| Autor: |
Cantrall, C. E.1 (AUTHOR) clayton.cantrall@jhuapl.edu, Mrak, S.1 (AUTHOR), Paxton, L. J.1 (AUTHOR), Zhang, Y.1 (AUTHOR), Nikoukar, R.1 (AUTHOR), Schaefer, R. K.1 (AUTHOR), Yee, J. H.1 (AUTHOR) |
| Předmět: |
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| Zdroj: |
Journal of Geophysical Research. Space Physics. Jul2024, Vol. 129 Issue 7, p1-8. 8p. |
| Abstrakt: |
Two solar eclipse events in 2023 appeared to produce considerable enhancements in the thermospheric column density ratio of monatomic oxygen to molecular nitrogen (ΣO/N2) as measured by TIMED GUVI. We quantify potential sources for eclipse‐induced ΣO/N2 changes and find that the observed enhancements arise from the ionospheric O+ radiative recombination contribution to the OI 135.6 nm emission from which ΣO/N2 is derived. Variations in the solar Extreme Ultra Violet (EUV) and X‐ray spectrum, due to the difference between the disk spectrum and the coronal spectrum, are also considered but shown to have negligible contributions to the ΣO/N2 enhancements. After accounting for the radiative recombination contribution, we constrain the real thermospheric compositional change to the uncertainty level of the measurements of 5%–10%. These results are valuable for the interpretation of eclipse‐induced ΣO/N2 changes that will further first‐principle model comparisons and lead to a better understanding of the response of the thermosphere to localized variations in solar EUV and X‐ray forcing. Plain Language Summary: The Thermosphere Ionosphere Mesosphere Energetics and Dynamics' Global Ultraviolet Imager provides an estimate of the column ratio of monatomic oxygen (O) to molecular nitrogen (N2) in the upper atmosphere (ΣO/N2) as a data product under normal, sunlit conditions. Eclipses are special conditions. In this paper, we model the measured ultraviolet emissions from O and N2 that go into the retrieval algorithm to understand why this increase in the radiance ratio occurs within the totality of the eclipse. There are two components to the O emission, the glow created by electrons (photoelectrons) that result from the ionization of the upper atmosphere and the glow created by recombination of ionospheric O+ ions. We find that the photoelectron source decreases significantly during the eclipse, but near the magnetic equator, the ionospheric recombination emission does not, which causes the retrieval algorithm to overestimate the ΣO/N2 column density ratio during eclipses. The observations and models are consistent with this explanation. Key Points: The apparent thermospheric ΣO/N2 enhancements (10%–30%) for two eclipse events are found to be predominantly of ionospheric originVariations in the solar spectrum due to wavelength‐dependent attenuation are found to have a negligible impact on ΣO/N2 during the eclipseThe true eclipsed‐induced thermosphere compositional changes are determined to be within 5%–10% of the pre‐eclipse values [ABSTRACT FROM AUTHOR] |
| Databáze: |
GreenFILE |
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