On-disk solar coronal condensations facilitated by magnetic reconnection between open and closed magnetic structures

TL;DR

This study reveals that magnetic reconnection between open and closed structures can facilitate on-disk coronal condensations and rain, providing new insights into the mass cycle in the solar corona.

Contribution

It demonstrates, through multi-viewpoint EUV observations, that on-disk condensations are linked to magnetic reconnection, a mechanism previously observed only off-limb.

Findings

Reconnection forms dips where condensations occur.

On-disk and off-limb observations show consistent condensation patterns.

Reconnection facilitates coronal rain formation on the solar disk.

Abstract

Coronal condensation and rain are a crucial part of the mass cycle between the corona and chromosphere. In some cases, condensation and subsequent rain originate in the magnetic dips formed during magnetic reconnection. This provides a new and alternative formation mechanism for coronal rain. Until now, only off-limb, rather than on-disk, condensation events during reconnection have been reported. In this paper, employing extreme-ultraviolet (EUV) images of the Solar Terrestrial Relations Observatory (STEREO) and Solar Dynamics Observatory (SDO), we investigate the condensations facilitated by reconnection from 2011 July 14 to 15, when STEREO was in quadrature with respect to the Sun-Earth line. Above the limb, in STEREO/EUV Imager (EUVI) 171 \AA~images, higher-lying open structures move downward, reconnect with the lower-lying closed loops, and form dips. Two sets of newly reconnected structures then form. In the dips, bright condensations occur in EUVI 304 \AA~images repeatedly which then flow downward to the surface. In the on-disk observations by SDO/Atmospheric Imaging Assembly (AIA) in the 171 \AA~channel, these magnetic structures are difficult to identify. Dark condensations appear in AIA 304 \AA~images, and then move to the surface as on-disk coronal rain. The cooling and condensation of coronal plasma is revealed by the EUV light curves. If only the on-disk observations would be available, the relation between the condensations and reconnection, shown clearly by the off-limb observations, would not be identified. Thus, we suggest that some on-disk condensation events seen in transition region and chromospheric lines may be facilitated by reconnection.