Inverse cascade suppression and shear layer formation in MHD turbulence subject to a guide field and misaligned rotation

TL;DR

This study investigates how combined rotation and magnetic fields influence turbulence in astrophysical plasmas, revealing complex transitions in energy cascades and flow structures depending on the strength and alignment of these effects.

Contribution

It provides a detailed numerical analysis of the interplay between rotation and magnetic fields in MHD turbulence, highlighting the importance of limit order in strong field and rotation regimes.

Findings

Transition from inverse to forward cascade with increasing rotation

Emergence of shear-layer dominated regimes at certain parameters

Suppression of kinetic energy flux mediated by magnetic fields

Abstract

Astrophysical plasmas are often subject to both rotation and large-scale background magnetic fields. Individually, each is known to two-dimensionalize the flow in the perpendicular plane. In realistic flows, both of these effects are simultaneously present and, importantly, need not be aligned. In this work, we numerically investigate three-dimensional forced magnetohydrodynamic (MHD) turbulence subject to the competing effects of global rotation and a perpendicular background magnetic field. We focus on the case of a strong background field and find that increasing the rotation rate from zero produces significant changes in the structure of the turbulent flow. Starting with a two-dimensional inverse cascade at zero rotation, the flow first transitions to a forward cascade of kinetic energy, then to a shear-layer dominated regime, and finally to a second shear-layer regime where the kinetic energy flux is strongly suppressed and the energy transfer is mediated by the induced magnetic field. We show that the first two transitions occur at distinct values of the Rossby number, and the third occurs at a distinct value of the Lehnert number. More generally, our results demonstrate that, when considering the simultaneous limits of strong rotation and a strong guide field, the order in which those limits are taken matters in the misaligned case.