Validation of the IRI-2020 model for the topside-plasmasphere using GNSS TEC measurements

Abstract

The 2020 update of the International Reference Ionosphere (IRI) model introduces a new topside option, COR2, for the formulation of its electron density profile, as well as two plasmaspheric extension options based on the GCPM model of Gallagher et al. (2000) and the IMAGE/RPI model of Ozhogin et al. (2012). We validate the COR2-Gallagher and COR2-Ozhogin topside-plasmasphere options of IRI-2020 using GNSS VTEC measurements and compare them to the NeQuick model used as the default option in IRI-2016. VTEC data from a total of 21 GNSS ground-based receivers are compared to predictions of the IRI model, ranging from low (< 30°) to middle (30°-60°) magnetic latitudes, during high (year 2014; F10.7$\sim$140 sfu) and low (year 2019; F10.7$\sim$70 sfu) solar activity. Peak plasma frequency (foF2) data from co-located digisondes are ingested into the model to ensure the relevance of the comparison. The three topside-plasmasphere options perform equally well at mid-latitudes (RMSE$\sim$3 TECU). At low latitudes, the NeQuick option (RMSE$\sim$9 TECU) performs better than both the COR2-Gallagher and COR2-Ozhogin options (RMSE > 10 TECU). For all options, the modeled VTEC is consistently overestimated during the autumn/winter daytime at mid-latitudes regardless of solar activity, and throughout the day at low latitudes during low solar activity.