Evolution of Solar Filament Channels Observed during a Major Poleward Surge of Photospheric Magnetic Flux

Details Evolution of Solar Filament Channels Observed during a Major Poleward Surge of Photospheric Magnetic Flux Evolution of Solar Filament Channels Observed during a Major Poleward Surge of Photospheric Magnetic Flux

Sep 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...558..888g&link_type=abstract

The Astrophysical Journal, Volume 558, Issue 2, pp. 888-902.

Astronomy and Astrophysics

Astronomy

24

Sun: Activity, Sun: Filaments, Sun: Magnetic Fields, Sun: Sunspots

Scientific paper

We describe the evolution of a solar filament channel marked by extremes: a length near one solar radius, and a duration of a year. Its genesis centers on an episode of flux emergence so powerful that it launched a surge of photospheric magnetic flux almost to the northern polar cap. This extraordinary injection of new flux at the solar surface occurred in midterm of the longest lived activity complex of cycle 21 (~20 rotations). The new flux emerged just north of the equator as a pair of adjacent activity complexes-a ``supercluster'' of sunspots-remote from other active regions in a longitude band spanning ~90°. Channels quickly formed along separate polarity inversion lines in this large-scale quadrupolar configuration. None of the initial channels survived more than two solar rotations; none merged to form a greater whole. As individual bipoles within and between the activity complexes expanded, fragmented, and cancelled, only flux at the outermost edges of the adjacent complexes survived, thanks to the remoteness of other strong concentrations of magnetic flux. The result, after three solar rotations, was a simplified bipolar pattern of poleward-streaming flux subject to global processes of flux transport that sustained and extended it for up to a year. The long and long-lived filament channel formed in the shape of a ``switchback'' along the polarity inversion between the converging streams of opposite polarity flux, continuing along the polarity inversion between the migrating flux and the flux in the polar cap. Our observations reveal large-scale swirled patterns of chromospheric fibrils from which we infer that substantial negative helicity was built up across both adjacent activity complexes during their emergence. The patterns were still detectable in the migrating flux after the source regions had disappeared. Convergence of opposite polarity fluxes with negative helicity leads naturally to dextral filaments and filament channels, consistent with the chirality rule for the northern hemisphere found by Martin, Bilimoria, & Tracadas. We measured the chiralities of 10 filament channels associated with the initial massive emergence of magnetic flux and its subsequent surge poleward. Implications of our findings on models for forming filaments and filament channels are discussed.

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