Spoke-like differential rotation in a convective dynamo with a coronal envelope

TL;DR

This study presents four convective dynamo simulations with a coronal layer, revealing solar-like differential rotation, a multi-cellular meridional flow, and oscillatory magnetic fields with equatorward migration, advancing understanding of solar magnetic dynamics.

Contribution

The paper introduces self-consistent convective dynamo simulations including a coronal layer, demonstrating realistic differential rotation and magnetic field behaviors akin to the Sun.

Findings

Solar-like differential rotation with radial contours

Multi-cellular meridional circulation with poleward near-surface flow

Oscillatory magnetic fields with equatorward migration

Abstract

We report on the results of four convective dynamo simulations with an outer coronal layer. The magnetic field is self-consistently generated by the convective motions beneath the surface. Above the convection zone, we include a polytropic layer that extends to 1.6 solar radii. The temperature increases in this region to $\approx8$ times the value at the surface, corresponding to $\approx1.2$ times the value at the bottom of the spherical shell. We associate this region with the solar corona. We find solar-like differential rotation with radial contours of constant rotation rate, together with a near-surface shear layer. This non-cylindrical rotation profile is caused by a non-zero latitudinal entropy gradient that offsets the Taylor--Proudman balance through the baroclinic term. The meridional circulation is multi-cellular with a solar-like poleward flow near the surface at low latitudes. In most of the cases, the mean magnetic field is oscillatory with equatorward migration in two cases. In other cases, the equatorward migration is overlaid by stationary or even poleward migrating mean fields.