A&A Supplement series, Vol. 127, February I 1998, 607-618
Received July 29; accepted May 27, 1997
T. Nejezchleba
Send offprint request: T. Nejezchleba
Astronomical Institute, Academy of Sciences of the Czech
Republic, CZ-25165 Ondrejov, Czech Republic
A method of calculating NLTE models of a plan-parallel solar flare
atmosphere with stationary plasma flows is presented. To solve
the radiative transfer equation, equations of statistical
equilibrium (ESE) and the stationary momentum equation, we use the
multilevel approximate lambda iteration (MALI) approach. The
numerical code is based on the
method recently developed by Rybicky & Hummer (1991, 1992) and
allows to take into account macroscopic velocity fields in
observer's frame formulation. The
preconditioned ESE, constructed by this method, are finally
linearized with respect to level populations and electron
densities to treat the the hydrogen ionization balance.
The numerical code based on this method is used to compute a grid of
NLTE flare models with various velocity fields in order to show the influence
of the velocity fields on the 
-line asymmetries.
The analysis of the results lead to conclusions that would improve interpretations of flare line asymmetries: 1) The velocities affect the level populations, 2) The type of asymmetry depends on the changes in the optical depth scales and on the run of the source function in the atmosphere. 3) A monotonous velocity affects only one wing of the line profile. 4) To get the velocity field from an observed profile the bisector method should be modified.
keywords: line: formation -- line: profiles -- radiative transfer -- methods: numerical -- Sun: flares