A rapid change in magnetic connectivity observed before filament eruption and its associated flare

To gain insight to the cause of filament eruptions and flares on the Sun, w e observed a filament that erupted in active region NOAA 8597. The observat ions consisted of H alpha filtergrams at three wavelengths (line center and +/- 0.5 Angstrom) and line-of-sight magnetograms. All were taken on 1999 J une 24 at Big Bear Solar Observatory. We found from the time sequence of H alpha images that the filament eruption was preceded by a rapid change in c onnectivity in a bundle of filament threads. The thread bundle was initiall y sharply curved near its one end of the filament and suddenly flipped and then became straight in the new orientation. The flipped segment of the thr ead bundle swept over a 100 " x 50 " area on the solar surface in about hal f an hour. At the latter stage of the connectivity change, we observed a do wnward draining of material along the thread bundle that had a transverse c omponent of 50 km s(-1). After that, the filament body split into two paral lel parts, one part erupted while the other part remained, and the two-ribb on flare occurred. We also found canceling magnetic features in the vicinit y of the initial location of the thread end, which displayed a flux decreas e during the H alpha connectivity change. Our results show clear and direct evidence that magnetic reconnection takes place in the low atmosphere prio r to eruption. This preeruption reconnection seems to be very different fro m a posteruption coronal reconnection, which is believed to lead to a two-r ibbon flare.