From Chromospheric Evaporation to Coronal Rain: An Investigation of the Mass and Energy Cycle of a Flare

Abstract

Chromospheric evaporation (CE) and coronal rain (CR) represent two crucial phenomena encompassing the circulation of mass and energy during solar flares. While CE marks the start of the hot inflow into the flaring loop, CR marks the end, indicating the outflow in the form of cool and dense condensations. With the Interface Region Imaging Spectrograph (IRIS) and the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory, we examine and compare the evolution, dynamics, morphology, and energetics of the CR and CE during a C2.1 flare. The CE is directly observed in imaging and spectra in the Fe xxi line with IRIS and in the Fe xviii line of AIA, with upward average total speeds of 138 ± 35 km s−1 and a temperature of 9.03 ± 3.28 × 106 K. An explosive-to-gentle CE transition is observed, with an apparent reduction in turbulence. From quiescent to gradual flare phase, the amount and density of CR increase by a factor of ≈4.4 and 6, respectively. The rain’s velocity increases by a factor of 1.4, in agreement with gas pressure drag. In contrast, the clump width variation is negligible. The location and morphology of CE match closely those of the rain showers, with similar CE substructure to the rain strands, reflecting fundamental scales of mass and energy transport. We obtain a CR outflow mass three times larger than the CE inflow mass, suggesting the presence of unresolved CE, perhaps at higher temperatures. The CR energy corresponds to half that of the CE. These results suggest an essential role of CR in the mass−energy cycle of a flare.