Observing the formation of flare-driven coronal rain

Scullion, E., Rouppe van der Voort, L., Antolin, P., Wedemeyer, S., Vissers, G., Kontar, E.P. and Gallagher, P.T. (2016) Observing the formation of flare-driven coronal rain. Astrophysical Journal, 833(2), 184. (doi:10.3847/1538-4357/833/2/184)

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Flare-driven coronal rain can manifest from rapidly cooled plasma condensations near coronal loop tops in thermally unstable postflare arcades. We detect five phases that characterize the postflare decay: heating, evaporation, conductive cooling dominance for ∼120 s, radiative/enthalpy cooling dominance for ∼4700 s, and finally catastrophic cooling occurring within 35–124 s, leading to rain strands with a periodicity of 55–70 s. We find an excellent agreement between the observations and model predictions of the dominant cooling timescales and the onset of catastrophic cooling. At the rain-formation site, we detect comoving, multithermal rain clumps that undergo catastrophic cooling from ∼1 MK to ∼22,000 K. During catastrophic cooling, the plasma cools at a maximum rate of 22,700 K s−1 in multiple loop-top sources. We calculated the density of the extreme-ultraviolet (EUV) plasma from the differential emission measure of the multithermal source employing regularized inversion. Assuming a pressure balance, we estimate the density of the chromospheric component of rain to be 9.21 × 1011± 1.76 × 1011 cm−3 , which is comparable with quiescent coronal rain densities. With up to eight parallel strands in the EUV loop cross section, we calculate the mass loss rate from the postflare arcade to be as much as 1.98 × 1012± 4.95 × 1011 g s−1 . Finally, we reveal a close proximity between the model predictions of 105.8 K and the observed properties between 105.9 and 106.2 K, which defines the temperature onset of catastrophic cooling. The close correspondence between the observations and numerical models suggests that indeed acoustic waves (with a sound travel time of 68 s) could play an important role in redistributing energy and sustaining the enthalpy-based radiative cooling.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Kontar, Professor Eduard
Authors: Scullion, E., Rouppe van der Voort, L., Antolin, P., Wedemeyer, S., Vissers, G., Kontar, E.P., and Gallagher, P.T.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:IOP Publishing
ISSN (Online):1538-4357
Published Online:16 December 2016
Copyright Holders:Copyright © 2016 The American Astronomical Society
First Published:First published in Astrophysical Journal 833(2): 184
Publisher Policy:Reproduced in accordance with the publisher copyright policy
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