Simultaneous Observations of Chromospheric Evaporation and Condensation during a C-class Flare

TL;DR

This study presents multi-instrument observations of chromospheric evaporation and condensation during a C6.7 flare, revealing slow downflows and fast upflows driven by nonthermal electrons, confirming explosive evaporation during the impulsive phase.

Contribution

First simultaneous observation of chromospheric evaporation and condensation during a C-class flare using multiple instruments, linking plasma flows to nonthermal electron activity.

Findings

Detected slow downflows (~15-19 km/s) in cool lines indicating chromospheric condensation.

Observed high-velocity upflows (~126-210 km/s) in EUV images indicating chromospheric evaporation.

Linked explosive evaporation to nonthermal electron activity evidenced by HXR/microwave pulses and radio bursts.

Abstract

We explored simultaneous observations of chromospheric evaporation and condensation during the impulsive phase of a C6.7 flare on 9 May 2019. The solar flare was simultaneously observed by multiple instruments, i.e., the New Vacuum Solar Telescope (NVST), the Interface Region Imaging Spectrograph, the Atmospheric Imaging Assembly (AIA), the Fermi, the Mingantu Spectral Radioheliograph, and the Nobeyama Radio Polarimeters. Using the single Gaussian fitting and the moment analysis technique, redshifted velocities at slow speeds of 15-19 km/s are found in the cool lines of C II and Si IV at one flare footpoint location. Red shifts are also seen in the H-alpha line-of-sight (LOS) velocity image measured by the NVST at double footpoints. Those red shifts with slow speeds can be regarded as the low-velocity downflows driven by the chromospheric condensation. Meanwhile, the converging motions from double footpoints to the loop top are found in the high-temperature EUV images, such as AIA 131 A, 94 A, and 335 A. Their apparent speeds are estimated to be roughly 126-210 km/s, which could be regarded as the high-velocity upflows caused by the chromospheric evaporation. The nonthermal energy flux is estimated to be about 5.7x10^10 erg/s/cm^2. The characteristic timescale is roughly equal to 1 minute. All these observational results suggest an explosive chromospheric evaporation during the flare impulsive phase. While a HXR/microwave pulse and a type III radio burst are found simultaneously, indicating that the explosive chromospheric evaporation is driven by the nonthermal electron.