Physical conditions in the chromosphere of a two-ribbon solar flare accompanied by a surge: 1

Abstract

We studied changes in thermodynamic parameters of the chromosphere at the initial stage of the two ribbon solar flare accompanied by a surge that occurred on September 4, 1990. The inho mogeneous semiempirical models of the flare chromosphere and surge are constructed for four obser vation moments. The spectra were obtained with the ATsU 26 horizontal solar telescope of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine (Terskol Peak). Photo metric transections of the spectra passed through two bright kernels of one of the flare ribbons and through the surge. The comparison of the observed profiles of the line H α in the solar active and quiet Sun regions reveals the substantial emission in the line wings (up to 1-1.2 nm) with a residual intensity of 0.6-0.77 at the center of the line profiles. Calculations within the two component models of the chromosphere have shown that this may be the evidence of the existence of the details (unresolved by the telescope and occupying 5-12% of the total area) with a deep heating of the chromosphere layers. A strong asymmetry of the line profiles and the shift with respect to the line profile for the quiet Sun region are explained by peculiarities of the line of sight velocity distribution over the height. It is found that the motion is directed to the observer in the upper chromosphere (10-30 km/s) and from the observer in the lower chromosphere (5-20 km/s) for the larger part of the active region under study. According to the models calculated for the surge, the line of sight velocities reach a value of 70 km/s.