On Thermal Hydrodynamical Model of Solar Flares

Abstract

The existing hydrodynamical models of solar flares predict a predominantly blueshifted emission of the CaXIX w line at the early phase of the flare. The theoretical blueshift is as large as 3 to 6 mA(e.g., Gan et al. 1992). However, observations from previous missions showed that, except for a few flares in which blueshifted Ca XIX emission dominates, the Ca XIX w line exhibits more commonly blue-asymmetric line profile, with the stationary component much stronger than the blueshifted component (e.g., Doschek 1990). Recent observations obtained by the Bragg Crystal Spectrometer (BCS) on Yohkoh, with higher temporal resolution and sensitivity, have shown that most flares exhibit blueshifted Ca XIX and Fe XXV lines before and during the corresponding hard X-ray burst in the rise phase of the flares (e.g., Cheng, Rilee, & Uchida 1994). In addition, there are a few flares that show downward mass motion manifested as redshifted Ca XIX lines (e.g., Mariska, Doschek, & Bentley 1993). To account for the newly observed behavior of Ca XIX and Fe XXV emissions, it is appropriate to make some refinements of the hydrodynamical models, with different parameters, such as loop geometry, heating function, initial atmospheric state, and the effects of two or three dimension transportation. In this paper, we investigate the effects of a high coronal density in the initial model atmosphere for a thermal hydrodynamical model.