Optimal Electron Energies for Driving Chromospheric Evaporation in Solar Flares

TL;DR

This paper investigates how electron energy levels influence chromospheric evaporation regimes in solar flares, revealing that lower energy electrons can induce explosive evaporation more efficiently under certain conditions.

Contribution

It demonstrates the significance of electron energy and heating duration on evaporation regimes, refining the understanding of energy deposition in solar flare models.

Findings

Lower energy electrons are more efficient at heating the atmosphere in gentle evaporation.

The threshold between explosive and gentle evaporation depends on electron energy and heating duration.

Weaker beams can cause explosive evaporation at low electron energies.

Abstract

In the standard model of solar flares, energy deposition by a beam of electrons drives strong chromospheric evaporation leading to a significantly denser corona and much brighter emission across the spectrum. Chromospheric evaporation was examined in great detail by Fisher, Canfield, & McClymont (1985a,b,c), who described a distinction between two different regimes, termed explosive and gentle evaporation. In this work, we examine the importance of electron energy and stopping depths on the two regimes and on the atmospheric response. We find that with explosive evaporation, the atmospheric response does not depend strongly on electron energy. In the case of gentle evaporation, lower energy electrons are significantly more efficient at heating the atmosphere and driving up-flows sooner than higher energy electrons. We also find that the threshold between explosive and gentle evaporation is not fixed at a given beam energy flux, but also depends strongly on the electron energy and duration of heating. Further, at low electron energies, a much weaker beam flux is required to drive explosive evaporation.