitude scaling correlation between the free magnetic energy and the soft X-ray flare index of active regions is then studied. The latter quantifies the impending flare production of active regions over the subsequent 1-, 2- and 3-day time windows. Based on 75 samples, we find a positive correlation between the free energy and the flare index. We also study the temporal variation of free magnetic energy for three active regions, of which two are flare-active and one is flare-quiet during the observation over a period of several days. While the magnitude of free magnetic energy unambiguously differentiates between the flare-active and the flare-quiet regions, the temporal variation of free magnetic energy does not exhibit a clear and consistent pre-flare pattern. This may indicate that the trigger mechanism of flares is as important as the energy storage in active regions.

Authors: Ju Jing, Changyi Tan, Yuan Yuan, Benjamin Wang, Thomas Wiegelmann, Yan Xu, and Haimin Wang
Projects: None

Publication Status: Accepted for Publication in The Astrophysical Journal.
Last Modified: 2010-04-19 09:53
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Temporal Evolution of Free Magnetic Energy Associated with Four X-class Flares  

Ju Jing   Submitted: 2009-02-23 07:06

We study the temporal variation of free magnetic energy Efree around the time of four X-class flares. The high-cadence photospheric vector magnetograms obtained by the digital vector magnegograph (DVMG) system at the Big Bear Solar Observatory (BBSO) are used as the boundary conditions to reconstruct the three-dimensional (3D) non-linear force-free (NLFF) coronal field. In order to remove the effect of the net Lorentz force and torque acting in the photosphere, the vector magnetograms are preprocessed using the method devised by Wiegelmann et al. (2006). Then a well-tested multigrid-like optimization code by Wiegelmann (2004) is applied to the preprocessed boundary data to extrapolate the NLFF coronal field with which we are able to estimate the free energy Efree. In all the four events, we find a significant drop of Efree starting sim15 min before the peak time of the associated non-thermal flare emission, although long term trend varies from event to event. We discuss the physical implication of the result, i.e., the magnetic relaxation is already going on in the corona well before the flare reconnection.

Authors: Ju Jing, P. F. Chen, Thomas Wiegelmann, Yan Xu, Sung-Hong Park, Haimin Wang
Projects:

Publication Status: accepted by Ap.J.
Last Modified: 2010-07-12 08:48
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Abstracts by Author
Witnessing a Large-scale Slipping Magnetic Reconnection along a Dimming Channel during a Solar Flare
Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6 m New Solar Telescope
Comparison between the eruptive X2.2 flare on 2011 February 15 and confined X3.1 flare on 2014 October 24
Evolution of Magnetic Flux Rope and Its Overlying Arcade Based on Nonlinear Force-free Field Extrapolations
Nonlinear Force-free Modeling of Magnetic Fields in a Solar Filament
Free Magnetic Energy and Flare Productivity of Active Regions
Temporal Evolution of Free Magnetic Energy Associated with Four X-class Flares

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