Solar flare ion temperatures

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

doi:10.3847/2041-8213/adf74a

Solar flare ion temperatures

Alexander J. B. Russell^*, Vanessa Polito, Paola Testa, Bart De Pontieu, Sergey A. Belov

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

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.

Original language	English
Article number	L39
Number of pages	6
Journal	Astrophysical Journal Letters
Volume	990
Issue number	2
Early online date	3 Sept 2025
DOIs	https://doi.org/10.3847/2041-8213/adf74a
Publication status	Published - 10 Sept 2025

Keywords

Solar flare spectra
Solar flares
Stellar flares
Solar magnetic reconnection
Spectroscopy

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Cite this

@article{a269a6bc0fd941ec8fb5e113c9a32501,

title = "Solar flare ion temperatures",

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{\textquoteright}s magnetopause, Earth{\textquoteright}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.",

keywords = "Solar flare spectra, Solar flares, Stellar flares, Solar magnetic reconnection, Spectroscopy",

author = "Russell, \{Alexander J. B.\} and Vanessa Polito and Paola Testa and \{De Pontieu\}, Bart and Belov, \{Sergey A.\}",

note = "Funding: A.J.B.R. acknowledges support from STFC grant ST/W001195/1. V.P., P.T., and A.J.B.R. acknowledge NASA HGI grant No. 80NSSC20K0716. B.D.P., V.P., and P.T. were supported by NASA contract 80GSFC21C0011 (MUSE). P.T. was supported by contracts 4105785828 (MUSE), 8100002705 (IRIS), and NASA contract NNM07AB07C (Hinode/XRT) to the Smithsonian Astrophysical Observatory, and by NASA grant 80NSSC21K1684. S.A.B. acknowledges funding by STFC Grant ST/X000915/1.",

year = "2025",

month = sep,

day = "10",

doi = "10.3847/2041-8213/adf74a",

language = "English",

volume = "990",

journal = "Astrophysical Journal Letters",

issn = "2041-8205",

publisher = "American Astronomical Society",

number = "2",

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TY - JOUR

T1 - Solar flare ion temperatures

AU - Russell, Alexander J. B.

AU - Polito, Vanessa

AU - Testa, Paola

AU - De Pontieu, Bart

AU - Belov, Sergey A.

N1 - Funding: A.J.B.R. acknowledges support from STFC grant ST/W001195/1. V.P., P.T., and A.J.B.R. acknowledge NASA HGI grant No. 80NSSC20K0716. B.D.P., V.P., and P.T. were supported by NASA contract 80GSFC21C0011 (MUSE). P.T. was supported by contracts 4105785828 (MUSE), 8100002705 (IRIS), and NASA contract NNM07AB07C (Hinode/XRT) to the Smithsonian Astrophysical Observatory, and by NASA grant 80NSSC21K1684. S.A.B. acknowledges funding by STFC Grant ST/X000915/1.

PY - 2025/9/10

Y1 - 2025/9/10

N2 - 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.

AB - 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.

KW - Solar flare spectra

KW - Solar flares

KW - Stellar flares

KW - Solar magnetic reconnection

KW - Spectroscopy

UR - https://www.scopus.com/pages/publications/105015088491

U2 - 10.3847/2041-8213/adf74a

DO - 10.3847/2041-8213/adf74a

M3 - Article

SN - 2041-8205

VL - 990

JO - Astrophysical Journal Letters

JF - Astrophysical Journal Letters

IS - 2

M1 - L39

ER -

Solar flare ion temperatures

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Solar and Magnetospheric Plasmas: Solar and Magnetospheric Plasmas: Theory and Application

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Solar flare ion temperatures

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Solar and Magnetospheric Plasmas: Solar and Magnetospheric Plasmas: Theory and Application

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