Friday, January 11, 2013

1301.2248 (Jörn Warnecke et al.)

Solar-like differential rotation in a convective dynamo with a coronal envelope    [PDF]

Jörn Warnecke, Petri J. Käpylä, Maarit. J. Mantere, Axel Brandenburg
We report on the results of three convective dynamo simulations with an outer coronal layer. The magnetic field is self-consistently generated by the convective motions beneath the surface. Above the convection zone we include a polytropic layer that extends to 1.6 solar radii. The temperature increases in this region to $\approx8$ times the value at the surface, corresponding to $\approx1.2$ times the value at the bottom of the spherical shell. We associate this region with the solar corona. We find a solar-like differential rotation with radial contours of constant rotation rate, together with a solar-like meridional circulation and a near-surface shear layer. This spoke-like rotation profile is caused by a non-zero latitudinal entropy gradient which violates the Taylor-Proudman balance via the baroclinic term. The lower density stratification compared with the Sun leads to an equatorward return flow above the surface. The mean magnetic field is in most of the cases oscillatory with equatorward migration in one case. In other cases the equatorward migration is overlaid by stationary or even poleward migrating mean fields.
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