QUANTITATIVE-EVALUATION OF THE SOLAR-FLARE MORPHOLOGY IN HARD X-RAYS USING THE YOHKOH HXT

To quantitfy the hard X-ray morphology of solar flares observed with t he Yohkoh HXT (Hard X-ray Telescope), a quantity named Configurational Difference Measure (CDM) was introduced. In terms of a single scalar value, CDM measures the difference between two X-ray brightness distri butions specified by two data sets from the same flare, separated eith er in time or in energy. It has been shown that CDM can sensitively qu antify the time evolution and energy dependence of the spatial structu re of flare hard X-ray sources, with several advantages over the Maxim um Entropy Method (MEM). An analysis of a sample of eleven flares empl oying CDM confirmed a close relationship among the light curve, spectr um, and morphology of flare hard X-rays. The early phase of a flare is generally characterized by impulsive lightcurves, hard power-law spec tra, and multiple bright spots suggestive of loop footpoints. In the l ate phase, a flare tends to show gradual lightcurves, softer spectra, and a loop-like morphology. These properties as revealed with CDM are discussed in terms of thermal and nonthermal mechanisms.