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Observations and Modeling of Line Asymmetries in Chromospheric Flares  

Arkadiusz Berlicki   Submitted: 2007-03-30 06:00

For many years various asymmetrical profiles of different spectral lines emitted from solar flares have been frequently observed. These asymmetries or line shifts are caused predominantly by vertical mass motions in flaring layers and they provide a good diagnostics for plasma flows during solar flares. There are many controversial results of observations and theoretical analysis of plasma flows in solar chromospheric flares. The main difficulty is the interpretation of line shifts or asymmetries. For many years, methods based on bisector techniques were used but they give a reliable results only for some specific conditions and in most cases cannot be applied. The most promising approach is to use the non-LTE techniques applied for flaring atmosphere. The calculation of synthetic line profiles is performed with the radiative transfer techniques and the assumed physical conditions correspond to flaring atmosphere. I will present an overview of different observations and interpretations of line asymmetries in chromospheric flares. I will explain what we have learnt about the chromospheric evaporation in the frame of hydrodynamical models as well as reconnection models. A critical review will be done on the classical methods used to derive Doppler-shifts for optically thick chomospheric lines. In particular, details on the new approach for interpreting chromospheric line asymmetries based on the non-LTE techniques will be presented.

Authors: Berlicki, A.
Projects: None

Publication Status: Proceedings of the Coimbra Solar Physics Meeting: 'THE PHYSICS OF CHROMOSPHERIC PLASMAS', Coimbra, Portugal, 9-13 October 2006, ASP Series, Vol. 368 - in press
Last Modified: 2007-03-30 09:15
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Soft X-ray heating of the solar chromosphere during the gradual phase of two solar flares  

Arkadiusz Berlicki   Submitted: 2004-07-26 07:27

In this paper we perform an analysis of the energetics of the solar flaring chromosphere irradiated by soft X-rays (SXR) emitted from overlying hot flare loops. To study an expected SXR heating we used the observations of two solar flares obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph attached to the Large Coronagraph of the Wroclaw University. SXR observations of these flares come from the Yohkoh SXR telescope (SXT). From MSDP spectral images we derived mean Hα line profiles which were then used to construct semi-empirical non-LTE models of the chromosphere in the analyzed areas of flares. On the basis of SXR observations we calculated the mean emission measure EM and the temperature in flaring coronal structures located above the Hα kernels under study and these two quantities were used to compute the SXR irradiation of the chromosphere between 1-300 ang. For each flare model we then evaluated the energy deposit due to such irradiation and compared it with the net radiative cooling rates at all depths in the chromosphere. By means of such modelling we were able to demonstrate that the enhanced emission of selected Hα kernels observed during the gradual phase of these two solar flares cannot be explained in terms of the SXR heating of the chromosphere. We found that radiative losses in all layers of the chromosphere exceeded the amount of the energy deposited by the SXR radiation. However, for stronger flares with much enhanced EM a certain contribution of SXR to the heating cannot be ruled out.

Authors: A. Berlicki, P. Heinzel
Projects: None

Publication Status: Published
Last Modified: 2004-07-26 07:27
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Observations and Modeling of Line Asymmetries in Chromospheric Flares
Soft X-ray heating of the solar chromosphere during the gradual phase of two solar flares

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