A STUDY OF SOLAR-FLARE ENERGY-TRANSPORT BASED ON COORDINATED H-ALPHA AND X-RAY OBSERVATIONS

Coordinated H-alpha, hard X-ray (HXR), and soft X-ray observations of five solar flares allow us to determine, for the first time, the temporal variation of the ratio of H-alpha to nonthermal hard X-ray emissions, and to compare its behavior to the predictions of a hydrostatic one-dimensional thick-target nonthermal electron model of solar flare energy transport. We have used the observations to estimate the emitted flare energy flux F(H)-alpha in H-alpha, the flux of energy F-20 deposited by nonthermal electrons with energies above 20 keV, and the pressure p(c) of soft X-ray emitting plasma as functions of time during the impulsive phase of each flare. The F(H)-alpha/F-20 ratio show a power-law dependence on F-20 of the form F(H)-alpha/F-20 proportional F-20-(0.7 +/- 0.1). Analyzing the observations with the thick-target model, we demonstrate that: (1) the power-law dependence of the F(H)-alpha/F-20 ratio on F-20 is consistent with that predicted by the model if the nonthermal electron precipitation area does not vary by more than a factor of five during the impulsive phase of the observed flares; (2) there is evidence for modification of the power-law dependence by hydrostatic pressure effects; (3) the observed magnitude of the F(H)-alpha/F-20 ratio implies a small precipitation area of approximately 10(17) cm2 and correspondingly large beam fluxes (approximately 10(12) ergs cm-2 s-1 for all five flares.