Strong Photospheric Heating Indicated by Fe I 6173 Å Line Emission During White-Light Solar Flares

Between 2017 and 2024, the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory has observed several white-light solar flares. Notably, for the X9.3 flare of September 6, 2017, HMI spectro-polarimetric observations reveal one or more locations within the umbra of the associa...

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Bibliographic Details
Published inarXiv.org
Main Authors Granovsky, Samuel, Kosovichev, Alexander G, Sadykov, Viacheslav M, Kerr, Graham S, Allred, Joel C
Format Paper
LanguageEnglish
Published Ithaca Cornell University Library, arXiv.org 09.10.2024
Subjects
Chromosphere
Emission
Heating
Photosphere
Polarimetry
Satellite observation
Soft x rays
Solar activity
Solar flares
Solar observatories
White light
Wind spacecraft
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Summary:Between 2017 and 2024, the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory has observed several white-light solar flares. Notably, for the X9.3 flare of September 6, 2017, HMI spectro-polarimetric observations reveal one or more locations within the umbra of the associated active region where the Fe I 6173 Å line goes into full emission, indicating significant heating of the photosphere and lower chromosphere. For these flares, we performed a spectro-polarimetric analysis at the aforementioned locations using HMI 90s cadence Stokes data. At the Fe I emission locations, line-core emission is observed to last for a single 90 s frame and is either concurrent with or followed by increases in the line continuum intensity lasting 90 to 180 seconds. This is followed by a smooth decay to pre-flare conditions over the next three to twenty minutes. For most locations, permanent changes to the Stokes Q, U, and/or V profiles were observed, indicating long-lasting non-transient changes to the photospheric magnetic field. These emissions coincided with local maxima in hard X-ray emission observed by the Konus instrument onboard the Wind spacecraft, as well as local maxima in the time derivative of soft X-ray emission observed by GOES satellites. Comparison of the Fe I 6173 Å line profile synthesis for the ad-hoc heating of the initial empirical VAL-S umbra model and quiescent Sun (VAL-C-like) model indicates that the Fe I 6173 Å line emission in the white-light flare kernels could be explained by the strong heating of initially cool photospheric regions.
ISSN:2331-8422