Precession-driven dynamos in a full sphere and the role of large scale cyclonic vortices

TL;DR

This paper investigates how precession-driven flows in a full sphere can generate magnetic fields, emphasizing the role of large scale cyclonic vortices, with implications for planetary dynamo models.

Contribution

It demonstrates the occurrence of precession-driven dynamos across various flow regimes, highlighting the novel role of large scale cyclonic vortices in magnetic field generation.

Findings

Dynamos are sustained from laminar to turbulent flows.

Large scale cyclonic vortices significantly contribute to magnetic field generation.

Dynamo action occurs at low Ekman and magnetic Prandtl numbers.

Abstract

Precession has been proposed as an alternative power source for planetary dynamos. Previous hydrodynamic simulations suggested that precession can generate very complex flows in planetary liquid cores [Y. Lin, P. Marti, and J. Noir, "Shear-driven parametric instability in a precessing sphere," Physics of Fluids 27, 046601 (2015)]. In the present study, we numerically investigate the magnetohydrodynamics of a precessing sphere. We demonstrate precession driven dynamos in different flow regimes, from laminar to turbulent flows. In particular, we highlight the magnetic field generation by large scale cyclonic vortices, which has not been explored previously. In this regime, dynamos can be sustained at relatively low Ekman numbers and magnetic Prandtl numbers, which paves the way for planetary applications.