On the Origin of Solar Hemispheric Helicity Rules: Rise of 3D Magnetic Flux Concentrations through a Background Magnetic Field

TL;DR

This paper investigates how 3D magnetic flux concentrations rise through a background magnetic field, revealing a mechanism that explains the solar hemispheric helicity rules by considering the twist orientation and tension forces in three dimensions.

Contribution

It extends previous 2.5D models to full 3D, demonstrating that the flux emergence selection mechanism persists and elucidating the role of tension forces in this process.

Findings

The twist orientation affects flux emergence likelihood.

The 3D dynamics reinforce the hemispheric helicity rules.

Tension forces play a key role in flux concentration behavior.

Abstract

Sunspots and active regions observed on the solar surface are widely believed to be manifestations of compact predominantly-toroidal magnetic field structures (``flux tubes") that emerge by magnetic buoyancy from the deeper interior of the Sun. Much work has examined the evolution of such magnetic structures, typically considering them as idealized isolated magnetic entities and not as more realistic magnetic concentrations in a volume-filling background magnetic field. Here, we report results that explore the buoyant rise dynamics of magnetic concentrations in a volume-filling field in the full three dimensions. Earlier 2.5D work in this series (arXiv:1805.08806, arXiv:2101.03472, arXiv:2204.13078) established the remarkable fact that the twist orientation of a flux concentration relative to the background field affected it's likelihood to rise and emerge, regardless of whether the buoyant rise took place in the absence or presence of convection. The contrasting dynamics between structures with differing orientations leads to a selection mechanism that reproduces characteristics of the ``solar hemispheric helicity rule(s)" (SHHR) observations strikingly well. Here, we show that this two-dimensional selection mechanism persists in the face of the added complexity of three-dimensional dynamics. Arching of the magnetic structure in the third dimension, as might be expected in the solar application, is introduced. The role of tension force leading to this selection mechanism is elucidated and subtle differences that arise due to the three-dimensional geometry are discussed.