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R. Cameron (Caltech)
The magnetic flux threading the solar surface is believed to be concentrated by convective motions into kilogauss strength flux tubes. What is less well known is the extent to which convective motions also concentrates the vertical current threading the solar surface. This question can be addressed using the non-ideal MHD approximation. As is the case with most such nonlinear problems a numerical treatment is called for. This issue is perhaps best treated in an axisymmetric geometry, where the computational cost of the calculations remains modest (2 1/2 dimensional) compared with a full 3 dimensional simulation, and where flux tubes rather than flux sheets (which form in 2 1/2 dimensional planar simulations) are produced. The problem then equates to that of twisted, axisymmetric magnetoconvection, which has been treated in the Boussinesq problem by Jones and Galloway (1993). The results obtained in the Boussinesq problem indicate that the problem is sensitive to the way in which the azimuthal components are generated by the boundary conditions. This paper extends that work by including the effect of compressibility. Compressible axisymmetric magnetoconvection has two non-dimensional parameters in addition to those describing the Boussinesq problem. To isolate the effect of compressibility, we treat the same cases as Jones and Galloway, and vary the two additional parameters.
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