The Origin of Solar Activity in the Tachocline

TL;DR

This paper investigates the stability of the solar tachocline and suggests that magneto-rotational turbulence limits magnetic dynamo activity to near the equator, explaining the latitudinal distribution of solar active regions.

Contribution

It introduces a stability analysis of the tachocline's magneto-rotational properties, linking turbulence to the latitudinal restriction of solar magnetic activity.

Findings

Tachocline is unstable above 37 degrees latitude.

Turbulence prevents dynamo action away from the equator.

Active regions are confined within 35 degrees of the equator.

Abstract

Solar active regions, produced by the emergence of tubes of strong magnetic field in the photosphere, are restricted to within 35 degrees of the solar equator. The nature of the dynamo processes that create and renew these fields, and are therefore responsible for solar magnetic phenomena, are not well understood. We analyze the magneto-rotational stability of the solar tachocline for general field geometry. This thin region of strong radial and latitudinal differential rotation, between the radiative and convective zones, is unstable at latitudes above 37 degrees, yet is stable closer to the equator. We propose that small-scale magneto-rotational turbulence prevents coherent magnetic dynamo action in the tachocline except in the vicinity of the equator, thus explaining the latitudinal restriction of active regions. Tying the magnetic dynamo to the tachocline elucidates the physical conditions and processes relevant to solar magnetism.