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Non-Maxwellian analysis of the transition-region line profiles observed by the Interface Region Imaging Spectrograph  

Jaroslav Dud   Submitted: 2017-06-16 10:27

We investigate the nature of the spectral line profiles for transition region ions observed with the Interface Region Imaging Spectrograph (IRIS). In this context, we have analyzed an active-region observation performed by IRIS in its 1400 Å spectral window. The transition-region lines are found to exhibit significant wings in their spectral profiles, which can be well-fitted with non-Maxwellian kappa-distribution. The fit with a kappa-distribution can perform better than a double Gaussian fit, especially for the strongest line, Si IV 1402.8 A. Typical values of κ found are about 2, occurring in a majority of spatial pixels where the transition region lines are symmetric, i.e., the fit can be performed. Furthermore, all five spectral lines studied (from Si IV, O IV and S IV) appear to have the same FWHM irrespective of whether the line is an allowed or an intercombination transition. A similar value of kappa is obtained for the electron distribution by fitting of the line intensities relative to Si IV 1402.8 A, if photospheric abundances are assumed. The kappa-distributions however do not remove the presence of non-thermal broadening. Instead, they actually increase the non-thermal width. This is because for kappa-distributions the transition-region ions are formed at lower temperatures. The large observed non-thermal width lowers the opacity of the Si IV line sufficiently enough for this line to become optically thin.

Authors: J. Dudík, V. Polito, E. Dzifčáková, G. Del Zanna, and P. Testa
Projects: IRIS

Publication Status: The Astrophysical Journal, in press
Last Modified: 2017-06-20 16:12
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Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)  

Jaroslav Dud   Submitted: 2017-06-16 10:26

We review the presence and signatures of the non-equilibrium processes, both non-Maxwellian distributions and non-equilibrium ionization, in the solar transition region, corona, solar wind, and flares. Basic properties of the non-Maxwellian distributions are described together with their influence on the heat flux as well as on the rates of individual collisional processes and the resulting optically thin synthetic spectra. Constraints on the presence of high-energy electrons from observations are reviewed, including positive detection of non-Maxwellian distributions in the solar corona, transition region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed as well, especially in connection to hydrodynamic and generalized collisional-radiative modelling. Predicted spectroscopic signatures of non-equilibrium ionization depending on the assumed plasma conditions are summarized. Finally, we discuss the future remote-sensing instrumentation that can be used for detection of these non-equilibrium phenomena in various spectral ranges.

Authors: J. Dudík, E. Dzifčáková, N. Meyer-Vernet, G. Del Zanna, P. R. Young, A. Giunta, B. Sylwester, J. Sylwester, M. Oka, H. E. Mason, C. Vocks, L. Matteini, S. Krucker, D. R. Williams, Š. Mackovjak
Projects: None

Publication Status: Solar Physics, accepted
Last Modified: 2017-06-20 16:12
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Expanding and Contracting Coronal Loops as Evidence of Vortex Flows Induced by Solar Eruptions  

Jaroslav Dud   Submitted: 2017-06-16 10:20

Eruptive solar flares were predicted to generate large-scale vortex flows at both sides of the erupting magnetic flux rope. This process is analogous to a well-known hydrodynamic process creating vortex rings. The vortices lead to advection of closed coronal loops located at peripheries of the flaring active region. Outward flows are expected in the upper part and returning flows in the lower part of the vortex. Here, we examine two eruptive solar flares, an X1.1-class flare SOL2012-03-05T03:20 and a C3.5-class SOL2013-06-19T07:29. In both flares, we find that the coronal loops observed by the Atmospheric Imaging Assembly in its 171 Å, 193 A, or 211 Å passbands show coexistence of expanding and contracting motions, in accordance with the model prediction. In the X-class flare, multiple expanding/contracting loops coexist for more than 35 minutes, while in the C-class flare, an expanding loop in 193 Å appears to be close-by and co-temporal with an apparently imploding loop arcade seen in 171 A. Later, the 193 Å loop also switches to contraction. These observations are naturally explained by vortex flows present in a model of eruptive solar flares.

Authors: J. Dudík, F. P. Zuccarello, G. Aulanier, B. Schmieder, P. Démoulin
Projects: SDO-AIA

Publication Status: The Astrophysical Journal, accepted
Last Modified: 2017-06-20 16:13
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Abstracts by Author
Non-Maxwellian analysis of the transition-region line profiles observed by the Interface Region Imaging Spectrograph
Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)
Expanding and Contracting Coronal Loops as Evidence of Vortex Flows Induced by Solar Eruptions

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MSU Solar Physics.
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