# Explosive chromospheric evaporation driven by nonthermal electrons around one footpoint of a solar flare loop

## TL;DR

This study presents combined spectral and imaging evidence of explosive chromospheric evaporation driven by nonthermal electrons during a solar flare, highlighting the temporal correlation between microwave/HXR emissions and Doppler velocities.

## Contribution

First to demonstrate chromospheric evaporation evidence from both spectral and imaging data in the same flare, linking nonthermal electrons to the evaporation process.

## Key findings

- Fe XXI shows blue shift indicating upflows in hot plasma.
- Si IV shows red shift indicating downflows in cooler plasma.
- Microwave and HXR pulses correlate with Doppler velocities, confirming electron-driven evaporation.

## Abstract

We explore the temporal relationship between microwave/HXR emission and Doppler velocity during the impulsive phase of a solar flare on 2014 October 27 (SOL2014-10-27), which displays a pulse on the light curves in microwave (34 GHz) and hard X-ray (HXR, 25-50 keV) bands before the flare maximum. Imaging observation shows that this pulse mainly comes from one footpoint of a solar flare loop. The slit of Interface Region Imaging Spectrograph (IRIS) stays at this footpoint during this solar flare. The Doppler velocities of Fe XXI 1354.09 A and Si IV 1402.77 A are extracted from the Gaussian fitting method. We find that the hot line of Fe XXI 1354.09 A (logT~7.05) in corona exhibits blue shift, while the cool line of Si IV 1402.77 A (logT~4.8) in transition region exhibits red shift, indicating explosive chromospheric evaporation. The evaporative upflows along the flare loop are also observed in the AIA 131 A image. To our knowledge, this is the first report of chromospheric evaporation evidence from both spectral and imaging observations in the same flare. Both microwave and HXR pulses are well correlated with the Doppler velocities, suggesting that the chromospheric evaporation is driven by nonthermal electrons around this footpoint of a solar flare loop.