The Effect of Velocity Shear on Dynamo Action Due to Rotating Convection

TL;DR

This paper investigates how large-scale horizontal velocity shear influences dynamo action in rotating convection, revealing that shear enhances magnetic field generation and alters the structure of the resulting magnetic fields.

Contribution

It introduces the analysis of shear flow effects on dynamo processes in rotating convection, highlighting the importance of scale interactions and spectral filtering techniques.

Findings

Shear flow increases dynamo growth rates.

Large-scale magnetic fields are generated with shear.

Different flow scales produce distinct magnetic structures.

Abstract

Recent numerical simulations of dynamo action resulting from rotating convection have revealed some serious problems in applying the standard picture of mean field electrodynamics at high values of the magnetic Reynolds number, and have thereby underlined the difficulties in large-scale magnetic field generation in this regime. Here we consider kinematic dynamo processes in a rotating convective layer of Boussinesq fluid with the additional influence of a large-scale horizontal velocity shear. Incorporating the shear flow enhances the dynamo growth rate and also leads to the generation of significant magnetic fields on large scales. By the technique of spectral filtering, we analyse the modes in the velocity that are principally responsible for dynamo action, and show that the magnetic field resulting from the full flow relies crucially on a range of scales in the velocity field. Filtering the flow to provide a true separation of scales between the shear and the convective flow also leads to dynamo action; however, the magnetic field in this case has a very different structure from that generated by the full velocity field. We also show that the nature of the dynamo action is broadly similar irrespective of whether the flow in the absence of shear can support dynamo action.