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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 5 | Copyright
Ann. Geophys., 36, 1457-1469, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 24 Oct 2018

Regular paper | 24 Oct 2018

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

Olumide Olayinka Odeyemi1, Jacob Adeniyi2, Olushola Oladipo3, Olayinka Olawepo3, Isaac Adimula3, and Elijah Oyeyemi1 Olumide Olayinka Odeyemi et al.
  • 1Department of Physics, University of Lagos, Lagos, Nigeria
  • 2Department of Physical Sciences, Landmark University, Omu-Aran, Nigeria
  • 3Department of Physics, University of Ilorin, Ilorin, Nigeria

Abstract. We investigated total electron content (TEC) at Ilorin (8.50°N 4.65°E, dip lat. 2.95) for the year 2010, a year of low solar activity in 2010 with Rz = 15.8. The investigation involved the use of TEC derived 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, IRI TEC, and NeQ TEC was higher compared with GPS TEC. One reason for this can be attributed to an overestimation of plasmaspheric electron content (PEC) contribution in modeled TEC and DPS TEC. A correction factor around the sunrise, where our finding showed a significant percentage deviation between the modeled TEC and GPS TEC, will correct the differences. Our finding revealed that during the daytime when PEC contribution is known to be absent or insignificant, GPS TEC and DPS TEC in April, September, and December predict TEC very well. The lowest discrepancies were observed in May, June, and July (June solstice) between the observed values and all the model values at all hours. There is an overestimation in DPS TEC that could be due to extrapolation error while integrating from the peak electron density of F2 (NmF2) to around  ∼ 1000km in the Ne profile. The underestimation observed in NeQ TEC must have come from the inadequate representation of contribution from PEC on the topside of the NeQ model profile, whereas the exaggeration of PEC contribution in IRI TEC amounts to overestimation in GPS TEC. The excess bite-out observed in DPS TEC and modeled TEC indicates over-prediction of the fountain effect in these models. Therefore, the daytime bite-out observed in these models requires a modifier that could moderate the perceived fountain effect morphology in the models accordingly. The daytime DPS TEC performs better than the daytime IRI TEC and NeQ TEC in all the months. However, the dusk period requires attention due to the highest percentage deviation recorded, especially for the models, in March, November, and December. Seasonally, we found that all the TECs maximize and minimize during the March equinox and June solstice, respectively. Therefore, GPS TEC and modeled TEC reveal the semiannual variations in TEC.

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Short summary
This paper investigates the combined relationship between the GPS TEC and DPS TEC, and validations of IRI TEC and NeQ TEC models. Our findings reveal the suitability of DPS TEC, IRI TEC, and NeQ TEC in place of GPS TEC. The DPS TEC predicts GPS TEC very well during the daytime when PEC contribution is often negligible; however, the dusk period requires a substantial correction. Thus, the changed TEC obtained could be used to improve models for the equatorial station in Africa.
This paper investigates the combined relationship between the GPS TEC and DPS TEC, and...