Modeling the occurrence probability of sporadic-E based on GNSS radio occultation data

Sporadic E (Es) layers are a well-known ionospheric phenomenon, whose occurrence can cause anomalous propagation of radio waves utilized for communication and broadcast. Es layers are very thin layers of metallic ions such as Fe+, Mg+, and Ca+ formed  mainly by atmospheric tidal wind shears.  Their peak density exceeds the E-layer peak density and can even exceed the F-layer peak density. Because of their effect on radio waves a user needs to know when there is a high probability of Es occurrence. It is the goal of this study to develop a global model of Es occurrence probability and to make it publicly available through inclusion in the International Reference Ionosphere (IRI). We use Es data obtained by Arras et al. (2022) from GNSS radio occultation observations from various satellites (CHAMP, Spire, KOMPSAT-5, COSMIC1 & 2, TANDEM-X, and TerraSAR-X) for the time period 2001-2022. We will briefly discuss the variation of the Es occurrence rate with latitude, longitude, local time, season, solar activity, and magnetic activity. as observed with this data base. We found that the strongest dependencies are with local time, latitude and season, while weaker ones exist with longitude and solar activity. We use spherical harmonics to describe the global expansion of the strongest influences establishing a core model. Second order influences, e.g., solar activity variations, are modelled as a perturbation on the core model. First results obtained with the new model will be presented. References Arras, C., Resende, L.C.A., Kepkar, A. et al. Sporadic E layer characteristics at equatorial latitudes as observed by GNSS radio occultation measurements. Earth Planets Space 74, 163 (2022). https://doi.org/10.1186/s40623-022-01718-y