AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 31. Magnetic Reconnection and Prominence Formation
Oral, Monday, May 31, 1999, 2:00-3:30pm, Continental Ballroom A

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[31.07] Quadrupolar Magnetic Reconnection in Solar Flares

M.J. Aschwanden (Lockheed-Martin Solar and Astrophysics Lab.), T. Kosugi (Inst. of Space and Astronautical Science, Japan), Y. Hanaoka (Nobeyama Radio Obs., Japan), M. Nishio (Dept. of Physics, Kagoshima University, Japan), D.B. Melrose (School of Physics, U. Sydney, Australia)

We analyze the 3-dimensional (3D) geometry of solar flares that show so-called interacting flare loops in soft X-ray, hard X-ray, and radio emission, as previously identified by Hanaoka and Nishio. The two flare loops that appear brightest after the flare are assumed to represent the outcome of a quadrupolar magnetic reconnection process, during which the connectivity of magnetic polarities is exchanged between the four loop footpoints. We fit a 10-parameter 3D-model to Yohkoh SXT and HXT data of 10 solar flares and determine this way the pre-reconnection and post-flare geometry of interacting flare loops. We apply a flare model of Melrose to calculate the magnetic flux transfer and energy released when two current-carrying field lines reconnect to form a new current-carrying system in a quadrupolar geometry. Some findings are: (1) The pre-reconnection field lines always show a strong asymmetry in size, consistent with the scenario of new-emerging small-scale loops that reconnect with pre-existing large-scale loops. (2) The relative angle between reconnecting field lines is near-collinear in half of the cases, and near-perpendicular in the other half, contrary to the anti-parallel configuration suggested in the model of Heyvaerts et al. (3) The shear angle between interacting field lines reduces by 10-50 deg after quadrupolar reconnection. (4) The small-scale flare loop experiences a shrinkage by a factor of 1.31+0.44, which is consistent with the scaling law found from previous electron time-of-flight measurements, suggesting that electron acceleration occurs near the cusp of quadrupolar configurations. (5) The large-scale loop is found to dominate the total induction between current-carrying loops, providing a simple estimate of the maximum magnetic energy available for flare energy release due to current transfer, which scales as E=10(29.63) [r2/10(9) cm] [I2/10(11) A]2, (with r2 the curvature radius and I2 the current of the large-scale loop) and is found to correlate with observed flare energies deduced from soft X-ray and hard X-ray fluxes. Most of the energy is transferred to small-scale loops that have half of the large-scale current I1=I2/2. (6) The quadrupolar reconnection geometry provides also a solution of ``Canfield's dilemma" of the offset between the maximum of vertical currents and the HXR flare loop footpoints.

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