Dynamo Effects Near The Transition from Solar to Anti-Solar Differential Rotation

TL;DR

This study uses advanced 3D MHD simulations to explore how magnetic fields influence the transition from anti-solar to solar-like differential rotation in stellar convection zones, revealing magnetic reversal effects and flow morphology variations.

Contribution

It introduces a new anelastic simulation code and demonstrates magnetic field effects on differential rotation and convection patterns in buoyancy-dominated stellar regimes.

Findings

Magnetic fields can reverse anti-solar to solar-like differential rotation.

Convection flows are stronger in polar regions, leading to polar magnetic field concentration.

Different convection morphologies exist in inner and outer convection zone layers.

Abstract

Numerical MHD simulations play increasingly important role for understanding mechanisms of stellar magnetism. We present simulations of convection and dynamos in density-stratified rotating spherical fluid shells. We employ a new 3D simulation code for the solution of a physically consistent anelastic model of the process with a minimum number of parameters. The reported dynamo simulations extend into a "buoyancy-dominated" regime where the buoyancy forcing is dominant while the Coriolis force is no longer balanced by pressure gradients and strong anti-solar differential rotation develops as a result. We find that the self-generated magnetic fields, despite being relatively weak, are able to reverse the direction of differential rotation from anti-solar to solar-like. We also find that convection flows in this regime are significantly stronger in the polar regions than in the equatorial region, leading to non-oscillatory dipole-dominated dynamo solutions, and to concentration of magnetic field in the polar regions. We observe that convection has different morphology in the inner and at the outer part of the convection zone simultaneously such that organized geostrophic convection columns are hidden below a near-surface layer of well-mixed highly-chaotic convection. While we focus the attention on the buoyancy-dominated regime, we also demonstrate that conical differential rotation profiles and persistent regular dynamo oscillations can be obtained in the parameter space of the rotation-dominated regime even within this minimal model.