Solar Dynamo and Toroidal Field Instabilities

TL;DR

This paper reviews the properties of kink and quasi-interchange instabilities in solar magnetic fields, presents a mean-field dynamo model incorporating these effects, and discusses the solar cycle's possible driving mechanisms.

Contribution

It introduces a new perspective on the localization of instabilities and develops a mean-field dynamo model based on recent simulation results and observed solar shear layers.

Findings

Unstable modes are localized near the Equator, not the Poles.

Non-zero helicity can be generated at a non-linear stage.

A solar dynamo model with localized alpha-effect and meridional circulation is proposed.

Abstract

The possibility of non-axisimmetric (kink) instabilities of a toroidal field seated in the tachocline is much discussed in the literature. In this work, the basic properties of kink and quasi-interchange instabilities, produced by mixed toroidal and poloidal configuration, will be briefly reviewed. In particular it will be shown that the unstable modes are strongly localized near the Equator and not near the Poles as often claimed in the literature. Based on the results of recent numerical simulations, it is argued that a non-zero helicity can already be produced at a non-linear level. A mean-field solar dynamo is then constructed with a positive $\alpha$-effect in the overshoot layer localized near the Equator and a meridional circulation with a deep return flow. Finally, the possibility that the solar cycle is driven by a $\alpha\Omega$ dynamo generated by the negative subsurface shear in the supergranulation layer will also be discussed.