Double-diffusive instabilities of a shear-generated magnetic layer

TL;DR

This paper numerically confirms that double-diffusive magnetic buoyancy instabilities can occur in shear-generated magnetic layers under certain conditions, potentially explaining magnetic phenomena in the solar tachocline.

Contribution

It demonstrates the existence of double-diffusive magnetic buoyancy instabilities in high Richardson number shear flows through numerical simulations.

Findings

Instabilities occur when magnetic to thermal diffusivity ratio is low.

Such instabilities are possible even in high shear environments.

Relevance to solar tachocline magnetic dynamics.

Abstract

Previous theoretical work has speculated about the existence of double-diffusive magnetic buoyancy instabilities of a dynamically evolving horizontal magnetic layer generated by the interaction of forced vertically sheared velocity and a background vertical magnetic field. Here we confirm numerically that if the ratio of the magnetic to thermal diffusivities is sufficiently low then such instabilities can indeed exist, even for high Richardson number shear flows. Magnetic buoyancy may therefore occur via this mechanism for parameters that are likely to be relevant to the solar tachocline, where regular magnetic buoyancy instabilities are unlikely.