Variability of TEC and improvement of performance of the IRI model over Ethiopia during the high solar activity phase

Abstract. This paper discusses the monthly and seasonal variation of the total electron content (TEC) and the improvement of performance of the IRI model in estimating TEC over Ethiopia during the solar maximum (2013–2016) phase employing GPS TEC data inferred from the GPS receivers installed at different regions of Ethiopia. The results reveal that both the measured and modeled seasonal diurnal VTEC values start increasing at 03:00 UT (06:00 LT) and attain their peak values (mostly in the time interval of 09:00–13:00 UT or 12:00–16:00 LT). Moreover, both the arithmetic mean measured and modeled VTEC values, generally, show maximum and minimum values in the equinoctial and June solstice months, respectively. The results also show that, even though overestimation of the modeled VTEC has been observed on most of the hours, the model is generally good to estimate both the monthly and seasonal diurnal hourly VTEC values, especially in the early morning hours (00:00–03:00 UT or 03:00–06:00 LT). Moreover, the overall results show that using NeQuick option for the topside electron density is the best option in estimating the TEC variation. It has also been shown that the model does not show a good improvement on its performance in estimating both the monthly and seasonal hourly and arithmetic mean VTEC values. Moreover, the model does not respond to the effects resulting from storm.