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Session 17 - Magnetic Fields II.
Oral session, Tuesday, July 01
Ballroom A, Chair: Paul Charbonneau

[17.06] A Conceptual Model of the Formation of Filament Barbs

S. F. Martin (Helio Research)

Barbs are the structures along the sides of a filament that connect its horizontal axis to chromosphere. The barbs, previously called 'legs' can be considered as magnetic field conduits along which mass is continuously guided and transported to and from the chromosphere. In the model presented, the barbs represent a secondary stage in filament formation which follows an intial stage in which a nearly horizontal axial magnetic field is first formed along a filament channel. Barb formation is most effectively and readily illustrated where the filament channel is broad and well-developed such as exists among the decaying network remnants of active regions. In these circumstances, the filament channel is a region of relatively low magnetic flux density compared to adjacent areas further from the polarity inversion. H-alpha filtergrams show that the axial parts of the filament are low and nearly contiguous with the chromosphere. The low height of the axial field, and the relative absence of concentrations of network magnetic field, are favorable conditions for magnetic reconnection between the axial field of the filament and new ephemeral regions and intranetwork magnetic fields beneath the filament. These reconnections lead to the formation of the barbs joining parts of the newly emerged fields to the axial field of the filament. Barb formation and motions seen in H-alpha filtergrams provide the evidence for this initial part of the conceptual model. The remaining part of the model is a demonstration of why only right-bearing barbs are seen on dextral filaments and left-bearing barbs on sinistral filaments; this is due to the sinistral or dextral magnetic configuration of the filament channel which does not permit the survival of barbs of the non-observed chirality as will be illustrated.

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