Excitation of vertical coronal loop oscillations by plasma condensations

Centre for Fusion, Space and Astrophysics, Department of PhysicsUniversity of Warwick Coventry CV4 7AL UK
e-mail: p.kohutova@warwick.ac.uk

Received: 21 June 2017
Accepted: 16 August 2017

Abstract

Context. Coronal rain composed of downfalling cool plasma condensations occurs in thermally unstable loops as a consequence of catastrophic cooling. Such loops contain significant quantities of dense plasma out of hydrostatic equilibrium. Transverse oscillations traced by coronal rain blobs are often observed in rainy loops.

Aims. We aim to investigate the possibility of excitation of loop oscillations by the presence of condensation plasma.

Methods. We carried out 2.5D magnetohydrodynamic simulations of a coronal loop containing a cool and a dense condensation region near the loop apex and investigated the properties and evolution of the resulting oscillatory motion of the loop.

Results. The presence of dense condensation region at the apex of the coronal loop is found to excite fundamental harmonic of a vertically polarised kink mode. As the condensations fall towards the loop footpoints under the influence of gravity, the fundamental mode period decreases as a result of the change in distribution of mass along the loop.

Conclusions. We propose coronal rain as a possible excitation mechanism for transverse loop oscillations.