Small Magnetic Bipoles Emerging in a Filament Channel

Abstract

Observations have shown that quiescent prominences or filaments have a hemispheric magnetic pattern of chirality. Motivated by the question of whether the filament chirality is of subsurface origin or not, we have studied small magnetic bipoles that emerged in a quiescent filament channel at latitude N45°. During our 5 day observing run, performed in 1999 October, a huge filament erupted and reformed shortly in the same filament channel. Using high-cadence, long-integration line-of-sight magnetograms taken at Big Bear Solar Observatory, we identified a total of 102 bipoles that showed an average total flux of 2.8 × 1019 Mx, an average separation of 7400 km at the time of full development, and an emergence rate of 430 hr-1 per the entire solar surface area. These properties indicate that most of the bipoles are ephemeral regions. The most important finding in the present study is that the magnetic axes of the bipoles emerging in the filament channel are systematically oriented; a negative (trailing) pole is observed to be located preferentially to the south-east of its companion positive (leading) pole. This preferred orientation does not match either the Hale law of active region orientation or a theory that attributes the axial field of a filament to emerging bipoles. We propose two possible subsurface field configurations of bipoles consistent with the observed preferential orientation and discuss physical implications of our results for understanding filament magnetic fields.