A CHROMOSPHERIC RESPONSE TO PULSE BEAM HEATING

Starting from the new flare models of Karlicky (1990) and Karlicky and Henoux (1991), we present here the first time-dependent numerical simulations of hydrogen plasma excitation and ionization on time scales of less than one second. These time scales are consistent with the spiky behaviour of the kinetic temperature produced by non-thermal collisional processes. Such temperature spikes represent a chromospheric response to a series of short-duration electron beam pulses which are supposed to heat the flare atmosphere. Self-consistent numerical solution of a simplified, time-dependent, non-LTE problem for a three-level hydrogen atom model with continuum allows us to predict theoretically a qualitative behaviour of the H-alpha line intensity variations on very short time intervals. Our H-alpha temporal profiles, evaluated at the line center and for DELTA-lambda = 1 angstrom, can be qualitatively compared with some recent flare observations obtained with high temporal resolution.