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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.
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