On the cause of solar-like equatorward migration in global convective dynamo simulations

TL;DR

This paper investigates the origin of equatorward magnetic field migration in stellar dynamo simulations, demonstrating it results from an $ ext{alpha} ext{Omega}$ dynamo wave consistent with the Parker--Yoshimura rule, driven by specific shear and $ ext{alpha}$ effects.

Contribution

The study provides a detailed explanation for equatorward migration in convective dynamo simulations, linking it to the $ ext{alpha} ext{Omega}$ dynamo wave mechanism and specific shear and $ ext{alpha}$ effects.

Findings

Migration direction explained by $ ext{alpha} ext{Omega}$ dynamo wave

Positive $ ext{alpha}$ effect in the north, negative in the south

Negative radial shear correlates with equatorward propagation

Abstract

We present results from four convectively-driven stellar dynamo simulations in spherical wedge geometry. All of these simulations produce cyclic and migrating mean magnetic fields. Through detailed comparisons we show that the migration direction can be explained by an $\alpha\Omega$ dynamo wave following the Parker--Yoshimura rule. We conclude that the equatorward migration in this and previous work is due to a positive (negative) $\alpha$ effect in the northern (southern) hemisphere and a negative radial gradient of $\Omega$ outside the inner tangent cylinder of these models. This idea is supported by a strong correlation between negative radial shear and toroidal field strength in the region of equatorward propagation.