Bistability between equatorial and axial dipoles during magnetic field reversals

TL;DR

This paper investigates how breaking equatorial symmetry in geodynamo simulations leads to bistability and reversals between axial and equatorial magnetic dipoles, offering new insights into Earth's magnetic field behavior.

Contribution

It demonstrates the existence of bistability and polarity reversals between dipole configurations in geodynamo models with symmetry breaking, a novel scenario for magnetic field reversals.

Findings

Bistability between axial and equatorial dipoles observed.

Chaotic polarity switches involve the equatorial dipole.

Symmetry breaking influences magnetic field structure and reversals.

Abstract

Numerical simulations of the geodynamo in presence of an heterogeneous heating are presented. We study the dynamics and the structure of the magnetic field when the equatorial symmetry of the flow is broken. If the symmetry breaking is sufficiently strong, the m = 0 axial dipolar field is replaced by an hemispherical magnetic field, dominated by an oscillating m = 1 magnetic field. Moreover, for moderate symmetry breaking, a bistability between the axial and the equatorial dipole is observed. In this bistable regime, the axial magnetic field exhibits chaotic switches of its polarity, involving the equatorial dipole during the transition period. This new scenario for magnetic field reversals is discussed within the framework of the Earth's dynamo.