Solar Flare Ion Temperatures
Abstract
This paper proposes that the ion temperature is several times the local electron temperature in the hot onset phase and at the above-the-loop region of solar flares. The paper considers: the evidence of spectral line Doppler widths ("non-thermal" broadening); evidence for "universal" ion and electron temperature increase scaling relations for magnetic reconnection in the solar wind, Earth's magnetopause, Earth's magnetotail and numerical simulations; and thermal equilibration times for onset and above-the-loop densities, which are much longer than previous estimates based on soft X-ray flare loops. We conclude that the ion temperature is likely to reach 60 MK or greater and that it may represent a substantial part of spectral line widths, significantly contributing to solving the long-standing issue of the excess nonthermal broadening in flare lines.
Cite
@article{arxiv.2509.01237,
title = {Solar Flare Ion Temperatures},
author = {Alexander J. B. Russell and Vanessa Polito and Paola Testa and Bart De Pontieu and Sergey A. Belov},
journal= {arXiv preprint arXiv:2509.01237},
year = {2025}
}
Comments
Accepted by ApJ Letters