SOFT-X-RAY SPECTROSCOPY OF SOLAR-FLARES - AN OVERVIEW

In this paper, I give an overview of the current status of high spectral resolution soft X-ray observations of solar flares. The review concentrates primarily on recent results and interpretations of results obtained from orbiting Bragg crystal spectrometers flown during the last solar maximum on the US Department of Defense P78-1 spacecraft, the National Aeronautics and Space Administration Solar Maximum Mission, and the Japanese Institute of Space and Astronautical Science Hinotori spacecraft. Results and several key issues regarding interpretation of the spectra are presented. Specifically, the dynamics of coronal flare plasmas as revealed by X-ray line profiles and wavelength shifts are discussed. Recent results concerning the theory of chromospheric evaporation are given. The temperature of coronal flare plasma is discussed within the context of a differential emission measure. Results concerning electron density measurements, nonequilibrium processes, and relative element abundances are also reviewed. The paper ends with suggestions for possible future X-ray spectroscopy instrumentation.