3-D non-linear evolution of a magnetic flux tube in a spherical shell: the isentropic case

TL;DR

This paper uses 3-D MHD simulations in spherical geometry to study the non-linear evolution of magnetic flux tubes in the solar convection zone, revealing mechanisms of flux emergence and effects of twist and rotation.

Contribution

It extends previous Cartesian studies by confirming flux tube splitting, identifying poleward-slip instability, and analyzing the impact of rotation on flux tube dynamics in spherical geometry.

Findings

Flux tubes split into two vortices if not twisted.

Twisted tubes exhibit poleward-slip instability.

Rotation reduces the rise velocity of flux tubes.

Abstract

We present recent 3-D MHD numerical simulations of the non-linear dynamical evolution of magnetic flux tubes in an adiabatically stratified convection zone in spherical geometry, using the anelastic spherical harmonic (ASH) code. We seek to understand the mechanism of emergence of strong toroidal fields from the base of the solar convection zone to the solar surface as active regions. We confirm the results obtained in cartesian geometry that flux tubes that are not twisted split into two counter vortices before reaching the top of the convection zone. Moreover, we find that twisted tubes undergo the poleward-slip instability due to an unbalanced magnetic curvature force which gives the tube a poleward motion both in the non-rotating and in the rotating case. This poleward drift is found to be more pronounced on tubes originally located at high latitudes. Finally, rotation is found to decrease the rise velocity of the flux tubes through the convection zone, especially when the tube is introduced at low latitudes.