Turbulent 3D MHD dynamo model in spherical shells: Regular oscillations of the dipolar field

TL;DR

This paper presents 3D numerical simulations of convection-driven dynamos in spherical shells, showing how boundary conditions induce a transition from steady to oscillating dipolar magnetic fields.

Contribution

It demonstrates that stress-free boundary conditions primarily cause the transition to regular oscillations in the dipolar magnetic field.

Findings

Transition from non-oscillatory to oscillatory dipolar fields due to boundary conditions

Weaker magnetic fields are associated with oscillations

Inner to outer radius ratio has minimal effect

Abstract

We report the results of three-dimensional numerical simulations of convection-driven dynamos in relatively thin rotating spherical shells that show a transition from an strong non-oscillatory dipolar magnetic field to a weaker regularly oscillating dipolar field. The transition is induced primarily by the effects a stress-free boundary condition. The variation of the inner to outer radius ratio is found to have a less important effect.