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. We investigated total electron content (TEC) at Ilorin (8.50∘ N4.65∘ E, dip lat. 2.95) for the year 2010, a year of low solaractivity in 2010 with Rz=15.8. The investigation involved the use of TECderived from GPS, estimated TEC from digisonde portable sounder data (DPS),and the International Reference Ionosphere (IRI) and NeQuick 2 (NeQ) models.During the sunrise period, we found that the rate of increase in DPS TEC, IRITEC, and NeQ TEC was higher compared with GPS TEC. One reason for this can beattributed to an overestimation of plasmaspheric electron content (PEC)contribution in modeled TEC and DPS TEC. A correction factor around thesunrise, where our finding showed a significant percentage deviation betweenthe modeled TEC and GPS TEC, will correct the differences. Our findingrevealed that during the daytime when PEC contribution is known to be absentor insignificant, GPS TEC and DPS TEC in April, September, and Decemberpredict TEC very well. The lowest discrepancies were observed in May, June,and July (June solstice) between the observed values and all the model valuesat all hours. There is an overestimation in DPS TEC that could be due toextrapolation error while integrating from the peak electron density of F2(NmF2) to around ∼1000 km in the Ne profile. Theunderestimation observed in NeQ TEC must have come from the inadequaterepresentation of contribution from PEC on the topside of the NeQ modelprofile, whereas the exaggeration of PEC contribution in IRI TEC amounts tooverestimation in GPS TEC. The excess bite-out observed in DPS TEC andmodeled TEC indicates over-prediction of the fountain effect in these models.Therefore, the daytime bite-out observed in these models requires a modifierthat could moderate the perceived fountain effect morphology in the modelsaccordingly. The daytime DPS TEC performs better than the daytime IRI TEC andNeQ TEC in all the months. However, the dusk period requires attention due tothe highest percentage deviation recorded, especially for the models, inMarch, November, and December. Seasonally, we found that all the TECsmaximize and minimize during the March equinox and June solstice,respectively. Therefore, GPS TEC and modeled TEC reveal the semiannualvariations in TEC.

Morphology of GPS and DPS TEC over an equatorial station: validation of IRI and NeQuick 2 models