Some Unusual Properties of Turbulent Convection and Dynamos in Rotating Spherical Shells

TL;DR

This paper explores the complex behaviors of turbulent convection and dynamo processes in rotating spherical shells, revealing phenomena like localized convection, oscillations, and bistable dynamo states influenced by magnetic fields.

Contribution

It uncovers unusual properties of turbulent convection and dynamos, including bistability and the impact of Lorentz forces on differential rotation in rotating spherical shells.

Findings

Differential rotation inhibits convection and causes localized phenomena.

Lorentz forces can partially or fully brake differential rotation.

Bistability exists for magnetic Prandtl numbers around unity.

Abstract

The dynamics of convecting fluids in rotating spherical shells is governed at Prandtl numbers of the order unity by the interaction between differential rotation and roll-like convection eddies. While the differential rotation is driven by the Reynolds stresses of the eddies, its shearing action inhibits convection and causes phenomena such as localized convection and turbulent relaxation oscillations. The response of the system is enriched in the case of dynamo action. Lorentz forces may brake either entirely or partially the geostrophic differential rotation and give rise to two rather different dynamo states. Bistability of turbulent dynamos exists for magnetic Prandtl numbers of the order unity. While the ratios between mean magnetic and kinetic energies differ by a factor of 5 or more for the two dynamo states, the mean convective heat transports are nearly the same. They are much larger than in the absence of a magnetic field.