MOMENTUM BALANCE IN 4 SOLAR-FLARES

We combine Solar Maximum Mission soft X-ray spectra and National Solar Observatory (Sacramento Peak) Hα spectra in a study of high-speed flows during the impulsive phase of four solar flares. In all events, a blue asymmetry (indicative of upflows) was observed in the coronal Ca XIX line during the soft X-ray rise phase. In all events a red asymmetry (indicative of downflows) was observed simultaneously in chromospheric Hα. These oppositely directed flows were concurrent with impulsive hard X-ray emission. Combining the velocity data with estimates of the density based on emission measure measurements and volume estimates, we show that for the impulsive phase as a whole the total momentum of upflowing soft X-ray plasma equaled that of the downflowing Hα plasma, to within an order of magnitude, in all four events. Only the chromospheric evaporation model predicts equal total momentum in the upflowing soft X-ray-emitting and downflowing Hα-emitting material.