Decoding the Pre-Eruptive Magnetic Field Configurations of Coronal Mass Ejections |
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Spiros Patsourakos Submitted: 2021-02-19 05:07
A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emergence, flux cancellation, helicity condensation). Whether the CME culprit is an SMA or an MFR, however, has been strongly debated for thirty years. We formed an International Space Science Institute (ISSI) team to address and resolve this issue and report the outcome here. We review the status of the field across modeling and observations, identify the open and closed issues, compile lists of SMA and MFR observables to be tested against observations and outline research activities to close the gaps in our current understanding. We propose that the combination of multi-viewpoint multi-thermal coronal observations and multi-height vector magnetic field measurements is the optimal approach for resolving the issue conclusively. We demonstrate the approach using MHD simulations and synthetic coronal images.
Authors: Patsourakos, S., Vourlidas, A., Török, T., Kliem, B., Antiochos, S. K., Archontis, V., Aulanier, G., Cheng, X., Chintzoglou, G., Georgoulis, M. K., Green, L. M., Leake, J. E., Moore, R., Nindos, A., Syntelis, P., Yardley, S. L., Yurchyshyn, V., Zhang, J.
Projects: None
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Publication Status: Space Science Reviews, 2020, Volume 216, Issue 8, article id.131
Last Modified: 2021-02-20 22:48
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Observations of solar chromospheric oscillations at 3 mm with ALMA |
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Spiros Patsourakos Submitted: 2019-12-17 10:14
We studied chromospheric oscillations using Atacama Large millimeter and sub-millimeter Array (ALMA) time-series of interferometric observations of the quiet Sun obtained at 3 mm with a 2-s cadence and a spatial resolution of a few arcsec. The same analysis, over the same fields of view and for the same intervals, was performed for simultaneous Atmospheric Imaging Assembly (AIA) image sequences in 1600 Å. Spatially-resolved chromospheric oscillations at 3 mm, with frequencies of 4.2 +- 1.7 mHz are observed in the quiet Sun, in both cell and network. The coherence length-scale of the oscillations is commensurate with the spatial resolution of our ALMA observations. Brightness-temperature fluctuations in individual pixels could reach up to a few hundred K, while the spatially averaged power spectral densities yield rms in the range ~ 55-75 K, i.e., up to ~ 1 % of the averaged brightness temperatures and exhibit a moderate increase towards the limb. For AIA 1600 A, the oscillation frequency is 3.7 +- 1.7 mHz. The relative rms is up to 6 % of the background intensity, with a weak increase towards disk center (cell, average). ALMA 3 mm time-series lag AIA 1600 Å by ~ 100 s, which corresponds to a formation-height difference of ~ 1200 km. The ALMA oscillations that we detected exhibit higher amplitudes than those derived from the lower (~ 10 arcsec) resolution observations at 3.5 mm by White et al. (2006). Chromospheric oscillations are, therefore, not fully resolved at the length-scale of the chromospheric network, and possibly not even at the spatial resolution of our ALMA observations. Any study of transient brightenings in the mm-domain should take into account the oscillations.
Authors: S. Patsourakos, C. A. Alissandrakis, A. Nindos, T. S. Bastian
Projects: ALMA
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Publication Status: A&A, in press
Last Modified: 2019-12-18 10:01
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Evidence for two-loop interaction from IRIS and SDO observations of penumbral brightenings |
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Spiros Patsourakos Submitted: 2017-04-26 04:56
We analyzed spectral and imaging data from the Interface Region Imaging Spectrograph (IRIS), images from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO), and magnetograms from the Helioseismic and Magnetic Imager (HMI) aboard SDO. We report observations of small flaring loops in the penumbra of a large sunspot on July 19, 2013. Our main event consisted of a loop spanning ~ 15 arcsec, from the umbral-penumbral boundary to an opposite polarity region outside the penumbra. It lasted approximately 10 minutes with a two minute impulsive peak and was observed in all AIA/SDO channels, while the IRIS slit was located near its penumbral footpoint. Mass motions with an apparent velocity of ~ 100 km s-1 were detected beyond the brightening, starting in the rise phase of the impulsive peak; these were apparently associated with a higher-lying loop. We interpret these motions in terms of two-loop interaction. IRIS spectra in both the C II and Si IV lines showed very extended wings, up to about 400 km s-1, first in the blue (upflows) and subsequently in the red wing. In addition to the strong lines, emission was detected in the weak lines of Cl I, O I and C I as well as in the Mg II triplet lines. Absorption features in the profiles of the C II doublet, the Si IV doublet and the Mg h and k lines indicate the existence of material with a lower source function between the brightening and the observer. We attribute this absorption to the higher loop and this adds further credibility to the two-loop interaction hypothesis. We conclude that the absorption features in the C II, Si IV and Mg II profiles originate in a higher-lying, descending loop; as this approached the already activated lower-lying loop, their interaction gave rise to the impulsive peak, the very broad line profiles and the mass motions.
Authors: C. E. Alissandrakis, A. Koukras, S. Patsourakos, A. Nindos
Projects: IRIS
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Publication Status: 2017, Astronomy and Astrophysics, in press
Last Modified: 2017-04-26 12:02
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Microwave and EUV Observations of an Erupting Filament and Associated Flare and CME |
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Spiros Patsourakos Submitted: 2013-09-14 05:11
A filament eruption was observed with the Siberian Solar Radio Telescope (SSRT) on June 23 2012, starting around 06:40 UT, beyond the West limb. The filament could be followed in SSRT images to heights above 1 Rs, and coincided with the core of the CME, seen in LASCO C2 images. We discuss briefly the dynamics of the eruption: the top of the filament showed a smooth acceleration up to an apparent velocity of 1100 km s-1. Images behind the limb from STEREO-A show a two ribbon flare and the interaction of the main filament, located along the primary neutral line, with an arch-like structure, oriented in the perpendicular direction. The interaction was accompanied by strong emission and twisting motions. The microwave images show a low temperature component, a high temperature component associated with the interaction of the two filaments and another high temperature component apparently associated with the top of flare loops. We computed the differential emission measure from the high temperature AIA bands and from this the expected microwave brightness temperature; for the emission associated with the top of flare loops the computed brightness was 35% lower than the observed.
Authors: Alissandrakis, C. E.; Kochanov, A. A.; Patsourakos, S.; Altyntsev, A. T.; Lesovoi, S. V.; Lesovoya, N. N.
Projects: None
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Publication Status: PASJ, Oct 2013, in press
Last Modified: 2013-09-14 17:27
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Hot coronal loops associated with umbral brightenings |
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Spiros Patsourakos Submitted: 2013-08-05 20:03
Aims: We aim to investigate the association of umbral brightenings with coronal structures.
Methods: We analyzed AIA/SDO high-cadence images in all bands, HMI/SDO data, soft X-ray images from SXI/GOES-15, and Hα images from the GONG network.
Results: We detected umbral brightenings that were visible in all AIA bands as well as in Hα. Moreover, we identified hot coronal loops that connected the brightenings with nearby regions of opposite magnetic polarity. These loops were initially visible in the 94 Å band, subsequently in the 335 Å band, and in one case in the 211 Å band. A differential emission measure analysis revealed plasma with an average temperature of about 6.5 ? 106 K. This behavior suggests cooling of impulsively heated loops.
Authors: Alissandrakis, C. E.; Patsourakos, S.
Projects: SDO-AIA
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Publication Status: Astronomy & Astrophysics, 2013, Volume 556, id.A79, 5 pp
Last Modified: 2013-08-06 14:53
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On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode (Invited Review) |
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Spiros Patsourakos Submitted: 2012-05-19 01:29
A major, albeit serendipitous, discovery of the SOlar and Heliospheric Observatory mission was the observation by the Extreme Ultraviolet Telescope (EIT) of large-scale extreme ultraviolet (EUV) intensity fronts propagating over a significant fraction of the Sun's surface. These so-called EIT or EUV waves are associated with eruptive phenomena and have been studied intensely. However, their wave nature has been challenged by non-wave (or pseudo-wave) interpretations and the subject remains under debate. A string of recent solar missions has provided a wealth of detailed EUV observations of these waves bringing us closer to resolving the question of their nature. With this review, we gather the current state-of-the-art knowledge in the field and synthesize it into a picture of an EUV wave driven by the lateral expansion of the CME. This picture can account for both wave and pseudo-wave interpretations of the observations, thus resolving the controversy over the nature of EUV waves to a large degree but not completely. We close with a discussion on several remaining open questions in the field of EUV waves research.
Authors: S. Patsourakos, A. Vourlidas
Projects: None
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Publication Status: Solar Physics, 2012, On-line first
Last Modified: 2012-05-20 08:22
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The Genesis of an Impulsive Coronal Mass Ejection observed at Ultra-High Cadence by AIA on SDO |
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Spiros Patsourakos Submitted: 2010-10-28 11:23
The study of fast, eruptive events in the low solar corona is one of the science objectives of the Atmospheric Imaging Assembly (AIA) imagers on the recently launched Solar Dynamics Observatory (SDO), which take full disk images in ten wavelengths with arcsecond resolution and 12 sec cadence. We study with AIA the formation of an impulsive coronal mass ejection (CME) which occurred on June 13, 2010 and was associated with an M1.0 class flare. Specifically, we analyze the formation of the CME EUV bubble and its initial dynamics and thermal evolution in the low corona using AIA images in three wavelengths (171, 193 and 211 A). We derive the first ultra-high cadence measurements of the temporal evolution of the CME bubble aspect ratio (=bubble-height/bubble-radius). Our main result is that the CME formation undergoes three phases: it starts with a slow self-similar expansion followed by a fast but short-lived (~ 70 sec) period of strong lateral over-expansion which essentially creates the CME. Then the CME undergoes another phase of self-similar expansion until it exits the AIA field of view. During the studied interval, the CME height-time profile shows a strong, short-lived, acceleration followed by deceleration. The lateral overexpansion phase coincides with the deceleration phase. The impulsive flare heating and CME acceleration are closely coupled. However, the lateral overexpansion of the CME occurs during the declining phase and is therefore not linked to flare reconnection. In addition, the multi-thermal analysis of the bubble does not show significant evidence of temperature change.
Authors: S. Patsourakos, A. Vourlidas, G. Stenborg
Projects: None
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Publication Status: ApJL 2010, in press. Movies available at http://dl.dropbox.com/u/3971111/movies_aia_cme.tar.gz.
Last Modified: 2010-10-30 01:51
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Toward understanding the early stages of an impulsively accelerated coronal mass ejection |
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Spiros Patsourakos Submitted: 2010-08-09 08:03
The expanding magnetic flux in coronal mass ejections (CMEs) often forms a cavity. A spherical model is simultaneously fit to STEREO EUVI and COR1 data of an impulsively accelerated CME on 25 March 2008, which displays a well-defined extreme ultraviolet (EUV) and white-light cavity of nearly circular shape already at low heights ~ 0.2 Rs. The center height h(t) and radial expansion r(t) of the cavity are obtained in the whole height range of the main acceleration. We interpret them as the axis height and as a quantity proportional to the minor radius of a flux rope, respectively. The three-dimensional expansion of the CME exhibits two phases in the course of its main upward acceleration. From the first h and r data points, taken shortly after the onset of the main acceleration, the erupting flux shows an overexpansion compared to its rise, as expressed by the decrease of the aspect ratio from k=h/r ~ 3 to k ~ (1.5-2.0). This phase is approximately coincident with the impulsive rise of the acceleration and is followed by a phase of very gradual change of the aspect ratio (a nearly self-similar expansion) toward k ~ 1.5 at h ~ 10 Rs. The initial overexpansion of the CME cavity can be caused by flux conservation around a rising flux rope of decreasing axial current and by the addition of flux to a growing, or even newly forming,flux rope by magnetic reconnection. Further analysis will be required to decide which of these contributions is dominant. The data also suggest that the horizontal component of the impulsive cavity expansion (parallel to the solar surface) triggers the associated EUV wave, which subsequently detaches from the CME volume.
Authors: S. Patsourakos, A. Vourlidas, B. Kliem
Projects: STEREO
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Publication Status: A&A, 2010, in press
Last Modified: 2010-08-09 08:03
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What is the Nature of EUV Waves? First STEREO 3D Observations and Comparison with Theoretical Models |
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Spiros Patsourakos Submitted: 2009-05-18 08:18
One of the major discoveries of the Extreme ultraviolet Imaging
Telescope (EIT) on SOHO were intensity enhancements propagating over
a large fraction of the solar surface. The physical origin(s) of
the so-called `EIT' waves is still strongly debated. They are
considered to be either wave (primarily fast-mode MHD waves) or
non-wave (pseudo-wave)
interpretations. The difficulty in understanding the nature of EUV
waves lies with the limitations of the EIT observations which have
been used almost exclusively for their study. They suffer from low
cadence, and single temperature and viewpoint coverage. These
limitations are largely overcome by the SECCHI/EUVI observations
on-board the STEREO mission. The EUVI telescopes provide
high cadence, simultaneous multi-temperature coverage, and two
well-separated viewpoints. We present here the first detailed
analysis of an EUV wave observed by the EUVI disk imagers on
December 07, 2007 when the STEREO spacecraft separation was approx
45°. Both a small flare and a CME were associated with the
wave. We also offer the first comprehensive comparison of the
various wave interpretations against the observations. Our major
findings are: (1) high-cadence (2.5 min) 171AA, images showed a
strong association between expanding loops and the wave onset and
significant differences in the wave appearance between the two
STEREO viewpoints during its early stages; these differences largely
disappeared later, (2) the wave appears at the active region
periphery when an abrupt disappearance of the expanding loops occurs
within an interval of 2.5 minutes, (3) almost simultaneous images at
different temperatures showed that the wave was most visible in the
1-2 MK range and almost invisible in chromospheric/transition region
temperatures, (4) triangulations of the wave indicate it was
rather low-lying (approx90 Mm above the surface), (5)
forward-fitting of the corresponding CME as seen by the COR1
coronagraphs showed that the projection of the best-fit model on the
solar surface was not consistent with the location and size of the
co-temporal EUV wave and (6) simulations of a fast-mode wave were
found in a good agreement with the overall shape and location of the
observed wave. Our findings give significant support for a fast-mode
interpretation of EUV waves and indicate that they are probably
triggered by the rapid expansion of the loops associated with the
CME.
Authors: Patsourakos, S.; Vourlidas, A.; Wang, Y. -M.; Stenborg, G.; Thernisien, A.
Projects: STEREO
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Publication Status: Sol Phys, 2009, Special STEREO Issue, in press
Last Modified: 2009-05-18 08:23
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Subject will be restored when possible |
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Spiros Patsourakos Submitted: 2008-05-01 10:42
We report on the first stereoscopic observations of polar coronal jets made by the EUVI/SECCHI imagers on board the twin STEREO spacecraft. The significantly separated viewpoints (sim 11circ) allowed us to infer the 3D dynamics and morphology of a well-defined EUV coronal jet for the first time. Triangulations of the jet's location in simultaneous image pairs led to the true 3D position and thereby its kinematics. Initially the jet ascends slowly at approx10-20 mathrm{{km} {s}-1} and then, after an apparent 'jump' takes place, it accelerates impulsively to velocities exceeding 300 mathrm{{km} {s}-1} with accelerations exceeding the solar gravity. Helical structure is the most important geometrical feature of the jet which shows evidence of untwisting. The jet structure appears strikingly different from each of the two STEREO viewpoints: face-on in the one viewpoint and edge-on in the other. This provides conclusive evidence that the observed helical structure is real and is not resulting from possible projection effects of single viewpoint observations. The clear demonstration of twisted structure in polar jets compares favorably with synthetic images from a recent MHD simulation of jets invoking magnetic untwisting as their driving mechanism. Therefore, the latter can be considered as a viable mechanism for the initiation of polar jets.
Authors: Patsourakos, S., Pariat, E. Vourlidas, A., Antiochos, S. K., Wuelser, J. P.
Projects: STEREO
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Publication Status: ApJL in press
Last Modified: 2008-09-23 21:02
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The Quiet Sun Network at Sub-Arcsecond Resolution: VAULT Observations and Radiative Transfer Modeling of Cool Loops |
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Spiros Patsourakos Submitted: 2007-05-02 08:58
One of the most enigmatic regions of the solar atmosphere is the
transition region (TR), corresponding to plasmas with temperatures
intermediate of the cool, few thousand K, chromosphere and the hot,
few million K, corona. The traditional view is that the TR emission
originates from a thin thermal interface in hot coronal structures,
connecting their chromosphere with their corona. This paradigm fails
badly for cool plasmas (approx T < {10}5 K) since it predicts
emission orders of magnitude less than what it is observed. It was
therefore proposed that the ''missing'' TR emission could originate
from tiny, isolated from the hot corona, cool loops at TR
temperatures. A major problem in investigating this proposal
is the very small sizes of the hypothesized cool loops. Here, we report
the first spatially resolved observations of sub-arcsec-scale loop-like
structures seen in the Ly α line made by the Very High Angular
Resolution Ultraviolet Telescope (VAULT). The sub-arcsec (approx
0.3 arcsec) resolution of VAULT allows us to directly view and
resolve loop-like structures in the quiet Sun network.
We compare the observed intensities of these structures with
simplified radiative transfer models of cool loops. The reasonable
agreement between the models and the observations indicates that
an explanation of the observed fine structure in terms of cool loops
is plausible.
Authors: S. Patsourakos, P. Gouttebroze, and A. Vourlidas
Projects: None
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Publication Status: ApJ, 2007, in press, July 20, v664n 1 issue
Last Modified: 2007-05-02 11:04
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