The eruptive flare of 15 November 1991: Preflare phenomena

We present and interpret observations of the preflare phase of the eruptive flare of 15 November, 1991 in NOAA AR 6919. New flux emerged in this region, indicated by arch filaments in Ha and increasing vertical flux in vector magnetograms. With increasing frequency before the eruption, transient dark H alpha fibrils were observed that crossed Ha bright plage and the magnetic inversion line to extend from the region of flux emergence to the filament, whose eruption was associated with the flare. These crossing fibrils were dynamic, and were often associated with sites of propagating torsional motion. These sites propagated from the region of flux emergence into the filament Aux system. We interpret these morphological and dynamic features in terms of relaxation after magnetic reconnection episodes which create longer held lines within the filament Aux system, as envisioned in the tether cutting model, and transfer twist to it, as well.