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

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 o...

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Bibliographic Details
Published in:The Astrophysical journal 2023-02, Vol.944 (2), p.147
Main Authors: Ashfield, William, Longcope, Dana
Format: Article
Language:English
Subjects:
Alfven waves
Astrophysics
Atmospheric models
Current sheets
Decay
Density gradients
Dissipation
Emission
Energy
Energy sources
Heating
Light curve
Magnetic reconnection
Magnetohydrodynamic turbulence
Magnetohydrodynamic waves
Magnetohydrodynamical simulations
Modelling
Solar corona
Solar extreme ultraviolet emission
Solar flares
Tubes
Turbulent energy
Wave propagation
Wave reflection
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Summary: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 Alfvén 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 nonlinear interaction between counter-propagating waves, modeled here using a phenomenological one-point closure model. Atmospheric Imaging Assembly 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.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/acb1b2