Formation of coronal rain triggered by impulsive heating associated with magnetic reconnection

TL;DR

This paper presents observations showing that impulsive heating from magnetic reconnection can trigger coronal rain formation, expanding the understanding beyond standard models that assume steady, footpoint-localized heating.

Contribution

It demonstrates that magnetic reconnection-induced impulsive heating can initiate thermal instability and coronal rain formation along coronal loops, a process not previously emphasized.

Findings

Magnetic reconnection releases twist and causes impulsive heating.

Coronal rain forms following reconnection-induced heating.

Thermal instability can be triggered anywhere along a magnetic field line.

Abstract

Coronal rain consists of cool plasma condensations formed in coronal loops as a result of thermal instability. The standard models of coronal rain formation assume that the heating is quasi-steady and localised at the coronal loop footpoints. We present an observation of magnetic reconnection in the corona and the associated impulsive heating triggering formation of coronal rain condensations. We analyse combined SDO/AIA and IRIS observations of a coronal rain event following a reconnection between threads of a low-lying prominence flux rope and surrounding coronal field lines. The reconnection of the twisted flux rope and open field lines leads to a release of magnetic twist. Evolution of the emission of one of the coronal loops involved in the reconnection process in different AIA bandpasses suggests that the loop becomes thermally unstable and is subject to the formation of coronal rain condensations following the reconnection and that the associated heating is localised in the upper part of the loop leg. We conclude that in addition to the standard models of thermally unstable coronal loops with heating localised exclusively in the footpoints, thermal instability and subsequent formation of condensations can be triggered by the impulsive heating associated with magnetic reconnection occurring anywhere along a magnetic field line.