34th Solar Physics Division Meeting, June 2003
Session 16 Flares and Microflares II
Poster, Wednesday, June 18, 2003, 3:30-5:00pm, Mezzanine

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[16.14] Time Profiles of Magnetic Reconnection Measured from Flare Ribbons

T. Tarbell (LMSAL), T. Gaeng (L-3 Com EER Systems at GSFC), J. Saba (LMSAL at GSFC)

We study flare ribbons using observations of very high temporal and spatial resolution to measure time profiles of magnetic reconnection. TRACE images in the 1600 band show flare ribbons in the low chromosphere, and we analyze M and X-class events with time resolution as high as a few seconds during the buildup, impulsive and decay phases. MDI high resolution magnetograms provide photospheric fields for estimation of reconnection rates in Mx/s. Another M-class event is studied with La Palma observations of very high spatial resolution but lower cadence; H-alpha images are used to locate the flare ribbons in this case. Both types of data show examples in weak plage or network where the flare ribbons do not overlie significant photospheric magnetic fields. We believe these ribbons are in the chromospheric magnetic canopy, where fields are nearly horizontal and flare heating can be widely separated from the photospheric footpoints. In regions of stronger fields, we argue that careful spatial coalignment of flare ribbons with photospheric fields can provide information about the time profile of reconnection in the corona. The reconnection rate is very noisy, with a correlation time of at most a few seconds. During the gradual buildup to one of the M flares, an exponential growth in reconnection rate by two orders of magnitude over 40 minutes before the impulsive phase is observed. Rates during the gradual decay of a long duration event are also measured.

This work was supported by NASA contracts NAG5-10483 (MDI) and NAS5-38099 (TRACE).


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