Turbulent transport and dynamo in sheared MHD turbulence with a non-uniform magnetic field

TL;DR

This paper studies how large-scale velocity and magnetic field shears influence turbulence and magnetic dynamo processes in three-dimensional magnetohydrodynamics, revealing complex interactions that affect turbulence intensity and transport.

Contribution

It provides a detailed analysis of the combined effects of flow and magnetic shear on turbulence and turbulent transport in MHD, including quenching and enhancement mechanisms.

Findings

Turbulence viscosity and diffusivity are quenched by strong shear and magnetic fields.

Magnetic shear can increase turbulence intensity while decreasing turbulent transport.

Strong flow shear and magnetic shear can oppose each other's effects on turbulence.

Abstract

We investigate three-dimensional magnetohydrodynamics turbulence in the presence of both a large-scale velocity and non-uniform magnetic field. By assuming a turbulence driven by an external forcing with both helical and non-helical spectra, we investigate the combined effect of these two shears on turbulence intensity and turbulent transport represented by turbulent diffusivities (turbulent viscosity, $\alpha$ and $\beta$ effect) in analogy with Reynolds. We show that turbulence viscosity and diffusivity are quenched for strong flow shear and magnetic field in the limits of weak and strong magnetic field, respectively. For a weak flow shear, we further show that the magnetic shear increases the turbulence intensity while decreasing the turbulent transport. In the presence of a strong flow shear, the effect of the magnetic shear is found to oppose the effect of flow shear (which reduces turbulence due to shear stabilization) by enhancing turbulence and transport, thereby weakening the strong quenching by flow shear stabilization. In the case of a strong magnetic field (compared to flow shear), magnetic shear increases turbulence intensity and quenches turbulent transport.