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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg
Our analysis of active region AR7220/7222 has revealed some remarkable features of the solar coronal magnetic field: The region of bright X-ray loops is bounded by separatrix surfaces and restricted to regions of short field lines. Surrounding areas conspicuously lacking in soft X-ray emission are connected by long field lines to distant opposite polarity. The force-free field lines align well with observed coronal loops and agree better than potential field lines do. The footpoints of the brightest set of loops lie in a photospheric flux tube which has a very distinct sheath of return current. Furthermore, the bright loops appear to have both ends rooted in quite strong magnetic field (\approx 500 G). The separatrix surfaces do not seem to contribute to heating of the loops; the lengths of the field lines and field strength at the footpoints seem to be the most significant factors. These findings stimulate us to investigate the physics of loop heating in other active regions. We reconstruct the coronal magnetic field of AR6919 from a series of three magnetograms which span the 1991 November 15 flare event. We also compare coronal fields of AR6919 computed from two kinds of boundary conditions: one with \alpha specified everywhere, the other with \alpha specified only over one polarity. We expand our study of loop heating by computing loop brightnesses based on heating fluxes dependent on the footpoint magnetic field strength, apply the coronal loop scaling law to determine temperature and density, and map these onto the computed field lines. We compute the X-ray flux and integrate along the line-of-sight to obtain two-dimensional images.
Program listing for Friday