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

Abstract

Based on spectral observations using an ATsU-26 horizontal solar telescope (Elbrus Region, Terskol Peak Observatory, 3100 m), the modeling of a two-ribbon chromospheric flare accompanied by a surge on September 4, 1990, is carried out. Semiempirical models were calculated for three moments of the initial phase of the flare at the stage of gradually growing soft X-ray radiation. Variations of the plasma physical parameters in different parts of the surge (at the center and at the edge) and the emission kernels of the flare onto which the surge is projected are studied. The modeling was carried out with the help of two- or three-component chromospheric models by matching the observed and calculated line profiles. Additional components of the models with the filling factors from 2 to 15% were necessary for explaination of the significant emission in the wings of Hα line. The calculations have shown that the temperature in the lower chromospheric layers is by 1000–3500 K higher than the temperature of the quiet Sun (VAL-C model). The line-of-sight velocities are determined that explain the observed features in the asymmetry profiles. In most of the models, the substance in the lower and upper chromosphere moves towards the observer. In the upper chromosphere, the velocities are varied from −100 to −15 km/s, while they do not exceed −40 km/s in the lower chromosphere. In some periods of time, the velocity in the central part of the surge in the middle chromosphere reached a value of 15 km/s from the observer. Additional components demonstrate the presence of oppositely directed flows with velocities ranging from −100 km/s (to the observer) to 160 km/s (from the observer).