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

TL;DR

This study investigates the mass and energy transfer during a solar flare by analyzing chromospheric evaporation and coronal rain using IRIS and AIA/SDO data, revealing their dynamics, morphology, and energetics.

Contribution

It provides detailed observational insights into the evolution and relationship of chromospheric evaporation and coronal rain during a flare, highlighting their roles in the solar flare mass-energy cycle.

Findings

CE speeds of 138 km/s with temperatures around 9 million K.

CR mass outflow is three times the CE inflow, indicating unresolved processes.

CR energy is about half of CE energy, emphasizing their interconnected roles.

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 \textit{IRIS} and \textit{AIA/SDO}, 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 \ion{Fe}{XXI} line with \textit{IRIS} and in the \ion{Fe}{XVIII} line of AIA, with upward average total speeds of $138\pm[35]~$km~s$^{-1}$ and a temperature of $[9.03\pm3.28]\times10^{6}$~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 increases by a factor of $\approx4.4$ and 6, respectively. The rain's velocity increases by a 1.4, in agreement with gas pressure drag. In contrast, the clump widths variation is negligible. The location and morphology of CE match closely those of the rain showers, with similar CE sub-structure 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 coronal rain in the mass-energy cycle of a flare.