Modeling the Subsurface Evolution of Active Region Flux Tubes

TL;DR

This paper uses 3D MHD simulations to study how active region flux tubes rise in the solar interior, revealing constraints on initial twist for proper tilt and showing asymmetries caused by Coriolis forces.

Contribution

It provides new insights into the initial conditions and asymmetries of subsurface flux tubes, improving understanding of their emergence and tilt angles.

Findings

Leading leg has stronger, more cohesive magnetic fields.

Asymmetry in flux tube twist and strength develops due to Coriolis force.

Results constrain initial twist for realistic tilt angles.

Abstract

I present results from a set of 3D spherical-shell MHD simulations of the buoyant rise of active region flux tubes in the solar interior which put new constraints on the initial twist of the subsurface tubes in order for them to emerge with tilt angles consistent with the observed Joy's law for the mean tilt of solar active regions. Due to the asymmetric stretching of the $\Omega$-shaped tube by the Coriolis force, a field strength asymmetry develops with the leading side having a greater field strength and thus being more cohesive compared to the following side. Furthermore, the magnetic flux in the leading leg shows more coherent values of local twist $\alpha \equiv {\bf J} \cdot {\bf B} / B^2$, whereas the values in the following leg show large fluctuations and are of mixed signs.