**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.

If the author provided an email address or URL for general inquiries,
it is as follows:

manchest@ncar.ucar.edu

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