Validating the International Reference Ionosphere model through altimeter-satellite vTEC observations: implications for the topside ionosphere modeling

Abstract

In this paper, we evaluate the performance of the last version of the International Reference Ionosphere model (IRI-2020) in describing the vertical total electron content (vTEC) through a comparison against observations by several altimeter satellites (TOPEX/POSEIDON, JASON 1, 2, and 3) over the oceans. vTEC from these altimeter satellites cover the range from ground to about 1340 km of altitude, thus representing the contribution from the bottomside and topside ionosphere, and from the very first part of the plasmasphere.We focused on altimeter observations covering the last two solar cycles (years 2000–2022) which allowed testing the IRI performance on a global scale under different solar activity, local time, and seasonal conditions. The newly introduced IRI topside option (COR2) has also been compared with the one based on the NeQuick topside model, which was the previous IRI default option. This analysis evidenced how, on average, IRI-2020, with both topside models, provides an accurate description of altimeter vTEC with mean residuals below 1 TECu and standard deviation around 7 TECu. Both models show the best performance for vTEC values below about 30 TECu, while they both underestimate for muchhigher vTEC, particularly the NeQuick option. Performance of IRI-2020 is sensibly dependent on magnetic latitude, local time and season. The equatorial ionization anomaly, the sunrise sector at the geomagnetic equator, and the winter season at mid latitudes, particularly challenge the model.