Filament Eruptions and the Impulsive Phase of Solar Flares
Rept. for 18 May 1987-17 May 1988
EMERSON RADIO AND PHONOGRAPH CORP JERSEY CITY NJ
Pagination or Media Count:
We examine the observed development of filament eruptions in the impulsive phase of flares for evidence of how the eruption is driven. A possibility sometimes adopted as working hypothesis is that the filament eruption and accompanying coronal mass ejection are consequences of energy release in the flare impulsive phase they are taken to be ejecta in the explosion resulting from the pressure pulse from plasma heating in the flare. Evidence against this view is from four flares in which, in H alpha movies, a filament eruption was observed during the flare impulsive phase defined by the E approx. 30 keV hard X-ray emission observed with the U. of Calif. at Berkely detector on the ISEE 3 spacecraft. In each case we find that 1 filament eruption began before onset of the impulsive phase 2 eruptive motion is consistent with a smooth evolution through the impulsive phase, accelerating, but showing no new acceleration attributable to the impulsive phase 3 brightening of the H alpha flare ribbons in the impulsive phase occurring in compact areas is much smaller than the overall span of the erupting filament and 4 the observed projected speed is on the order of 100 kms at the onset of the impulsive phase. These characteristics indicate that filament eruption is not driven by flare plasma pressure, but instead marks an eruption of magnetic field driven by a global MHD instability of the field configuration in the flare region. It appears that filament eruption and impulsive energy release are coordinated and driven by a common cause, the instability of the whole field configuration. A new mode of energy release, that of the impulsive phase, may be initiated when the eruptive motion surpasses some speed limit of order 100 kms.