Oscillatory migrating magnetic fields in helical turbulence in spherical domains

Abstract

We present direct numerical simulations of the equations of compressible magnetohydrodynamics in a wedgeshaped spherical shell, without shear, but with random helical forcing which has negative (positive) helicity in the northern (southern) hemisphere.We find a large-scalemagnetic field that is nearly uniform in the azimuthal direction and approximately antisymmetric about the equator. Furthermore, the large-scale field in each hemisphere oscillates on nearly dynamical timescales with reversals of polarity and equatorward migration. Corresponding mean-field models also showsimilarmigratory oscillations with a frequency that is nearly independent of themagnetic Reynolds number. This mechanism may be relevant for understanding equatorward migration seen in the solar dynamo. © 2010. The American Astronomical Society. All rights reserved.