Generation of large-scale vorticity in rotating stratified turbulence with inhomogeneous helicity: mean-field theory

TL;DR

This paper develops a mean-field theory explaining how large-scale vorticity can be generated in rotating, stratified turbulence with inhomogeneous helicity, highlighting the roles of shear, Reynolds stress, and rotation.

Contribution

It introduces a new mean-field theoretical framework for understanding large-scale vorticity generation in complex turbulent flows with rotation and stratification.

Findings

Large-scale vorticity arises from combined effects of stratification, rotation, and inhomogeneous helicity.

Large-scale shear interacts with small-scale turbulence to excite a vorticity dynamo.

Fast rotation suppresses the large-scale vorticity instability.

Abstract

We discuss a mean-field theory of generation of large-scale vorticity in a rotating density stratified developed turbulence with inhomogeneous kinetic helicity. We show that the large-scale nonuniform flow is produced due to ether a combined action of a density stratified rotating turbulence and uniform kinetic helicity or a combined effect of a rotating incompressible turbulence and inhomogeneous kinetic helicity. These effects result in the formation of a large-scale shear, and in turn its interaction with the small-scale turbulence causes an excitation of the large-scale instability (known as a vorticity dynamo) due to a combined effect of the large-scale shear and Reynolds stress-induced generation of the mean vorticity. The latter is due to the effect of large-scale shear on the Reynolds stress. A fast rotation suppresses this large-scale instability.