Monday, January 14, 2013

1301.2595 (Petri J. Käpylä et al.)

Effects of strong stratification on equatorward dynamo wave propagation    [PDF]

Petri J. Käpylä, Maarit. J. Mantere, Elizabeth Cole, Jörn Warnecke, Axel Brandenburg
We present results from simulations of rotating magnetized turbulent convection in spherical wedge geometry representing parts of the latitudinal and longitudinal extents of a star. Here we consider a set of runs for which the density stratification is varied, keeping the Reynolds and Coriolis numbers at similar values. In the case of weak stratification we find quasi-steady solutions for moderate rotation and oscillatory dynamos with poleward migration of activity belts for more rapid rotation. For stronger stratification a similar transition as a function of the Coriolis number is found, but with an equatorward migrating branch near the equator. We test the domain size dependence of our results for a rapidly rotating run with equatorward migration by varying the longitudinal extent of our wedge. The energy of the axisymmetric mean magnetic field decreases as the domain size increases and we find that an m=1 mode is excited for a full 2pi phi-extent, reminiscent of the field configurations deduced from observations of rapidly rotating late-type stars.
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