34th Solar Physics Division Meeting, June 2003
Session 23 Coronal Mass Ejections II
Oral, Thursday, June 19, 2003, 11:00am-12:00noon, Auditorium

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[23.01] Evidence for Gradual External Reconnection Leading to Explosive Eruption of a Solar Filament


We observe a slowly-evolving quiet region solar eruption of 1999 April~18, using images in 195~Å\ Fe~{\sc xii} from EIT on SOHO, and in soft X-rays from SXT on Yohkoh. We examine dimmings and brightenings in difference images, where an early image is subtracted from later images, for evidence of the eruption mechanism. A filament rose slowly at about 1~km~s-1 for six hours before being rapidly ejected at about 10~km~s-1, leaving flare brightenings and post-flare loops in its wake. SOHO MDI data show that the eruption occurred in a quadrupolar region, with the filament location splitting the four magnetic sources. During the slow rise, subtle EIT dimmings occur between the filament and one of the remote magnetic regions. Concurrently, soft X-ray brightenings occur between the filament and either remote magnetic region. Both of these effects suggest temperature enhancements in magnetic loop systems on either side of the filament prior to eruption. Pre-eruption SXT dimmings occur on either side of and very close to the slowly rising filament, indicating expansion of enveloping magnetic loops. At the start of the rapid ejection, intense dimmings occur at the locations evacuated by the filament, and brightenings occur underneath the fast-moving but still low-altitude filament. We consider two models for explaining the eruption: ``breakout,'' which says that reconnection occurs high above the filament prior to eruption, and ``tether cutting,'' which says that the eruption is driven by reconnecting field lines beneath the filament. We find that pre-eruption evolution is consistent with breakout. Tether cutting-type reconnection occurs during the rapid ejection, but our data are not complete enough to determine whether that reconnection is the primary cause of the fast-phase onset.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.