Magnetic structure, dipole reversals, and 1/f noise in resistive MHD spherical dynamos

TL;DR

This study investigates magnetic dipole reversals and 1/f noise in resistive MHD spherical dynamos through numerical simulations, revealing geodynamo-like behavior, long-term memory effects, and frequency spectra trends related to control parameters.

Contribution

It provides new insights into the conditions leading to dipole reversals and 1/f noise in resistive MHD spherical dynamos, highlighting the influence of Ekman and Reynolds numbers.

Findings

Dipole reversals occur at low Ekman and high Reynolds numbers.

Waiting times between reversals follow a non-Poissonian distribution.

A 1/f frequency power spectrum is observed in the magnetic dipole time-series.

Abstract

A parametric study of the magnetic dipole behavior in resistive incompressible MHD inside a rotating sphere is performed, using direct numerical simulations and considering Reynolds and Ekman numbers as controlling parameters. The tendency is to obtain geodynamo-like magnetic dipole reversal regimes for sufficiently small Ekman and large Reynolds numbers. The typical dipole latitude obtained in the reversal regime is around 40 degrees (with respect to the rotation axis of the sphere). A statistical analysis of waiting times between dipole reversals is also performed, obtaining a non-Poissonian distribution of waiting times, indicating long-term memory effects. We also report the presence of a $1/f$ frequency power spectrum in the magnetic dipole time-series, which also shows a tendency to grow toward lower frequencies as the Ekman number is decreased.