Turbulent diffusion with rotation or magnetic fields

TL;DR

This paper investigates how rotation and magnetic fields influence turbulent diffusion, revealing anisotropic effects and suppression of transport, with implications for solar convective energy transfer.

Contribution

It provides a detailed analysis of the anisotropic turbulent diffusion tensor under rotation and magnetic fields, highlighting differences in transport suppression.

Findings

Rotation causes sideways deflection of mean concentration flux.

Magnetic fields suppress turbulent transport less along their direction.

Transport along the rotation axis is weakly affected except at small scales.

Abstract

The turbulent diffusion tensor describing the evolution of the mean concentration of a passive scalar is investigated for non-helically forced turbulence in the presence of rotation or a magnetic field. With rotation, the Coriolis force causes a sideways deflection of the flux of mean concentration. Within the magnetohydrodynamics approximation there is no analogous effect from the magnetic field because the effects on the flow do not depend on the sign of the field. rotation and magnetic fields tend to suppress turbulent transport, but this suppression is weaker in the direction along the magnetic field. Turbulent transport along the rotation axis is not strongly affected by rotation, except on shorter length scales, i.e., when the scale of the variation of the mean field becomes comparable with the scale of the energy-carrying eddies. These results are discussed in the context of anisotropic convective energy transport in the Sun.