Improved models for estimating sporadic-E intensity from GNSS radio occultation measurements

Abstract

Several models for estimating sporadic-E intensity from Global Navigation Satellite System (GNSS) radio occultation (RO) observation have previously been developed using a single perturbation or intensity parameter, such as phase-based total electron content (TEC) or the amplitude-based S4 index. Here, we outline two new models that use a combination of phase and amplitude parameters for the L1 and L2 signals. These models show a significant improvement over the baseline models used for comparison. Furthermore, the GNSS-RO parameters are compared with several different ionosonde intensity parameters including the direct foEs and fbEs measurements along with the metallic-ion based foμEs and fbμEs parameters which account for the background E-region density. Interestingly, the phase-based σϕ scintillation index shows the strongest correlation to foEs and fbEs while amplitude-based S4 shows the strongest correlation to foμEs and fbμEs. While the metallic-ion based foμEs and fbμEs parameters are physically ideal for GNSS-RO observations, we show difficulties in practical implementation due to the reliance on a background E-region density estimate using a model such as the International Reference Ionosphere (IRI). Ultimately, we provide two improved sporadic-E intensity models that can be used for future GNSS-RO based studies along with a recommendation to compare against the ionosonde-based foEs parameter.

A Simplified Method of True Height Analysis to Estimate the Real Height of Sporadic E Layers

“…In principle, this could reduce the inaccuracies caused by the empirically modeled IRI profiles. However, in making this proposition, it is recognized that the ionogram-inverted E region N e (h) profiles have their own inaccuracies and uncertainties which at times can be quite high, as was pointed out in a recent paper by Emmons et al (2023). It should be added here that the reliability and appropriateness of the ambient E region electron density profile, which is needed in obtaining the true height of sporadic E, is an issue that requires further consideration and study.…”

“…In this work, where the sporadic E blanketing frequency fbEs was used instead of foEs, the authors provided only a few details and no information as how the real heights affected their findings relative to the measured virtual heights and the corresponding blanketing frequencies. The Gooch et al (2020) Es true height analysis method was also employed in a recent paper by Emmons et al (2023) that tested several approaches used to estimate sporadic E intensities in GPS satellite radio occultation studies.…”

“…The use of h′Es instead of hEs has been applied in many sporadic E studies. Among others, these include: (a) several Es diurnal and seasonal variability investigations (e.g., see a recent paper by Haldoupis et al (2023) and more references therein), (b) "Height Time Intensity" (HTI) studies of tidal periodicities and altitude descent of sporadic E layers (e.g., see Haldoupis et al, 2006; and a review paper by Haldoupis (2012)), (c) comparison studies of Es altitudes measured independently by satellite GPS (Global Positioning System) radio occultation (RO) methods and ionosondes (e.g., see Arras, 2010;Ellis et al, 2024;Gan et al, 2022;Resende et al, 2018;Sobhkhiz-Miandehi et al, 2023, and several more references), and (d) the computation of foμEs, which is an ionogram-based parameter for measuring Es metal ion densities and thus the associated layer intensities (Ellis et al, 2024;Emmons et al, 2023;Haldoupis, 2019;Haldoupis et al, 2020). Therefore, the convenient adoption of hEs being equal to h′Es should have caused inaccuracies in past studies.…”