Update of ICON-FUV hmF2 and NmF2 Comparison with External Radio Observations

Abstract

The Far Ultraviolet Imaging Spectrograph (FUV) onboard the NASA-ICON spacecraft has been providing nighttime O + density profiles over mid-and low-latitude since December 2019. These profiles are compared to electron density profiles provided by GNSS radiooccultations and ground-based ionosondes, mainly at the F-peak level where both density and height are compared. This work is an important update of the earlier study published by Wautelet et al. (J. Geophys. Res. Space Phys. 126(11):e2021JA029360, 2021) for two reasons: First, several methodological improvements have been implemented at the calibration and inversion levels. Second, the present work relies on an extended time range, ranging from December 2019 to August 2022, covering therefore periods of increased solar activity, which was not the case for the previous work. It is found that the peak density and height are, on average, similar to radio-based observations by about 10% in density and 7 km in height, meaning that FUV provides peak characteristics compatible with existing ionospheric datasets based on radio signals. However, comparisons of FUV and radio-occultation profiles have to be considered very carefully due to the potentially large difference in the observation geometry, which can account for large density discrepancies even between profiles being closely located and mostly simultaneous. This is particularly important around the crests of the equatorial anomaly where the largest density discrepancies have been observed. In addition, this study highlights the variability of the FUV profiles at the bottomside level, with the analysis of cases where rather large density values were observed while small density values are expected. The latter observation does nevertheless not impact the statis-The Ionospheric Connection Explorer (ICON) Mission: First Results Edited by David E. Siskind and Ruth S. Lieberman G. Wautelet

In Flight Performance of the Far Ultraviolet Instrument (FUV) on ICON

“…The authors conclude that FUV reliably monitors the peak density and height with an accuracy compatible to that of external data sources (Wautelet et al. 2023 ).…”

“…( 2021 ) were expanded and substantially enhanced (Wautelet et al. 2023 ). ICON FUV data between December 2019 and August 2022 with improved calibration and background subtraction, better star removal, and stronger data quality requirements, allowed for a direct comparison between NmF2 and hmF2 determinations by the three measurement methods.…”

Inferring the Ionospheric State With the Far Ultraviolet Imager on the Fengyun‐4C Geostationary Satellite: Retrieval Algorithm and Verification

“…This model has been verified by comparison with the more rigorous Monte Carlo radiative transfer model of Qin and Harding (2020) that uses an angle-dependent partial frequency redistribution function. Moreover, the model has been implemented for the inversion of the limb scans of the OI 135.6 nm emission from the Ionospheric Connection Explorer mission to derive the electron density profiles (Kamalabadi et al, 2018), which agree well with external radio measurements (Wautelet et al, 2023).…”

“…Specifically, the conjugate location of a specific GOLD observation is determined by using the International Geomagnetic Reference Field model (Alken et al, 2021). A GOLD observation is excluded if its conjugate location has a SZA less than 110° (Wautelet et al, 2023). In Figures 4a, 4d, and 4g, we compare the ionosonde n m F 2 measurements with the N max values taken directly from the GOLD v3 data product, which are retrieved using Equation 3 with H = 50 km.…”