Abstract This Letter proposes that the ion temperature is several times the local electron temperature in the hot onset phase and in the above-the-loop region of solar flares. The Letter considers: the evidence of spectral line Doppler widths (“nonthermal” 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.
Russell et al. (Wed,) studied this question.