The Role of Magnetic Helicity in Coronal Heating

TL;DR

This paper demonstrates through simulations that magnetic helicity plays a key role in coronal heating, with the efficiency of heating depending weakly on the helicity preference of photospheric motions, supporting the helicity condensation model.

Contribution

The study provides the first numerical evidence that helicity condensation can naturally account for coronal heating and explores how helicity injection influences heating efficiency.

Findings

Helicity condensation leads to sufficient coronal heating in simulations.

Heating efficiency is weakly dependent on the net helicity preference.

Motions with zero helicity preference are most efficient at heating.

Abstract

One of the greatest challenges in solar physics is understanding the heating of the Sun's corona. Most theories for coronal heating postulate that free energy in the form of magnetic twist/stress is injected by the photosphere into the corona where the free energy is converted into heat either through reconnection or wave dissipation. The magnetic helicity associated with the twist/stress, however, is expected to be conserved and appear in the corona. In previous work we showed that helicity associated with the small-scale twists undergoes an inverse cascade via stochastic reconnection in the corona, and ends up as the observed large-scale shear of filament channels. Our ``helicity condensation'' model accounts for both the formation of filament channels and the observed smooth, laminar structure of coronal loops. In this paper, we demonstrate, using helicity- and energy-conserving numerical simulations of a coronal system driven by photospheric motions, that the model also provides a natural mechanism for heating the corona. We show that the heat generated by the reconnection responsible for the helicity condensation process is sufficient to account for the observed coronal heating. We study the role that helicity injection plays in determining coronal heating and find that, crucially, the heating rate is only weakly dependent on the net helicity preference of the photospheric driving. Our calculations demonstrate that motions with 100\% helicity preference are least efficient at heating the corona; those with 0\% preference are most efficient. We discuss the physical origins of this result and its implications for the observed corona.