Ultraviolet Flare Studies

Abstract

A comprehensive understanding of the complicated physical processes that occur in solar active regions and flares requires observations covering a wide wavelength range from radio to hard X-rays. In the last two decades, analyses of the XUV and soft X-ray observations, obtained mainly from Skylab and P78-1 have increased greatly our knowledge about the morphological and dynamic developments of the soft X-ray bursts in the flare gradual phase (cf. Cheng and Widing 1975; Pallavicini, Serio and Vaiana 1977; Moore et al. 1980; Doschek et al. 1980). On the other hand, we know comparatively little about the physical conditions in the plasmas in which impulsive UV and hard X-ray bursts originate. This is partly due to the lack of sufficient spatial resolution and complete time coverage for the hard X-ray and UV observations. In addition, the lack of available direct physical diagnostics of the hard X-rays have combined with the above shortcomings to leave many fundamental questions about the nature of the impulsive phase largely unanswered.