Magnetic confinement of the solar tachocline: The oblique dipole

TL;DR

This study uses 3D MHD simulations to investigate whether a primordial magnetic field can confine the solar tachocline, finding that convective motions prevent such confinement regardless of magnetic field topology.

Contribution

The paper demonstrates through realistic simulations that magnetic confinement of the solar tachocline by primordial fields is ineffective due to convective motions.

Findings

Magnetic fields open into the convective envelope.

Magnetic torques establish isorotation law.

Convective motions prevent magnetic confinement.

Abstract

3D MHD global solar simulations coupling the turbulent convective zone and the radiative zone have been carried out. Essential features of the Sun such as differential rotation, meridional circulation and internal waves excitation are recovered. These realistic models are used to test the possibility of having the solar tachocline confined by a primordial inner magnetic field. We find that the initially confined magnetic fields we consider open into the convective envelope. Angular momentum is transported across the two zones by magnetic torques and stresses, establishing the so-called Ferarro's law of isorotation. In the parameter space studied, the confinement of the magnetic field by meridional circulation penetration fails, also implying the failure of the tachocline confinement by the magnetic field. Three-dimensional convective motions are proven responsible for the lack of magnetic field confinement. Those results are robust for the different magnetic field topologies considered, i.e. aligned or oblique dipole.