Oscillatory migrating magnetic fields in helical turbulence in spherical domains

TL;DR

This study uses numerical simulations to explore magnetic field oscillations and migrations in a spherical domain with helical turbulence, providing insights into solar dynamo phenomena.

Contribution

It demonstrates that large-scale magnetic fields in spherical helical turbulence can oscillate and migrate, aligning with solar magnetic behavior, using direct numerical simulations and mean-field models.

Findings

Large-scale magnetic fields are nearly uniform azimuthally and antisymmetric about the equator.

Fields oscillate with polarity reversals and migrate toward the equator.

Oscillation frequency is nearly independent of magnetic Reynolds number.

Abstract

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.