Global Ionospheric F Region Parameters From GNSS-POD Limb Measurements: Evaluations and Comparisons With Two Empirical Models - IRI-2020 and NeQuick-2
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Swarnalingam, Nimalan, Dong L. Wu, Dieter Bilitza, Daniel J. Emmons, Cornelius Csar Jude H. Salinas, Artem Smirnov, and Yenca Migoya-Orue. “Global Ionospheric F Region Parameters From GNSS-POD Limb Measurements: Evaluations and Comparisons With Two Empirical Models - IRI-2020 and NeQuick-2.” Journal of Geophysical Research: Space Physics 130, no. 4 (April 2025): e2024JA033466. https://doi.org/10.1029/2024JA033466.
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
An optimal estimation (OE) technique has recently been developed for F region electron density (Ne) using Global Navigation Satellite System (GNSS) limb sounding on low Earth orbit (LEO) satellites (COSMIC-2, Spire, and FengYun-3). This method provides unprecedented spatiotemporal sampling for global monthly Ne climatology within 100–500 km in 2 hr intervals. The global dataset, collected during mid to moderately high solar activity, is compared with leading models: IRI-2020 and NeQuick-2. Diurnal variations in summer, winter, and equinoctial months are examined for the F2-layer peak, as well as the topside and bottomside of the F region. The observed and modeled NmF2 and hmF2 show good agreement during the daytime, but discrepancies appear with NeQuick-2 at night. The OE-retrieved dataset reveals distinct interhemispheric differences in topside scale height between the summer and winter hemispheres, which are not adequately captured by models. The estimated topside scale heights in IRI-2020 are ~20–30 km higher than observations on regional scale, but this difference decreases to ~12–20 km on global scale. In the bottomside, the agreement between observations and models varies significantly between daytime and nighttime conditions. During the daytime, the global bottomside thicknesses derived from OE-retrieved profiles agree within 10 km with the IRI-2020, but they are ~10–15 km higher than NeQuick-2. The nighttime thicknesses differ substantially, with deviations reaching up to ~30 km compared to IRI-2020 and ~45 km compared to NeQuick2. As models face challenges due to lack of reliable measurements, especially in the topside and bottomside, improvements in GNSS-LEO observing techniques can provide more accurate and comprehensive data to characterize the global ionosphere.