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V. B. Yurchyshyn, H. Wang, J. Qiu, P.R. Goode (Big Bear Solar Observatory), V.I. Abramenko (Crimean Astrophysical Observatory)
We analyzed the 3D structure of the linear force-free magnetic field in an active region. A longitudinal magnetogram of AR NOAA 8375 has been used as the photospheric boundary condition. The Nov 5, 1998 2B/M8.4 two-ribbon flare can be explained in the framework of quadrupolar reconnection theory: the interaction of two closed magnetic loops which have a small spatial angle. The energy derived from SXT/YOHKOH data (3 - 6 \times 1030 ergs) is one order of magnitude higher than the lower limit of flare energy predicted by Melrose's model. The latter estimation was made using the linear force-free extrapolation. It is suggested that by taking into account the non-linear character of the observed magnetic field we can increase the lower limit of the magnetic energy stored in the studied magnetic configuration. The revealed magnetic configuration allows us to understand the observed location and evolution of the flare ribbons and the additional energy released during the gradual phase of the flare, as well. Also, the reconnection of closed magnetic loops can logically explain the connection between a two-ribbon flare and the giant X-ray post-flare arch which usually is observed after flare onset. We emphasize that unlike the Kopp and Pneuman configuration, the model discussed here doesn't necessarily need destabilization and opening of the magnetic field.
This work was supported in part by NSF-ATM (97-14796) and NASA (NAG5-4919) grants.
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