Formation of a Solar Filament Channel

Abstract

We present observations of the early stages of formation of a Ðlament channel when a compact activity complex emerged in a previously quiet, near-equatorial area. In a few hours, and while Ñux was rising rapidly in one bipolar component in the complex, Ha Ðne structure overlying a polarity inversion zone organized into a conspicuous pattern of parallel Ðbrils enclosing the trailing end of the new activity complex. Yet it took another 4 days for a stable Ðlament to form inside that pattern. It did so at a place where migrating positive polarity Ñux from the new activity complex contacted the negative polarity Ñux in a plage of an adjacent decaying bipolar active region. In contrast, no Ðlament formed along an existing channel inside the adjacent decaying region ; the opposite-polarity Ñuxes on the borders of the existing channel showed no signs of convergence. We attribute the Ðbril-aligning forces in the new channel to the horizontal component of an extended nonpotential magnetic Ðeld caused by currents in the multi-polar activity complex. The channel is, in this view, an elementary part of the magnetic topology of an activity complex. We propose that the later formation of the Ðlament in the new channel requires an additional and separate process. A plausible candidate for this second step is the development of a current sheet at the site of converging magnetic Ñux.