Strong field dynamo action in rapidly rotating convection with no inertia

TL;DR

This paper demonstrates that in rapidly rotating convection models neglecting inertia, a new branch of dynamo solutions can generate strong magnetic fields, aligning with the Earth's core force balance.

Contribution

It introduces a model neglecting inertia to achieve a dynamo solution with realistic force balance, revealing a new branch of strong magnetic field solutions.

Findings

Strong magnetic fields are generated in the inertia-less rotating convection model.

The solutions differ significantly from weak-field cases, showing different flow dynamics.

The model aligns with the expected geodynamo force balance.

Abstract

The Earth's magnetic field is generated by dynamo action driven by convection in the outer core. For numerical reasons, inertial and viscous forces play an important role in geodynamo models; however, the primary dynamical balance in the Earth's core is believed to be between buoyancy, Coriolis and magnetic forces. The hope has been that by setting the Ekman number to be as small as computationally feasible, an asymptotic regime would be reached in which the correct force balance is achieved. However, recent analyses of geodynamo models suggest that the desired balance has still not yet been attained. Here we adopt a complementary approach consisting of a model of rapidly rotating convection in which inertial forces are neglected from the outset. Within this framework we are able to construct a new branch of solutions in which the dynamo generates a strong magnetic field that satisfies the expected force balance. The resulting strongly magnetized convection is dramatically different to the corresponding solutions in which the field is weak.