  We present direct numerical simulations of the equations of compressible
magnetohydrodynamics in a wedge-shaped spherical shell, without shear, but with
random helical forcing which has negative (positive) helicity in the northern
(southern) hemisphere. We find a large-scale magnetic 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 time scales with reversals of polarity and equatorward
migration. Corresponding mean-field models also show similar migratory
oscillations with a frequency that is nearly independent of the magnetic
Reynolds number. This mechanism may be relevant for understanding equatorward
migration seen in the solar dynamo.
