Simulations of the Mg II k and Ca II 8542 lines from an Alfv\'en Wave-heated flare chromosphere

TL;DR

This study uses radiation hydrodynamic simulations to compare Alfvén wave heating and electron beam heating in solar flare chromospheres, finding observable differences in Mg II k-line emissions that can help identify the dominant heating mechanism.

Contribution

It introduces a detailed comparison of wave-heated and beam-heated chromospheric models, highlighting observable spectral differences in Mg II k-line profiles.

Findings

Mg II k-line profiles differ significantly between models and match observations.

Ca II 8542A profiles show minimal differences between models.

Wave heating produces more realistic Mg II k-line emissions.

Abstract

We use radiation hydrodynamic simulations to examine two models of solar flare chromospheric heating: Alfv\'en wave dissipation and electron beam collisional losses. Both mechanisms are capable of strong chromospheric heating, and we show that the distinctive atmospheric evolution in the mid-to-upper chromosphere results in Mg II k-line emission that should be observably different between wave-heated and beam-heated simulations. We also present Ca II 8542A profiles which are formed slightly deeper in the chromosphere. The Mg II k-line profiles from our wave-heated simulation are quite different from those from a beam-heated model and are more consistent with IRIS observations. The predicted differences between the Ca II 8542A in the two models are small. We conclude that careful observational and theoretical study of lines formed in the mid-to-upper chromosphere holds genuine promise for distinguishing between competing models for chromospheric heating in flares.