Nonlinear Evolution of Axisymmetric Twisted Flux Tubes in the Solar Tachocline

TL;DR

This study numerically investigates the nonlinear evolution of axisymmetric twisted flux tubes in the solar tachocline, revealing how twist influences stability and the destruction of magnetic fields.

Contribution

It demonstrates the effects of twist on flux tube stability and shows that twisted tubes can suppress shredding instabilities or evolve differently due to their non-equilibrium nature.

Findings

Untwisted flux tubes undergo radial-shredding instabilities.

Twisted flux tubes can suppress these instabilities.

Twisted tubes are generally not equilibrium solutions, leading to different evolution.

Abstract

We numerically study the evolution of magnetic fields and fluid flows in a thin spherical shell. We take the initial field to be a latitudinally confined, predominantly toroidal flux tube. For purely toroidal, untwisted flux tubes, we recover previously known radial-shredding instabilities, and show further that in the nonlinear regime these instabilities can very effectively destroy the original field. For twisted flux tubes, including also a poloidal component, there are several possibilities, including the suppression of the radial-shredding instability, but also a more directly induced evolution, brought about because twisted flux tubes in general are not equilibrium solutions of the governing equations.