Small-Scale Dynamo in Stably Stratified Turbulence

TL;DR

This paper investigates the conditions under which small-scale dynamos operate in stably stratified turbulence, focusing on the onset, growth, and magnetic field anisotropy, with implications for stellar radiative zones like the solar tachocline.

Contribution

It introduces new criteria for small-scale dynamo onset in stratified turbulence, linking dynamo properties to the scale separation between the Ozmidov and viscous or resistive scales.

Findings

Dynamo properties are controlled by scale separation between Ozmidov and viscous/resistive scales.

Defined critical buoyancy and magnetic buoyancy Reynolds numbers for dynamo onset.

Stratification in the solar tachocline is marginally sufficient for dynamo activity.

Abstract

We present numerical investigations into three principal properties of the small-scale dynamo in stably stratified turbulence: the onset criterion, the growth rate, and the nature of the magnetic field anisotropy in the kinematic regime. The results suggest that all three dynamo properties are controlled by the scale separation between the Ozmidov scale and the viscous or resistive scale. In addition to the critical magnetic Reynolds number, this allows for the definition of critical buoyancy and magnetic buoyancy Reynolds numbers for stratified small-scale dynamo onset in the high and low magnetic Prandtl number regimes, respectively. The presence of a small-scale dynamo in stellar radiative zones could affect dynamics through resulting Maxwell stresses and/or influence large-scale dynamo mechanisms in regions of differential rotation. Taking the solar radiative zone as a representative example and applying the onset criterion, we find that the stratification is strong enough to make the small-scale dynamo marginally active in the stably stratified turbulence of the solar tachocline.