TEC prediction performance of IRI-2012 model during a very low and a high solar activity phase over equatorial regions, Uganda

This paper examines the capacity of the latest version of the International Reference Ionosphere (IRI-2012) model in predicting the vertical total electron content (VTEC) variation over Uganda during a very low solar activity phase (2009) and a high solar activity (2012) phase. This has been carried out by comparing the ground-based Global Positioning System (GPS) VTEC inferred from dual-frequency GPS receivers installed at Entebbe (geographic latitude 0.038 degrees N and longitude 32.44 degrees E; geomagnetic latitude -9.53 degrees N and longitude 104.06 degrees E) and Mbarara (geographic latitude -0.60 degrees N and longitude 30.74 degrees E; geomagnetic latitude -10.02 degrees N and longitude 102.36 degrees E). In this work, the diurnal, monthly, and seasonal variations in the measured VTEC have been analyzed and compared with the VTEC derived from IRI-2012 model. It has been shown that the lowest diurnal peak GPS-VTEC values are observed in the June solstice months during both the low and the high solar activity phases. Similarly, the highest diurnal peak IRI-2012 VTEC values are observed in equinoctial months during both phases. The variability of the VTEC in both the experimental and model is minimal nearly at 03:00 UT (06:00 LT) and maximal mostly between 10:00 and 13:00 UT (13:00-16:00 LT) during both phases. The diurnal highest peak modeled VTEC value observed during the high solar activity phase is almost twice larger than the diurnal highest peak modeled VTEC value depicted during the low solar activity phase. Moreover, the highest monthly mean hourly measured VTEC value observed in October during the high solar activity phase is larger by more than twice the corresponding highest monthly mean hourly measured VTEC value observed in November during the low solar activity phase. Similarly, the lowest monthly measured VTEC value observed in July during the high solar activity phase is larger by more than twice the corresponding lowest measured monthly VTEC value observed in the same month during the low solar activity phase. It has also been shown that the highest measured seasonal mean hourly VTEC values are observed in the December solstice and the March equinox, respectively, during the low and the high solar activity phases, while the corresponding lowest measured VTEC values are observed in the June solstice during both phases. The model prediction generally follows the monthly and seasonal variations of measured VTEC, with the highest and the lowest monthly values being observed in equinoctial and solstice months, respectively, during both phases. The overall results show that the modeled diurnal, monthly, and seasonal VTEC values are generally larger than those corresponding measured VTEC values observed during both the low and the high solar activity phases, with the largest deviations being observed during the low solar activity phase. Moreover, the model does not respond to the effects resulting from the storm. Hence, unlike the measured VTEC values, the modeled VTEC values are unaffected by the storm.