Observing the formation of flare-driven coronal rain

E. Scullion, L. Rouppe Van Der Voort, P. Antolin, S. Wedemeyer, G. Vissers, E. P. Kontar, P. Gallagher

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)

Abstract

Flare-driven coronal rain can manifest from rapidly cooled plasma condensations near coronal loop-tops in thermally unstable post-flare arcades. We detect 5 phases that characterise the post-flare 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 s 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 co-moving, multi-thermal rain clumps that undergo catastrophic cooling from ~1 MK to ~22000 K. During catastrophic cooling the plasma cools at a maximum rate of 22700 K s-1 in multiple loop-top sources. We calculated the density of the EUV plasma from the DEM of the multi-thermal source employing regularised inversion. Assuming a pressure balance, we estimate the density of the chromospheric component of rain to be 9.21x1011 ±1.76x1011 cm-3 which is comparable with quiescent coronal rain densities. With up to 8 parallel strands in the EUV loop cross section, we calculate the mass loss rate from the post-flare arcade to be as much as 1.98x1012 ± 4.95x1011 g s-1. Finally, we reveal a close proximity between the model predictions of 105.8 K and the observed properties between 105.9 K and 106.2 K, that 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.
Original languageEnglish
Article number184
Number of pages24
JournalAstrophysical Journal
Volume833
Issue number2
Early online date16 Dec 2016
DOIs
Publication statusPublished - 20 Dec 2016

Keywords

  • Sun
  • Methods: observational
  • Methods: data analysis
  • Techniques: image processing
  • Techniques: spectroscopic
  • Telescopes

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