Performance of NeQuick-2, IRI-Plas 2017 and GIM models over Ethiopia during varying solar activity periods

Abstract

This paper investigates the performance of NeQuick-2, the latest version of International Reference Ionosphere IRI extended to the Plasmasphere (IRI-Plas 2017), and Global Ionospheric Map (GIM) models over four stations deployed in Ethiopia during medium, high, and low solar activity periods. The monthly and seasonal mean diurnal variations of Vertical Total Electron Content (VTEC) derived from NeQuick-2, IRI-Plas 2017 and GIM models were compared with the GPS-VTEC values in terms of Root-Mean-Square Errors (RMSE) and correlation coefficients (r). It was found that the monthly and seasonal mean diurnal VTEC variations agree fairly well with the GPS-VTEC at all stations although with some offsets. For the entire years of the study, the highest monthly mean VTEC variation is observed during equinox months, whereas minimum in the solstice months. The NeQuick-2 model monthly and seasonal mean VTEC output were generally better than IRI-Plas 2017 and GIM models output in most of the stations during medium solar activity year of 2012. For all models, the significant discrepancy (i.e, overestimations or underestimations) is observed during daytimes and seasons of high solar activities. In some cases, the IRI-Plas 2017 model displayed poor performance during medium and low solar activity periods, while it showed a better agreement for some stations (e.g. asos, armi, and bdmt) during high solar activity phase (especially in March equinox and December solstice). The performance of GIM model was good for most of the stations during low-solar activity year of 2016 and during the study years for adis, while it has poor performance during the periods of high solar activity year of 2014. All models correlated well, although GIM model was highly correlated with the GPS-VTEC value (r ≥0.99). The IRI-Plas 2017 model correlated better with the GPS-VTEC than NeQuick-2 model during the study years. Moreover, the performance of IRI-Plas 2017 model was better during high than low and medium periods of solar activity years. The GIM model has better performance for most stations (e.g. adis, asos, and bdmt) over the study region during low-solar activity period.