**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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## [55.02] Cylindrical Compressible Magnetoconvection and Model Sunspots

*N. Hurlburt, D Alexander (Lockheed Martin Solar and Astrophysics Laboratory), A. Rucklidge (Cambridge University)*

We present results of hybrid models of sunspots and pores
which encompasses both the nonlinear, compressible
magnetoconvection beneath the photosphere, potential models
of the coronal fields and includes quasistatic coronal
heating models.

We solve the equations that describe compressible
magnetoconvection in 2D axisymmetric and 3D cylindrical
geometries using compact finite difference scheme. The
convecting layer consists of electrically conducting gas
which experiences a uniform gravitational acceleration
directed downwards. The gas possesses a shear viscosity, a
thermal conductivity, a magnetic diffusivity, and a magnetic
permeability which are all assumed to be constant. We assume
that the fluid satisfies the equation of state for a perfect
monatomic gas with constant heat capacities. At the bottom
of the cylinder, we impose a constant temperature and
vertical magnetic field. On the top surface apply instead a
radiative, and linear force-free field condition. The outer
boundary is insolating and perfectly conducting.

The magnetic fields above the computational domain are then
extrapolated and heated using a quasistatic model. The
heating problem is solved in an empirical way by assuming
that individual fluxtubes are heated in a manner that is
proportional to one or more of the parameters defining the
fluxtube, e.g. pressure, length, field strength, current
density etc. The combination of a sunspot model, whereby the
surface field is completely specified, with a coronal
heating model, in which the plasma parameters are specified
for a given energy input allows us to explore a broad class
of heating paradigms.

We present result of 2D simulations with no net magnetic
flux which display phenomena similar to that observed in
sunspot moats, and 3D simulations which develop
penumbral-like structure. This work was supported by NASA
contract NAG5-7376.

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

http://www.lmsal.com

hurlburt@lmsal.com

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