Helicity-vorticity turbulent pumping of magnetic fields in solar convection zone

TL;DR

This paper investigates how helical convective motions and differential rotation in the solar convection zone cause a turbulent magnetic field drift, affecting the solar dynamo and sunspot activity patterns.

Contribution

It introduces a new mechanism of magnetic field transport driven by helicity-vorticity interactions, analyzed through mean-field magnetohydrodynamics and applied to solar dynamo modeling.

Findings

Helicity-vorticity pumping can reach several m/s near the convection zone base.

The effect influences sunspot drift patterns during solar cycles.

It modifies the features of the sunspot time-latitude diagram.

Abstract

We study the effect of turbulent drift of a large-scale magnetic field that results from the interaction of helical convective motions and differential rotation in the solar convection zone. The principal direction of the drift corresponds to the direction of the large-scale vorticity vector. Thus, the effect produces a latitudinal transport of the large-scale magnetic field in the convective zone wherever the angular velocity has a strong radial gradient. The direction of the drift depends on the sign of helicity and it is defined by the Parker-Yoshimura rule. The analytic calculations are done within the framework of mean-field magnetohydrodynamics using the minimal \tau-approximation. We estimate the magnitude of the drift velocity and find that it can be several m/s near the base of the solar convection zone. The implications of this effect for the solar dynamo are illustrated on the basis of an axisymmetric mean-field dynamo model with a subsurface shear layer. We find that the helicity--vorticity pumping effect can have an influence on the features of the sunspot time--latitude diagram, producing a fast drift of the sunspot activity maximum at the rise phase of the cycle and a slow drift at the decay phase of the cycle.