Filament Channel Formation Via Magnetic Helicity Condensation

TL;DR

This paper uses 3D MHD simulations to demonstrate how magnetic helicity condensation leads to the formation of filament channels with shear and helicity accumulation at solar PILs, supporting a specific formation model.

Contribution

It provides the first detailed numerical validation of the magnetic helicity condensation model for filament channel formation in the solar atmosphere.

Findings

Helicity inverse-cascades to large scales in simulations.

Sheared magnetic field lines form at PILs consistent with observations.

Quantitative agreement with the helicity-condensation model.

Abstract

A major unexplained feature of the solar atmosphere is the accumulation of magnetic shear, in the form of filament channels, at photospheric polarity inversion lines (PILs). In addition to free energy, this shear also represents magnetic helicity, which is conserved under reconnection. In this paper, we address the problem of filament channel formation and show how they acquire their shear and magnetic helicity. The results of 3D simulations using the Adaptively Refined Magnetohydrodynamics Solver (ARMS) are presented that support the model of filament channel formation by magnetic helicity condensation developed by \citet{Antiochos13}. We consider the supergranular twisting of a quasi-potential flux system that is bounded by a PIL and contains a coronal hole (CH). The magnetic helicity injected by the small-scale photospheric motions is shown to inverse-cascade up to the largest allowable scales that define the closed flux system: the PIL and the CH. This process produces field lines that are both sheared and smooth, and are sheared in opposite senses at the PIL and the CH. The accumulated helicity and shear flux are shown to be in excellent quantitative agreement with the helicity-condensation model. We present a detailed analysis of the simulations, including comparisons of our analytical and numerical results, and discuss their implications for observations.