TESTING THE IMPULSIVENESS OF SOLAR-FLARE HEATING THROUGH ANALYSIS OF DYNAMIC ATMOSPHERIC RESPONSE

One crucial test of a solar flare energy transport model is its abilit y to reproduce the characteristics of the atmospheric motions inferred from soft X-ray line spectra. Using a recently developed diagnostic, the velocity differential emission measure (VDEM), we can obtain from observations a physical measure of the amount of soft X-ray-emitting p lasma flowing at each velocity, upsilon, and hence the total momentum of the upflowing plasma, without approximation or parametric fitting. We have correlated solar hard X-ray emission profiles by the Yohkoh Ha rd X-ray telescope with the mass and momentum histories inferred from soft X-ray line profiles observed by the Yohkoh Bragg crystal spectrom eters. For suitably impulsive hard X-ray emission, an analysis of the hydrodynamic equations predicts a proportionality between the hard X-r ay intensity and the second time derivative of the soft X-ray-emitting plasma's momentum. This relationship is borne out by an analysis of 1 8 disk-center impulsive flares of varying durations, thereby lending s upport to the hypothesis that a prompt energy deposition mechanism, su ch as an energetic electron flux, is indeed responsible for the soft X -ray response observed in the rise phase of sufficiently impulsive sol ar flares.