OBSERVATIONS AND ANALYSIS OF SOLAR FLARES USING HYDROGEN-ALPHA SPECTRAL PROFILES (SUN, RADIATIVE TRANSFER)

The temperature and density structure of the solar chromosphere during a flare holds a great deal of information about energetic flare processes. Since the form of the H(alpha) spectral line is very sensitive to the chromospheric temperature and density distribution, H(alpha) profile observations can help us learn about fast particles, enhanced pressure, enhanced thermal conduction, chromospheric evaporation, mass motion, and other flare effects. This dissertation approaches the chromospheric flare problem in three steps: Analysis of an observed flare using existing empirical models; development of new physical models of H(alpha); and analysis of another observed flare using these physical models.; First, the flare of 1980 May 7 is analyzed using H(alpha) spectral profiles from Sacramento Peak Observatory and cotemporal X-ray observations from the Solar Maximum Mission spacecraft. Through comparison of the observed profiles with the empirical H(alpha) profiles, it is shown that chromospheric evaporation takes place concurrently with enhancement of the overlying coronal density. During the impulsive phase, it is suggested that evaporation is driven by flare-accelerated electrons. During the thermal phase, it can only be driven by thermal conduction.; Next, physical models of H(alpha) spectral profiles are calculated for a grid of model flare chromospheres, in both the hydrostatic and impulsive approximations. It is shown that only high fluxes of nonthermal electrons produce broad, nonGaussian profile wings, and that only high values of the coronal pressure can remove the central reversal of the profiles. Enhanced thermal conduction alone cannot account for enhanced H(alpha) emission.; Finally, the flare of 1980 Jun 24 is analyzed, showing that nonthermal electrons were accelerated bidirectionally within coronal loops and injected into the chromosphere at the loop footpoints. All of the observed hard X-ray flux can be explained by nonthermal bremsstrahlung. Pressure balance is shown to exist across the transition region. Chromospheric evaporation is again shown to be adequate to provide the coronal flare plasma. The observations suggest that the energy release took place as a result of the interaction of two large magnetic loop systems.