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Session 86 - Coronal Activity.
Oral session, Thursday, June 13
Previous simulations of magnetic reconnection in both symmetric and asymmetric topologies (Karpen, Antiochos, amp; DeVore 1995, ApJ, 450, 422; ApJL, 460, L73) demonstrated that shear-driven reconnection can reproduce several fundamental features of chromospheric eruptions (e.g., spicules, surges, and the HRTS explosive events). In asymmetric systems, moreover, the random nature of the reconnection yields numerous current sheets over a large but well-defined volume resembling a coronal loop in profile, a phenomemon which we denoted Reconnection Driven Current Filamentation. However, in these calculations the field was subjected to footpoint shearing much stronger than typical photospheric motions. In this talk we will discuss the response of the symmetric topology to footpoint motions approximately an order of magnitude slower, commensurate with typical photospheric flow speeds. The finite-difference simulation was performed with a new, parallelized version of our 2.5-dimensional FCT-based code (MAG25D), which solves the ideal compressible MHD equations with complex boundary conditions; numerical diffusivity alone provided localized reconnection. We find that reconnection proceeds in an uneven manner, as the field around the initial X point oscillates aperiodically between vertical and horizontal current sheet formations, while the larger-scale surrounding field rises and falls. The greater separation between the driver and the characteristic plasma (e.g., the Alfvén transit) time scales reveals a variety of behaviors ranging from rapid bursts of reconnection to the slow ``breathing" of the large-scale stressed field. In addition, we will explore the implications of these results for the applicability of fast (Petschek) reconnection models to the solar atmosphere.
Program listing for Thursday