The effect of magnetic field on mean flow generation by rotating two-dimensional convection

TL;DR

This study explores how an imposed magnetic field influences large-scale flows generated by rotating convection in a 2D model, revealing suppression, organization, and persistence of flows depending on magnetic strength and Prandtl numbers.

Contribution

It provides new insights into the magnetic field's dual role in suppressing and organizing mean flows in rotating convection, especially at different Prandtl numbers.

Findings

Increasing magnetic field strength generally suppresses mean flows.

Magnetic fields can organize flows, leading to stronger time-averaged flows.

Significant mean flows can persist at low Prandtl numbers despite magnetic suppression.

Abstract

Motivated by the significant interaction of convection, rotation and magnetic field in many astrophysical objects, we investigate the interplay between large-scale flows driven by rotating convection and an imposed magnetic field. We utilise a simple model in two dimensions comprised of a plane layer that is rotating about an axis inclined to gravity. It is known that this setup can result in strong mean flows; we numerically examine the effect of an imposed horizontal magnetic field on such flows. We show that increasing the field strength in general suppresses the time-dependent mean flows, but in some cases it organises them leading to stronger time-averaged flows. Further, we discuss the effect of the field on the correlations responsible for driving the flows and the competition between Reynolds and Maxwell stresses. A change in behaviour is observed when the (fluid and magnetic) Prandtl numbers are decreased. In the smaller Prandtl number regime, it is shown that significant mean flows can persist even when the quenching of the overall flow velocity by the field is relatively strong.