The effects of driving time scales on coronal heating in a stratified atmosphere

TL;DR

This study uses 3D MHD simulations to explore how different driving time scales and amplitudes influence coronal heating, revealing that DC driving injects more energy and produces larger currents, while AC driving results in more frequent, shorter energy release events.

Contribution

It provides a comparative analysis of AC and DC coronal heating mechanisms considering various driving time scales and amplitudes using detailed 3D MHD simulations.

Findings

DC driving leads to higher energy injection and temperatures.

AC driving causes more frequent, shorter energy release events.

Higher velocity driving increases currents and coronal volume occupied.

Abstract

Aims: We investigate the atmospheric response to coronal heating driven by random flows with different characteristic time scales and amplitudes. Methods: We conducted a series of 3D MHD simulations of random driving imposed on a gravitationally stratified model of the solar atmosphere. In order to understand differences between alternating current (AC) and direct current (DC) heating, we considered the effects of changing the characteristic time scales of the imposed velocities. We also investigated the effects of the magnitude of the velocity driving. Results: Complex foot point motions lead to a proliferation of current sheets and energy dissipation throughout the corona. For a given amplitude, DC driving typically leads to a greater rate of energy injection when compared to AC driving. This leads to the formation of larger currents, increased heating rates and higher temperatures in DC simulations. There is no difference in the spatial distribution of energy dissipation across simulations, however, energy release events in AC cases tend to be more frequent and last for less time. Higher velocity driving is associated with larger currents, higher temperatures and the corona occupying a larger fraction of the simulation volume. In all cases, most of heating is associated with small energy release events, which occur much more frequently than large events. Conclusions: When combined with observational results showing a greater abundance of power in low frequency modes, these findings suggest that energy release in the corona is likely to be driven by long time scale motions. In the corona, AC and DC driving will occur concurrently and their effects remain difficult to isolate. The distribution of field line temperatures and the asymmetry of temperature profiles may reveal the frequency and longevity of energy release events and therefore the relative importance of AC and DC heating.