Behavior of hydrodynamic and magnetohydrodynamic turbulence in a rotating sphere with precession and dynamo action

TL;DR

This study investigates how precession influences turbulence and magnetic field generation in a rotating sphere, revealing conditions for dynamo action and magnetic reversals through numerical simulations.

Contribution

It provides new insights into the effects of precession on hydrodynamic and magnetohydrodynamic turbulence and dynamo behavior in rotating spheres.

Findings

No self-sustaining dynamos in prograde precession

Critical retrograde precession frequency for dynamo onset

Magnetic dipole reversals with frequency-dependent waiting times

Abstract

The effect of precession in a rotating sphere filled with fluid was studied with direct numerical simulations, both in the incompressible hydrodynamics (HD) and magnetohydrodynamics (MHD) scenarios. In both cases the asymptotic state and its dependence with both rotating and precession frequency was analyzed. For the MHD case no self-sustaining dynamos were found for the prograde precession case, whereas on the other hand a critical retrograde precession frequency was found above which dynamo action is self-sustained. It was also found that these correspond to small-scale dynamos with a developed turbulent regime. Furthermore, it is observed the presence of reversals of the magnetic dipole moment with greater waiting times between reversals for smaller precession frequencies.