THE 1991-OCTOBER-24 FLARE - A CHALLENGE FOR STANDARD MODELS

The M9.8 solar flare of 1991 October 24 22:30 UT presents several inte resting characteristics: (1) energy release starts high in the corona; (2) the primary chromospheric ribbons are initially well separated an d do not move apart at an observable rate; (3) no evidence is found fo r an erupting filament or other driver. To explain this flare, we cons ider several canonical flare models, including a filament eruption, a confined filament eruption, current interruption, and interacting loop s. We conclude that none of these scenarios unequivocally explains thi s flare. Two possibilities which cannot be ruled out are (1) the erupt ion of a filament unobservable in Ha which starts high in the corona a nd produces no ribbon motions smaller than our detection threshold and no perceptible expansion of the coronal X-ray source, and (2) energy release due to spontaneous, propagating reconnection which allows the system to essentially brighten in place.