Three-Dimensional Simulations of Solar and Stellar Dynamos: The Influence of a Tachocline

TL;DR

This paper reviews recent 3D simulations of solar and stellar dynamos, highlighting the role of the tachocline in magnetic flux organization, amplification, and field stability, using the ASH code.

Contribution

It presents the first global-scale solar convection simulations showing magnetic flux pumping into a tachocline and its effects on magnetic field organization and stability.

Findings

Tachocline promotes mean toroidal flux generation.

Enhances and stabilizes poloidal magnetic fields.

Results in more helical magnetic fields with hemispheric sign reversal.

Abstract

We review recent advances in modeling global-scale convection and dynamo processes with the Anelastic Spherical Harmonic (ASH) code. In particular, we have recently achieved the first global-scale solar convection simulations that exhibit turbulent pumping of magnetic flux into a simulated tachocline and the subsequent organization and amplification of toroidal field structures by rotational shear. The presence of a tachocline not only promotes the generation of mean toroidal flux, but it also enhances and stabilizes the mean poloidal field throughout the convection zone, promoting dipolar structure with less frequent polarity reversals. The magnetic field generated by a convective dynamo with a tachocline and overshoot region is also more helical overall, with a sign reversal in the northern and southern hemispheres. Toroidal tachocline fields exhibit little indication of magnetic buoyancy instabilities but may be undergoing magneto-shear instabilities.