Solar Flare Chromospheric Line Emission: Comparison Between IBIS High-resolution Observations and Radiative Hydrodynamic Simulations

TL;DR

This study compares high-resolution solar flare observations with radiative hydrodynamic simulations, revealing general agreement but also highlighting the need for refined energy input modeling to better match observed spectral line profiles.

Contribution

First direct comparison of IBIS high-resolution spectral observations with RADYN simulations for a solar flare, linking observed chromospheric emission to modeled plasma heating processes.

Findings

Synthetic Ca II 8542 Å profile matches observations well.

Synthetic Hα profile is fainter in the core than observed.

Hα emission is more sensitive to non-thermal electron flux.

Abstract

Solar flares involve impulsive energy release, which results in enhanced radiation over a broad spectral range and a wide range of heights. In particular, line emission from the chromosphere can provide critical diagnostics of plasma heating processes. Thus, a direct comparison between high-resolution spectroscopic observations and advanced numerical modeling results could be extremely valuable, but has not yet been attempted. In this paper, we present in this paper such a self-consistent investigation of an M3.0 flare observed by the Dunn Solar Telescope's Interferometric Bi-dimensional Spectrometer (IBIS) on 2011 September 24 which we have modeled with the radiative hydrodynamic code RADYN. We obtained images and spectra of the flaring region with IBIS in H$\alpha$ 6563 \AA\ and Ca II 8542 \AA, and with the Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) in X-rays. The latter observations were used to infer the non-thermal electron population, which was passed to RADYN to simulate the atmospheric response to electron collisional heating. We then synthesized spectral lines and compared their shapes and intensities to those observed by IBIS and found a general agreement. In particular, the synthetic Ca II 8542 \AA\ profile fits well to the observed profile, while the synthetic H$\alpha$ profile is fainter in the core than for the observation. This indicates that H$\alpha$ emission is more responsive to the non-thermal electron flux than the Ca II 8542 \AA\ emission. We suggest that it is necessary to refine the energy input and other processes is necessary to resolve this discrepancy.