The dynamo bifurcation in rotating spherical shells

TL;DR

This paper explores how the nature of magnetic field generation bifurcations in Earth's liquid outer core depends on key parameters, revealing complex behaviors like supercritical, subcritical, and isolated bifurcations through numerical analysis.

Contribution

It demonstrates the parameter-dependent nature of dynamo bifurcations in rotating spherical shells, highlighting the roles of magnetic Prandtl and Ekman numbers.

Findings

Bifurcation type varies with parameters.

Magnetic Prandtl and Ekman numbers influence transitions.

Complex bifurcation behaviors identified through simulations.

Abstract

We investigate the nature of the dynamo bifurcation in a configuration applicable to the Earth's liquid outer core, i.e. in a rotating spherical shell with thermally driven motions. We show that the nature of the bifurcation, which can be either supercritical or subcritical or even take the form of isola (or detached lobes) strongly depends on the parameters. This dependence is described in a range of parameters numerically accessible (which unfortunately remains remote from geophysical application), and we show how the magnetic Prandtl number and the Ekman number control these transitions.