Angular momentum transport by magnetoconvection and the magnetic modulation of the solar differential rotation

TL;DR

This paper uses simulations of rotating magnetoconvection to explore how magnetic fields influence the solar differential rotation, revealing conditions under which magnetic effects flatten the rotation profile and cause spin-down.

Contribution

It introduces a simulation framework for analyzing angular momentum transport in magnetoconvection with inclined magnetic fields, highlighting the magnetic modulation of solar differential rotation.

Findings

Magnetic stresses depend on field component signs without rotation.

Reynolds stresses dominate angular momentum transport at high rotation rates.

Magnetic effects flatten the rotation profile and cause equatorial spin-down under certain conditions.

Abstract

In order to explain the variance of the solar rotation law during the activity minima and maxima, the angular momentum transport by rotating magnetoconvection is simulated in a convective box penetrated by an inclined azimuthal magnetic field. Turbulence-induced kinetic and magnetic stresses { and} the Lorentz force of the large-scale magnetic background field are the basic transporters of angular momentum. Without rotation, the sign of the magnetic stresses naturally depends on the signs of the field components as positive (negative) $B_\theta B_\phi$ transport the angular momentum poleward (equatorward). For fast enough rotation, however, the turbulence-originated Reynolds stresses start to dominate the transport of the angular momentum flux. The simulations show that positive ratios of the two meridional magnetic field components to the azimuthal field reduce the inward radial as well as the equatorward latitudinal transport,%by the rotating magnetoconvection which result from hydrodynamic calculations. Only for $B_\theta B_\phi>0$ (generated by solar-type rotation laws with an accelerated equator) does the magnetic-influenced rotation at the solar surface prove to be flatter than the nonmagnetic profile together with the observed slight spin-down of the equator. The latter phenomenon does not appear for antisolar rotation with polar vortex as well as for rotation laws with prevailing radial shear.