Mon. Not. R.
Astron. Soc. 301, 593-608 (1998).
Modelling photospheric magnetoconvection
A.M. Rucklidge and
Department of Applied Mathematics and Theoretical Physics,
University of Cambridge, Cambridge, CB3 9EW, UK
The increasing power of computers makes it possible to model the nonlinear
interaction between magnetic fields and convection at the surfaces of
solar-type stars in ever greater detail. We present the results of
idealized numerical experiments on two-dimensional
magnetoconvection in a fully compressible perfect gas. We first vary
the aspect ratio lambda of the computational
box and show that the system runs through a sequence of convective patterns,
and that it is only for a sufficiently wide box (lambda>=6) that
the flow becomes insensitive to further increases in lambda. Next,
setting lambda=6, we decrease the field strength from a value
strong enough to halt convection and find transitions to small-scale
steady convection, next to spatially modulated oscillations (first
periodic, then chaotic) and then to a new regime of flux separation,
with regions of strong field (where convection is almost completely
suppressed) separated by broad convective plumes. We also explore the
effects of altering the boundary conditions and show that this
sequence of transitions is robust. Finally, we relate these model
calculations to recent high-resolution observations of solar
magnetoconvection, in plage regions as well as in light bridges and the
umbrae of sunspots.
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