The Role of Magnetic Helicity in the Structure and Heating of the Sun's Corona

TL;DR

This paper presents a numerical simulation-based model explaining how magnetic helicity is transported in the solar corona, leading to the formation of filament channels and hot, smooth coronal loops, thus elucidating the corona's structure and heating.

Contribution

It introduces a novel model demonstrating magnetic helicity transport via reconnection, accounting for filament channel formation and coronal loop heating in the solar atmosphere.

Findings

Magnetic helicity accumulates above PILs forming filament channels.

Magnetic reconnection transports helicity, heating the corona.

Coronal loops remain smooth and hot due to helicity distribution.

Abstract

Two of the most important features of the solar atmosphere are its hot, smooth coronal loops and the concentrations of magnetic shear, known as filament channels, that reside above photospheric polarity inversion lines (PILs). The shear observed in filament channels represents magnetic helicity, while the smoothness of the coronal loops indicates an apparent lack of magnetic helicity in the rest of the corona. At the same time, models that attempt to explain the high temperatures observed in these coronal loops require magnetic energy, in the form of twist, to be injected at the photosphere. In addition to magnetic energy, this twist also represents magnetic helicity. Unlike magnetic energy, magnetic helicity is conserved under reconnection, and is consequently expected to accumulate and be observed in the corona. However, filament channels, rather than the coronal loops, are the locations in the corona where magnetic helicity is observed, and it manifests itself in the form of shear, rather than twist. This naturally raises the question: if magnetic helicity needs to be injected to heat coronal loops, why is it only observed in filament channels, while coronal loops are observed to be laminar and smooth? This thesis addresses this question using a series of numerical simulations that demonstrate that magnetic helicity is transported throughout the solar corona by magnetic reconnection in such a way that it accumulates above PILs, forming filament channels, and leaving the rest of the corona generally smooth. In the process, it converts magnetic energy into heat, accounting for the large observed temperatures. This thesis presents a model for the formation of filament channels in the solar corona and the presence of smooth, hot coronal loops, and shows how the transport of magnetic helicity throughout the solar corona by magnetic reconnection is responsible for both of these phenomena.