Performance Analysis of Ionospheric TECmodelsoverthe Africanregion during the geomagnetic storm of March 2015

Abstract This paper investigates the diurnal variations of modelled and observed Vertical Total Electron Content (VTEC) over the African region (40oN to + 40oS, 25oW to 65oE) obtained from ground-based Global Navigation Satellite System (GNSS) receivers. The investigations on ionospheric response during the super geomagnetic storm time (17 March 2015) is very crucial, especially over African low latitudes. Hence, the performance of ionospheric models has been evaluated in this paper. The VTEC predictability by regional/global ionospheric models (AfriTEC, IRI-2016, IRI-Plas 2017, GIM-CODE and Nequick-G) is evaluated by using root mean square error (RMSE) method and percentage deviation by comparing the GPS/GNSS-VTEC obtained from 10 IGS (International GNSS Service) stations with the modelled-VTEC values over African region. It is observed that peculiarity in VTEC values is evident during the superstorm sudden commencement when compared to the pre and post-storm periods. Northern hemisphere stations data showed/revealed a twin peak in the diurnal VTEC patterns. The enhanced VTEC values were observed over all the 10 IGS stations on the storm day than on other quiet days. Moreover, during the post-storm days (18–20 March 2015), these VTEC values decreased more than on quiet days over the IGS stations in southern hemisphere (MBAR, MAYG, HARB, SBOK). On the other hand, during the post-storm days (18–20 March 2015), the VTEC values remained high over the geomagnetic northern hemisphere (NOT1, SFER, MAS1, CPVG, NKLG). It is worth mentioning that three northern IGS stations (NOT1, SFER and MAS1) displayed a VTEC increase record of approximately 75–90%, which is due to the extension of Equatorial Ionization Anomaly (EIA) during the geomagnetic storm whereas the other northern stations at EIA trough region (CPVG, BJCO, NKLG) registered a VTEC increment of 7%, 26% and 25% respectively. Southern IGS stations registered an enhancement in VTEC of about 5%. The VTEC maps from AfriTEC, IRI-2016 and Nequick-G were able to predict the feature of Equatorial Ionospheric Anomaly (EIA) at around 200N/150S. The GPS-VTEC values at IGS stations located on the geomagnetic EIA crests (in both northern and southern hemispheres) and in the trough (equatorial stations) are higher than those of the IGS stations situated at midlatitudes. AfriTEC, which is a regional model, recorded lowest RMSE values over all the stations. The prediction results show that the regional model performance is better than the global ionospheric models (IRI-2016 and Nequick-G models) especially over EIA latitudes of African region.