The effects of driving time scales on heating in a coronal arcade

TL;DR

This study uses 3D MHD simulations to explore how different photospheric driving time scales affect energy injection and heating in a coronal arcade, finding that slow, DC-like motions inject more energy and lead to higher plasma temperatures than wave-like, AC-driven motions.

Contribution

It demonstrates that longer time scale, DC-like footpoint motions are more effective at heating the corona than short time scale, wave-like motions, highlighting the importance of driving time scales in coronal heating models.

Findings

Long time scale motions inject more Poynting flux.

Slow stressing motions increase plasma temperature more.

Ohmic heating dominates over viscous heating.

Abstract

Context. The relative importance of AC and DC heating in maintaining the temperature of the corona is not well constrained. Aims. Investigate the effects of the characteristic time scales of photospheric driving on the injection and dissipation of energy within a coronal arcade. Methods. We have conducted three dimensional MHD simulations of foot point driving imposed on an arcade. We modified the typical driving time scales to understand the efficiency of heating obtained using AC and DC drivers. We considered the implications for the injected Poynting flux and the nature of the energy release in dissipative regimes. Results. For the same driver amplitude and complexity, long time scale motions are able to inject a much greater Poynting flux into the corona. Consequently, in non-ideal regimes, slow stressing motions result in a greater increase in plasma temperature than for wave-like driving. In dissipative simulations, Ohmic heating is found to be much more significant than viscous heating. For all drivers in our parameter space, energy dissipation is greatest close to the base of the arcade where the magnetic field strength is strongest and at separatrix surfaces, where the field connectivity changes. Across all simulations, the background field is stressed with random foot point motions (in a manner typical of DC heating studies) and even for short time scale driving, the injected Poynting flux is large given the small amplitude flows considered. For long time scale driving, the rate of energy injection was comparable to the expected requirements in active regions. The heating rates were found to scale with the perturbed magnetic field strength and not the total field strength. Conclusions. Alongside recent studies which show power within the corona is dominated by low frequency motions, our results suggest that in the closed corona, DC heating is more significant than AC heating.