Excitation and evolution of vertically polarised transverse loop oscillations by coronal rain

Department of Physics, University of Warwick, Coventry CV4 7AL, UK
e-mail: Erwin.Verwichte@warwick.ac.uk

Received: 22 February 2017
Accepted: 31 March 2017

Abstract

Context. Coronal rain is composed of cool dense blobs that form in solar coronal loops and are a manifestation of catastrophic cooling linked to thermal instability. The nature and excitation of oscillations associated with coronal rain is not well understood.

Aims. We consider observations of coronal rain in a bid to elucidate the excitation mechanism and evolution of wave characteristics.

Methods. We analyse IRIS and Hinode/SOT observations of an oscillating coronal rain event on the 17th Aug. 2014 and determine the wave characteristics as a function of time using tried and tested time-space analysis techniques.

Results. We exploit the seismological capability of the oscillation to deduce the relative rain mass from the oscillation amplitude. This is consistent with the evolution of the oscillation period showing the loop losing a third of its mass due to falling coronal rain in a 10−15 min time period.

Conclusions. We present the first evidence of the excitation of vertically polarised transverse loop oscillations triggered by catastrophic cooling at the loop top and consistent with two thirds of the loop mass being comprised of cool rain mass.