AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 55. Active Region Formation and Evolution
Solar, Display, Tuesday, June 1, 1999, 10:00am-7:00pm, Southeast Exhibit Hall

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[55.08] Topologically Equivalent Magnetostatic Atmospheres and Numerical MHD Simulations of Buoyancy Instabilities

W. Manchester, B.C. Low (HAO/NCA and U. Illinois)

We present a physical application of two distinct families of two-dimensional analytical solutions which describe isothermal periodic magnetostatic atmospheres in uniform gravity. We demonstrate that members of both families of 2D solutions can be arrived at from the same planar atmosphere by finite plasma displacements which ensures the conservation of mass and magnetic flux. The fist family of solutions is characterized by undulating field lines which are confined to the plane of variation. By contrast, the second family of solutions has the plane of variation rotated away from the field lines. As a result, this family possesses a sheared field geometry with a field component out of the plane of variation. A striking feature of this 2D configuration is the way in which the field lines becomes highly sheared as the undulations increase in height. Both families of solutions are used as initial states for two-dimensional, time-dependent magnetohydrodynamic numerical simulations of buoyancy instabilities. The simulations demonstrate how the magnetic field component out of the plane of variation propagates into rising loops by the action of shear Alfven waves. We show that this has a profound effect on the buoyancy instability and that the resulting velocity field resembles the photospheric shear flow observed across the polarity inversion line of flux emerging regions.

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