A Model for Gradual Phase Heating Driven by MHD Turbulence in Solar Flares

TL;DR

This paper presents a one-dimensional MHD turbulence model that explains the prolonged heating observed during the gradual phase of solar flares, addressing the discrepancy between impulsive models and observations.

Contribution

It introduces a physically motivated model of extended flare heating driven by the dissipation of MHD turbulence generated during magnetic reconnection.

Findings

Simulated EUV light curves match observed decay times of tens of minutes.

Turbulent energy dissipation can sustain prolonged heating in flare loops.

Model provides a self-consistent mechanism linking reconnection to extended flare emission.

Abstract

Coronal flare emission is commonly observed to decay on timescales longer than those predicted by impulsively-driven, one-dimensional flare loop models. This discrepancy is most apparent during the gradual phase, where emission from these models decays over minutes, in contrast to the hour or more often observed. Magnetic reconnection is invoked as the energy source of a flare, but should deposit energy into a given loop within a matter of seconds. Models which supplement this impulsive energization with a long, persistent ad hoc heating have successfully reproduced long-duration emission, but without providing a clear physical justification. Here we propose a model for extended flare heating by the slow dissipation of turbulent Alfv\'en waves initiated during the retraction of newly-reconnected flux tubes through a current sheet. Using one-dimensional simulations, we track the production and evolution of MHD wave turbulence trapped by reflection from high-density gradients in the transition region. Turbulent energy dissipates through non-linear interaction between counter-propagating waves, modeled here using a phenomenological one-point closure model. AIA EUV light curves synthesized from the simulation were able to reproduce emission decay on the order of tens of minutes. We find this simple model offers a possible mechanism for generating the extended heating demanded by observed coronal flare emissions self-consistently from reconnection-powered flare energy release.