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arXiv · 2509.01237

Solar Flare Ion Temperatures

Alexander J. B. Russell·Vanessa Polito·Paola Testa·Bart De Pontieu·Sergey A. Belov
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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.

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Alexander J. B. Russell, Vanessa Polito, Paola Testa, Bart De Pontieu, Sergey A. Belov. 2025-09-01. Solar Flare Ion Temperatures. https://doi.org/10.3847/2041-8213%2Fadf74a

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