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Slipping Magnetic Reconnection, Chromospheric Evaporation, Implosion, and Precursors in the 2014 September 10 X1.6-Class Solar Flare  

Jaroslav Dudik   Submitted: 2016-03-22 03:29

We investigate the occurrence of slipping magnetic reconnection, chromospheric evaporation, and coronal loop dynamics in the 2014 September 10 X-class flare. The slipping reconnection is found to be present throughout the flare from its early phase. Flare loops are seen to slip in opposite directions towards both ends of the ribbons. Velocities of 20-40 km s-1 are found within time windows where the slipping is well resolved. The warm coronal loops exhibit expanding and contracting motions that are interpreted as displacements due to the growing flux rope that subsequently erupts. This flux rope existed and erupted before the onset of apparent coronal implosion. This indicates that the energy release proceeds by slipping reconnection and not via coronal implosion. The slipping reconnection leads to changes in the geometry of the observed structures at the IRIS slit position, from flare loop top to the footpoints in the ribbons. This results in variations of the observed velocities of chromospheric evaporation in the early flare phase. Finally, it is found that the precursor signatures including localized EUV brightenings as well as non-thermal X-ray emission are signatures of the flare itself, progressing from the early phase towards the impulsive phase, with the tether-cutting being provided by the slipping reconnection. The dynamics of both the flare and outlying coronal loops is found to be consistent with the predictions of the standard solar flare model in 3D.

Authors: Jaroslav Dudik, Vanessa Polito, Miho Janvier, Sargam M. Mulay, Marian Karlický, Guillaume Aulanier, Giulio Del Zanna, Elena Dzifcakova, Helen E. Mason, Brigitte Schmieder
Projects: GOES X-rays ,IRIS,SDO-AIA,SDO-HMI

Publication Status: The Astrophysical Journal, accepted
Last Modified: 2016-03-23 12:20
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KAPPA: A Package for Synthesis of optically thin spectra for the non-Maxwellian kappa-distributions based on the CHIANTI database  

Jaroslav Dudik   Submitted: 2015-02-06 01:42

The non-Maxwellian κ-distributions have been detected in the solar transition region and flares. These distributions are characterized by a high-energy tail and a near-Maxwellian core and are known to have significant impact on the resulting optically thin spectra arising from collisionally dominated astrophysical plasmas. We developed the KAPPA package (this http URL) for synthesis of such line and continuum spectra. The package is based on the freely available CHIANTI database and software, and can be used in a similar manner. Ionization and recombination rates together with the ionization equilibria are provided for a range of κ values. Distribution-averaged collision strengths for excitation are obtained by an approximate method for all transitions in all ions available within CHIANTI. The validity of this approximate method is tested by comparison with direct calculations. Typical precisions of better than 5% are found, with all cases being within 10%. Tools for calculation of synthetic line and continuum intensities are provided and described. Examples of the synthetic spectra and SDO/AIA responses to emission for the κ-distributions are given.

Authors: Dzifcakova, E., Dudik, J., Kotrc, P., Farnik, F., Zemanova, A.
Projects: None

Publication Status: ApJS, accepted
Last Modified: 2015-02-06 11:50
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On the Area Expansion of Magnetic Flux-Tubes in Solar Active Regions  

Jaroslav Dudik   Submitted: 2014-09-25 07:45

We calculated the 3D distribution of the area expansion factors in a potential magnetic field extrapolated from the high-resolution Hinode/SOT magnetogram of a quiescent active region NOAA 11482. Retaining only closed loops within the computational box, we show that the distribution of area expansion factors show significant structure. Loop-like structures characterized by locally lower values of the expansion factor are embedded in a smooth background. These loop-like flux-tubes have squashed cross-sections and expand with height. The distribution of the expansion factors show overall increase with height, allowing an active region core characterized by low values of the expansion factor to be distinguished. The area expansion factors obtained from extrapolation of the SOT magnetogram are compared to those obtained from an approximation of the observed magnetogram by a series of 134 submerged charges. This approximation retains the general flux distribution in the observed magnetogram, but removes the small-scale structure in both the approximated magnetogram and the 3D distribution of the area expansion factors. We argue that the structuring of the expansion factor can be a significant ingredient in producing the observed structuring of the solar corona. However, due to the potential approximation used, these results may not be applicable to loops exhibiting twist neither to active regions producing significant flares.

Authors: Dudik, J., Dzifcakova, E., Cirtain, J. W.
Projects: Hinode/SOT

Publication Status: The Astrophysical Journal, accepted
Last Modified: 2014-09-25 15:58
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Signatures of the non-Maxwellian kappa-distributions in optically thin line spectra I. Theory and synthetic Fe IX-XIII spectra  

Jaroslav Dudik   Submitted: 2014-09-23 08:40

We investigate the possibility of diagnosing the degree of departure from the Maxwellian distribution using single-ion spectra originating in astrophysical plasmas in collisional ionization equilibrium. New atomic data for excitation of Fe IX-XIII are integrated under the assumption of a kappa-distribution of electron energies. Diagnostic methods using lines of a single ion formed at any wavelength are explored. Such methods minimize uncertainties from the ionization and recombination rates, as well as the possible presence of non-equilibrium ionization. Approximations to the collision strengths are also investigated. The calculated intensities of most of the Fe IX-XIII EUV lines show consistent behaviour with kappa at constant temperature. Intensities of these lines decrease with kappa, with the vast majority of ratios of strong lines showing little or no sensitivity to kappa. Several of the line ratios, especially involving temperature-sensitive lines, show a sensitivity to kappa that is of the order of several tens of per cent, or, in the case of Fe IX, up to a factor of two. Forbidden lines in the near-ultraviolet, visible, or infrared parts of the spectrum are an exception, with smaller intensity changes or even a reverse behaviour with kappa. The most conspicuous example is the Fe X 6378A red line, whose intensity incerases with kappa. This line is a potentially strong indicator of departures from the Maxwellian distribution. We find it possible to perform density diagnostics independently of kappa, with many Fe XI-XIII line ratios showing strong density-sensitivity and negligible sensitivity to kappa and temperature. We also tested different averaging of the collision strengths. It is found that averaging over 0.01 interval in log(E/Ryd) is sufficient to produce accurate distribution-averaged collision strengths at temperatures of the ion formation in ionization equilibrium.

Authors: Dudik, J, Del Zanna, G., Mason, H.E., Dzifcakova, E.
Projects: Hinode/EIS

Publication Status: to appear in Astronomy & Astrophysics
Last Modified: 2014-09-23 10:49
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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-1 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 evolution of magnetic structures in the ``standard solar flare model in 3D''. This model matches the observations well, reproducing both the apparently slipping flare loops, S-shaped erupting loops, and the evolution of flare ribbons. All of these processes are explained via 3D reconnection mechanisms resulting from the expansion of a torus-unstable flux rope. The AIA observations and the numerical model are complemented by radio observations showing a noise storm in the metric range. Dm-drifting pulsation structures occurring during the eruption indicate plasmoid ejection and enhancement of reconnection rate. The bursty nature of radio emission shows that the slipping reconnection is still intermittent, although it is observed to persist for more than an hour.

Authors: J. Dudik, M. Janvier, G. Aulanier, G. Del Zanna, M. Karlický, H. Mason, B. Schmieder
Projects: SDO-AIA

Publication Status: The Astrophysical Journal, accepted
Last Modified: 2014-01-30 10:51
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Magnetic Topology of Quiescent Prominence Bubbles  

Jaroslav Dudik   Submitted: 2012-10-18 13:10

We study a polar-crown prominence with a bubble and its plume observed in several coronal filters by the SDO/AIA and in Hα by the MSDP spectrograph in Bialkow (Poland) to address following questions: What is the brightness of prominence bubbles in EUV with respect to corona outside of the prominence and the prominence coronal cavity? What is the geometry and topology of magnetic field in the bubble? What is the nature of vertical threads seen within prominences? We find that the brightness of the bubble and plume is lower than the brightness of the corona outside of the prominence, and is similar to that of the coronal cavity. We constructed linear force-free models of the prominences with bubbles, where the flux rope is perturbed by inclusion of parasitic bipoles. The arcade field lines of the bipole create the bubble, which is thus devoid of magnetic dips. Shearing the bipole or adding a second one can lead to cusp-shaped prominences with bubbles similar to the observed ones. The bubbles have complex magnetic topology, with a pair of coronal magnetic null-points linked by a separator outlining the boundary between the bubble and the prominence body. We conjecture that plume formation involve magnetic reconnection at the separator. Depending on the viewing angle, the prominence can appear either anvil-shaped with predominantly horizontal structures, or cusp-shaped with predominantly vertical structuring. The latter is an artefact of the alignment of magnetic dips with respect to the prominence axis and the line of sight.

Authors: Dudik J., Aulanier G., Schmieder B., Zapior M., Heinzel P.
Projects:

Publication Status: ApJ, accepted
Last Modified: 2012-10-24 12:45
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The non-Maxwellian continuum in the X-ray, UV, and radio range  

Jaroslav Dudik   Submitted: 2012-03-06 02:24

Aims: We investigate the X-ray, UV, and also the radio continuum arising from plasmas with a non-Maxwellian distribution of electron energies. The two investigated types of distributions are the kappa- and n-distributions. Methods: We derived analytical expressions for the non-Maxwellian bremsstrahlung and free-bound continuum spectra. The spectra were calculated using available cross-sections. Then we compared the bremsstrahlung spectra arising from the different bremsstrahlung cross-sections that are routinely used in solar physics. Results: The behavior of the bremsstrahlung spectra for the non-Maxwellian distributions is highly dependent on the assumed type of the distribution. At flare temperatures and hard X-ray energies, the bremsstrahlung is greatly increased for kappa-distributions and exhibits a strong high-energy tail. With decreasing kappa, the maximum of the bremsstrahlung spectrum decreases and moves to higher wavelengths. In contrast, the maximum of the spectra for n-distributions increases with increasing n, and the spectrum then falls off very steeply with decreasing wavelength. In the millimeter radio range, the non-Maxwellian bremsstrahlung spectra are almost parallel to the thermal bremsstrahlung. Therefore, the non-Maxwellian distributions cannot be detected by off-limb observations made by the ALMA instrument. The free-bound continua are also highly dependent on the assumed type of the distribution. For n-distributions, the ionization edges disappear and a smooth continuum spectrum is formed for n ≧ 5. Opposite behavior occurs for kappa-distributions where the ionization edges are in general significantly enhanced, with details depending on kappa and T through the ionization equilibrium. We investigated how the non-Maxwellian kappa-distributions can be determined from the observations of the continuum and conclude that one can sample the low-energy part of the distribution from the continuum.

Authors: Dudík, J., Ka?parov?, J., Dzifčáková, E., Karlický, M., Mackovjak, ?.
Projects: None

Publication Status: Astronomy & Astrophysics, Vol. 539, A107
Last Modified: 2012-03-07 09:06
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On the physical meaning of n-distributions in solar flares  

Jaroslav Dudik   Submitted: 2012-02-28 09:36

Aims. We investigate the physical meaning of the n-distributionsdetected in solar flares.
Methods. We consider a Maxwellian velocity distribution with avelocity drift. This distribution is analytically integrated to obtainthe energy distribution, and its stability is investigated numericallyusing a fully electromagnetic particle-in-cell code.
Results. It is shown that the derived moving Maxwellian energydistribution is very similar to the n-distribution, especially in theirhigh-energy parts. Both these distributions are mutually fitted and arelation between their parameters found. Contrary to the ndistribution,the moving Maxwellian distribution has a simple physical meaning,e.g., the electron component of the return currentin the beam-plasma system. However, for high drift velocities of sucha component, the moving Maxwellian distribution is unstable.Therefore to keep the form of this distribution similar to then-distribution, some stabilization processes are necessary. If so, thenthe high intensities of the Si XIId 5.56A and 5.82A satellite linesand their evolution in solar flares can be explained by movingMaxwellian distributions instead of the n-distributions. Thus, ourprevious results connected with the n-distributions can be understoodin a new, physically profound way.

Authors: Karlický, M., Dzifcakova, E., Dudik, J.
Projects: None

Publication Status: Astronomy & Astrophysics, Vol. 537, A36
Last Modified: 2012-02-29 08:25
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Subject will be restored when possible  

Jaroslav Dudik   Submitted: 2008-01-08 03:49

We study the topology of the 3D magnetic field in a filament channel to address the following questions: Is a filament always formed in a single flux tube? How does the photospheric magnetic field lead to filament interruptions and to feet formation? What is the relation between feet-related field lines and the parasitic polarities? What can topological analyzes teach us about EUV filament channels? To do so, we consider a filament observed on October 6th, 2004 with THEMIS/MTR, in Hα with the full line profile simulatenously and cospatially with its photospheric vector magnetic field. The coronal magnetic field was calculated from a `linear magneto-hydrostatic' extrapolation of a composite THEMIS-MDI magnetogram. Its free parameters were adujsted to get the best match possible between the distribution of modeled plasma-supporting dips and the Hα filament morphology. The model results in moderate plasma beta < 1 at low altitudes in the filament, in conjunction with non-negligible departures from force-freeness measured by various metrics. The filament here is formed by a splitted flux tube. One part of the flux tube is rooted in the photosphere aside an observed interruption in the filament. This splitted topology is due to strong network polarities on the edge of the filament channel, not to flux concentrations closer to the filament. We focus our study to the North-West portion of the filament. The related flux tube is highly fragmented at low altitudes. This fragmentation is due to small flux concentrations of two types. First, some locally distort the tube, leading to noticeable thickness variations along the filament body. Second, parasitic polarities, associated with filament feet, result in secondary dips above the related local inversion line. These dips belong to long field lines which pass below the flux tube. Many of these field lines are not rooted nearby the related foot. Finally, the present model shows that the coronal void interpretation cannot be ruled out to interprete the wideness of EUV filament channels.

Authors: Dudik, J., Aulanier, G., Schmieder, B., Bommier, V., Roudier, T.
Projects: Dutch Open Telescope,SoHO-MDI,TRACE

Publication Status: SoPh (accepted)
Last Modified: 2008-01-08 07:37
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Subject will be restored when possible  

Jaroslav Dudik   Submitted: 2008-01-08 03:49

We study the topology of the 3D magnetic field in a filament channel to address the following questions: Is a filament always formed in a single flux tube? How does the photospheric magnetic field lead to filament interruptions and to feet formation? What is the relation between feet-related field lines and the parasitic polarities? What can topological analyzes teach us about EUV filament channels? To do so, we consider a filament observed on October 6th, 2004 with THEMIS/MTR, in Hα with the full line profile simulatenously and cospatially with its photospheric vector magnetic field. The coronal magnetic field was calculated from a `linear magneto-hydrostatic' extrapolation of a composite THEMIS-MDI magnetogram. Its free parameters were adujsted to get the best match possible between the distribution of modeled plasma-supporting dips and the Hα filament morphology. The model results in moderate plasma beta < 1 at low altitudes in the filament, in conjunction with non-negligible departures from force-freeness measured by various metrics. The filament here is formed by a splitted flux tube. One part of the flux tube is rooted in the photosphere aside an observed interruption in the filament. This splitted topology is due to strong network polarities on the edge of the filament channel, not to flux concentrations closer to the filament. We focus our study to the North-West portion of the filament. The related flux tube is highly fragmented at low altitudes. This fragmentation is due to small flux concentrations of two types. First, some locally distort the tube, leading to noticeable thickness variations along the filament body. Second, parasitic polarities, associated with filament feet, result in secondary dips above the related local inversion line. These dips belong to long field lines which pass below the flux tube. Many of these field lines are not rooted nearby the related foot. Finally, the present model shows that the coronal void interpretation cannot be ruled out to interprete the wideness of EUV filament channels.

Authors: Dudik, J., Aulanier, G., Schmieder, B., Bommier, V., Roudier, T.
Projects: Dutch Open Telescope,SoHO-MDI,THEMIS/MTR,TRACE

Publication Status: SoPh (accepted)
Last Modified: 2008-01-09 08:53
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Subject will be restored when possible  

Jaroslav Dudik   Submitted: 2008-01-08 03:48

We study the topology of the 3D magnetic field in a filament channel to address the following questions: Is a filament always formed in a single flux tube? How does the photospheric magnetic field lead to filament interruptions and to feet formation? What is the relation between feet-related field lines and the parasitic polarities? What can topological analyzes teach us about EUV filament channels? To do so, we consider a filament observed on October 6th, 2004 with THEMIS/MTR, in Hα with the full line profile simulatenously and cospatially with its photospheric vector magnetic field. The coronal magnetic field was calculated from a `linear magneto-hydrostatic' extrapolation of a composite THEMIS-MDI magnetogram. Its free parameters were adujsted to get the best match possible between the distribution of modeled plasma-supporting dips and the Hα filament morphology. The model results in moderate plasma beta < 1 at low altitudes in the filament, in conjunction with non-negligible departures from force-freeness measured by various metrics. The filament here is formed by a splitted flux tube. One part of the flux tube is rooted in the photosphere aside an observed interruption in the filament. This splitted topology is due to strong network polarities on the edge of the filament channel, not to flux concentrations closer to the filament. We focus our study to the North-West portion of the filament. The related flux tube is highly fragmented at low altitudes. This fragmentation is due to small flux concentrations of two types. First, some locally distort the tube, leading to noticeable thickness variations along the filament body. Second, parasitic polarities, associated with filament feet, result in secondary dips above the related local inversion line. These dips belong to long field lines which pass below the flux tube. Many of these field lines are not rooted nearby the related foot. Finally, the present model shows that the coronal void interpretation cannot be ruled out to interprete the wideness of EUV filament channels.

Authors: Dudik, J., Aulanier, G., Schmieder, B., Bommier, V., Roudier, T.
Projects: Dutch Open Telescope

Publication Status: SoPh (accepted)
Last Modified: 2008-01-08 03:48
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Abstracts by Author
Slipping Magnetic Reconnection, Chromospheric Evaporation, Implosion, and Precursors in the 2014 September 10 X1.6-Class Solar Flare
KAPPA: A Package for Synthesis of optically thin spectra for the non-Maxwellian kappa-distributions based on the CHIANTI database
On the Area Expansion of Magnetic Flux-Tubes in Solar Active Regions
Signatures of the non-Maxwellian kappa-distributions in optically thin line spectra I. Theory and synthetic Fe IX--XIII spectra
Slipping magnetic reconnection during an X-class solar flare observed by SDO/AIA
Magnetic Topology of Quiescent Prominence Bubbles
The non-Maxwellian continuum in the X-ray, UV, and radio range
On the physical meaning of n-distributions in solar flares
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Subject will be restored when possible
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