TEC prediction performance of the IRI-2012 model over Ethiopia during the rising phase of solar cycle 24 (2009–2011)

This paper discusses the performance of the latest version of the International Reference Ionosphere (IRI-2012) model for estimating the vertical total electron content (VTEC) variation over Ethiopian regions during the rising phase of solar cycle 24 (2009–2011). Ground-based Global Positioning System (GPS) VTEC data, inferred from dual-frequency GPS receivers installed at Bahir Dar (geographic latitude 11.6°N and longitude 37.35°E, geomagnetic latitude 2.64°N and longitude 108.94°E), Nazret (geographic latitude 8.57°N and longitude 39.29°E, geomagnetic latitude −0.25°N and longitude 111.01°E), and Robe (geographic latitude 7.11°N and longitude 40.03°E, geomagnetic latitude −1.69°N and longitude 111.78°E), are compared to diurnal, monthly, and seasonal VTEC variations obtained with the IRI-2012 model. It is shown that the variability of the diurnal VTEC is minimal at predawn hours (near 0300 UT, 0600 LT) and maximal between roughly 1000 and 1300 UT (1300–1600 LT) for both the experimental data and the model. Minimum seasonal VTEC values are observed for the June solstice during the period of 2009–2011. Moreover, it is shown that the model better estimates diurnal VTEC values just after the midnight hours (0000–0300 UT, 0300–0600 LT). The modeled monthly and seasonal VTEC values are larger than the corresponding measured values during the period of 2009–2010 when all options for the topside electron density are used. An important finding of this study is that the overestimation of VTEC values derived from the model decreases as the Sun transitions from very low to high solar activity. Moreover, it is generally better to use the model with the NeQuick option for the topside electron density when estimating diurnal, monthly, and seasonal VTEC variations.