The Role of Magnetic Helicity in Structuring the Solar Corona

TL;DR

This study uses numerical simulations to show how magnetic helicity injection by photospheric motions influences the formation of coronal features, linking prominences and smooth loops through helicity dynamics.

Contribution

It demonstrates that the structure of the solar corona is governed by the helicity preference of photospheric motions, revealing the role of magnetic helicity in coronal structuring.

Findings

Helicity condensation leads to prominence formation at polarity inversion lines.

Coronal loops become smooth and laminar due to helicity-driven reconnection.

The level of tangling in loops inversely correlates with net helicity injected.

Abstract

Two of the most widely observed and yet most puzzling features of the Sun's magnetic field are coronal loops that are smooth and laminar and prominences/filaments that are strongly sheared. These two features would seem to be quite unrelated in that the loops are near their minimum-energy current-free state, whereas filaments are regions of high magnetic stress and intense electric currents. We argue that, in fact, these two features are inextricably linked in that both are due to a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a \citet{Parker72} corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: 1) in agreement with the helicity condensation model of \citet{Antiochos13}, the inverse cascade of helicity by magnetic reconnection results in the formation of prominences/filaments localized about polarity inversion lines (PILs); 2) this same process removes most structure from the rest of the corona, resulting in smooth and laminar coronal loops; 3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and 4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.