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Abstract We present an analysis of helium ion (He+) fraction in an altitude range from about 400 km to around 700 km and its relationship to the ion temperature (Ti) and the vertical ion drift under solar maximum conditions. The data were obtained from the Arecibo incoherent scatter radar during 27 September to 1 October 2014 and 16–20 December 2014. The large He+fraction (>10%) lasts 15 hr per day during the winter solstice, which is 3 times larger than during fall equinox. This difference is caused by the more persistent downward ion drift in the winter. The incremental He+fraction and incrementalTiare well anticorrelated, and the anticorrelation is more prominent during the daytime. These characteristics are associated with whether O+and He+are in diffusive equilibrium. During nighttime, we show that the vertical ion flow is downward causing the He+layer peak altitude to move to an altitude of 500 km from above 650 km. According to our analysis, He+fraction has to be larger than two thirds for diffusive equilibrium to occur above the He+peak height. Therefore, above the He+peak altitude, O+and He+cannot be in diffusive equilibrium with He+being the minor species. The vertical ion flow plays an important role in determining the diurnal variation and seasonal difference of He+distribution and whether He+is in a diffusive equilibrium with O+.
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This content will become publicly available on November 11, 2025
Measurements of F 1 ‐ Region Ionosphere State Variables at Arecibo Through Quasi Height‐Independent Exhaustive Fittings of the Incoherent Scatter Ion‐Line Spectra
Abstract We discuss an exhaustive search approach to fit the incoherent scatter spectrum (ISS) in the F1‐region for molecular ion fraction (fm), ion temperature (Ti), and electron temperature (Te). The commonly used “full profile” approach for F1‐region measurements parameterizes the molecular ion fraction as a function of altitude and fits all the related heights for the state variables. In our approach, we fit the ISS at each height forfm,Ti,Te, and ion velocity (Vi) independently. Our exhaustive search method finds all the major local minima at each altitude. Although a parameterized function is used to guide the algorithm in finding the best solution, the fitting parameters retain their local characteristics. Despite that fittingfm,Ti, andTewithout constraints requires Doppler shift to be accurately determined and the ISS signal‐to‐noise ratio higher than the full‐profile method, simulations show thatTi,Te, andfmcan be recovered within a few percent accuracy with a moderate signal‐to‐noise ratio. We apply the exhaustive search approach to the Arecibo high‐resolution incoherent scatter radar data taken on 13 September 2014. The derived ion and electron temperatures are sensitive enough to reveal thermosphere gravity waves commonly seen in the electron density previously. Our method is more robust than previous height‐independent fitting methods. Comparison with another Arecibo program indicates our results are likely more accurate. Simultaneous high‐resolution measurements ofTi,Te,fm,Vi, and electron concentration (Ne) in our approach open new opportunities for synergistic studies of the F1‐region dynamics and chemistry.
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- Award ID(s):
- 2152109
- PAR ID:
- 10557814
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 129
- Issue:
- 11
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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