On-disk coronal rain

TL;DR

This study analyzes on-disk coronal rain using high-resolution H-alpha observations, revealing that these cool, dense blobs share characteristics with off-limb coronal rain, and discusses their formation, morphology, and thermodynamics.

Contribution

First detailed statistical analysis of on-disk coronal rain, demonstrating its similarities to off-limb coronal rain and supporting its identification as the same phenomenon.

Findings

On-disk coronal rain shares morphological and dynamical properties with off-limb coronal rain.

Detection challenges are due to small size, faintness, and projection effects.

On-disk coronal rain likely plays a role in solar atmospheric dynamics.

Abstract

Small and elongated, cool and dense blob-like structures are being reported with high resolution telescopes in physically different regions throughout the solar atmosphere. Their detection and the understanding of their formation, morphology and thermodynamical characteristics can provide important information on their hosting environment, especially concerning the magnetic field, whose understanding constitutes a major problem in solar physics. An example of such blobs is coronal rain, a phenomenon of thermal non- equilibrium observed in active region loops, which consists of cool and dense chromospheric blobs falling along loop-like paths from coronal heights. So far, only off-limb coronal rain has been observed and few reports on the phenomenon exist. In the present work, several datasets of on-disk H{\alpha} observations with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish 1-m Solar Telescope (SST) are analyzed. A special family of on-disk blobs is selected for each dataset and a statistical analysis is carried out on their dynamics, morphology and temperatures. All characteristics present distributions which are very similar to reported coronal rain statistics. We discuss possible interpretations considering other similar blob-like structures reported so far and show that a coronal rain interpretation is the most likely one. Their chromospheric nature and the projection effects (which eliminate all direct possibility of height estimation) on one side, and their small sizes, fast dynamics, and especially, their faint character (offering low contrast with the background intensity) on the other side, are found as the main causes for the absence until now of the detection of this on-disk coronal rain counterpart.