# Spectroscopic Analysis and RHD Modeling of the First Ca II H and Hϵ Flare Spectra from DKIST/ViSP

## TL;DR

This paper presents the first high-resolution observations of solar flare spectra from DKIST/ViSP and compares them with simulations to better understand flare dynamics.

## Contribution

The study provides the first flare-time DKIST observations of Ca II H and Hϵ lines and highlights model limitations in capturing their spectral features.

## Key findings

- The models reproduce some spectral features but fail to capture the width of Ca II H in the red wing.
- The relative intensity of Ca II H to Hϵ is not accurately reproduced by the simulations.
- Hϵ widths and intensities are influenced by deeper flare layers, not just the upper chromosphere.

## Abstract

We analyze decay phase observations of the GOES class C6.7 flare SOL2022-08-19T20:31 by the Visible Spectropolarimeter (ViSP) on the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST). The data include the first flare-time DKIST observations of the chromospheric Ca II H 396.8 nm and H\documentclass[12pt]{minimal}
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\begin{document}$\epsilon $\end{document}ϵ 397.0 nm spectral lines. These diagnostics have rarely been studied together during the modern era of high-resolution solar flare observations, and never at the spectral and spatial resolution of the DKIST. We directly compare DKIST spectra to state-of-the-art RADYN+RH simulations, including one heated by a nonthermal electron beam and one by in-situ thermal conduction. While certain salient properties of the spectra such as the width of H\documentclass[12pt]{minimal}
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\begin{document}$\epsilon $\end{document}ϵ are reproduced, the models severely underestimate the width of Ca II H in the red wing and fail to reproduce the exact relative intensity of Ca II H to H\documentclass[12pt]{minimal}
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\begin{document}$\epsilon $\end{document}ϵ. The models exhibit a range of chromospheric electron densities spanning over an order of magnitude. Unlike the modeled lower-order Balmer-series lines, we find that the width of H\documentclass[12pt]{minimal}
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\begin{document}$\epsilon $\end{document}ϵ is not solely related to the high-density upper chromosphere; the widths and intensities are also sensitive to the deeper flare layers. We outline possible avenues towards improvement of flare models, such as a comprehensive evaluation of flare heating mechanisms in the context of both impulsive and decay phase high-resolution data.