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.
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
Soft X-ray heating of the solar chromosphere during the gradual phase of two solar flares
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
Publication Status: Published
Last Modified: 2004-07-26 07:27