OBSERVING THE FORMATION OF FLARE-DRIVEN CORONAL RAIN

ABSTRACT 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 cool...

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Bibliographic Details
Published in:The Astrophysical journal 2016-12, Vol.833 (2), p.184
Main Authors: Scullion, E., Voort, L. Rouppe van der, Antolin, P., Wedemeyer, S., Vissers, G., Kontar, E. P., Gallagher, P. T.
Format: Article
Language:English
Subjects:
Acoustic waves
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Clumps
COMPARATIVE EVALUATIONS
Cooling
Cooling rate
Coronal loops
CROSS SECTIONS
DATA ANALYSIS
DENSITY
EMISSION
Emission measurements
ENTHALPY
EVAPORATION
Evaporative cooling
EXTREME ULTRAVIOLET RADIATION
MASS TRANSFER
Mathematical models
methods: data analysis
methods: observational
Numerical models
Periodic variations
PERIODICITY
PLASMA
RADIATIVE COOLING
Rain
STELLAR WINDS
Strands
techniques: image processing
techniques: spectroscopic
TELESCOPES
Travel time
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Summary:ABSTRACT 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 K and the observed properties between and 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.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/833/2/184