Call and Response: A Time-Resolved Study of Chromospheric Evaporation in a Large Solar Flare

TL;DR

This study provides a detailed, time-resolved analysis of chromospheric evaporation during a large X-class solar flare, linking energy injection to plasma responses across multiple temperatures.

Contribution

It offers the first comprehensive, time-resolved set of chromospheric diagnostics and energy injection profile for a major solar flare.

Findings

Explosive chromospheric evaporation driven by 4.8×10^{30} erg energy injection.

Correlation between peak electron injection and maximum plasma velocities.

Observation of unresolved flows near the flow reversal temperature.

Abstract

We studied an X1.6 solar flare produced by NOAA AR 12602 on 2014 October 22. The entirety of this event was covered by RHESSI, IRIS, and Hinode/EIS, allowing analysis of the chromospheric response to a nonthermal electron driver. We derived the energy contained in nonthermal electrons via RHESSI spectral fitting, and linked the time-dependent parameters of this call to the response in Doppler velocity, density, and nonthermal width across a broad temperature range. The total energy injected was $4.8\times10^{30}$ erg, and lasted $352$ seconds. This energy drove explosive chromospheric evaporation, with a delineation in both Doppler and nonthermal velocities at the flow reversal temperature, between 1.35--1.82 MK. The time of peak electron injection (14:06 UT) corresponded to the time of highest velocities. At this time, we found 200 km s$^{-1}$ blueshifts in the core of Fe XXIV, which is typically assumed to be at rest. Shortly before this time, the nonthermal electron population had the shallowest spectral index ($\approx$ 6), corresponding to the peak nonthermal velocity in Si IV and Fe XXI. Nonthermal velocities in Fe XIV, formed near the flow reversal temperature were low, and not correlated with density or Doppler velocity. Nonthermal velocities in ions with similar temperatures were observed to increase and correlate with Doppler velocities, implying unresolved flows surrounding the flow reversal point. This study provides a comprehensive, time-resolved set of chromospheric diagnostics for a large X-class flare, along with a time-resolved energy injection profile, ideal for further modeling studies.