Performance of International Reference Ionosphere-2016 and NeQuick-2 Models in Estimating Global Positioning System Total Electron Content Over a Nigerian Equatorial Station during Two Phases of Solar Cycle 24
Eugene O. Onori *
Department of Physics, Lagos State University, Ojo, Lagos, Nigeria.
Aghogho Ogwala
Department of Physics, Eko University of Medicine and Health Sciences, Ijanikin, Lagos, Nigeria.
Alimat A. Asalu
Department of Physics, Lagos State University, Ojo, Lagos, Nigeria.
James M. Whetode
Department of Physics, Lagos State University, Ojo, Lagos, Nigeria.
Muyiwa K. Bamgbose
Department of Physics, Lagos State University, Ojo, Lagos, Nigeria.
Yusuf O. Kayode
Department of Physics, Lagos State University of Education, Ijanikin, Lagos, Nigeria.
Abiola S. Ogungbe
Department of Physics, Lagos State University, Ojo, Lagos, Nigeria.
Emmanuel O. Somoye
Department of Physics, Lagos State University, Ojo, Lagos, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Aim: This study examines the temporal behaviour of GPS-derived total electron content (GPS-TEC) and evaluates the capability of the International Reference Ionosphere-2016 (IRI-2016) and NeQuick-2 models to reproduce observed ionospheric conditions over Birnin Kebbi, Nigeria (12.64° N, 4.22° E; dip latitude 2.68° N).
Methods: The analysis considers 2011 and 2014, representing the ascending and maximum phases of Solar Cycle 24, respectively. Dual-frequency GNSS observations were processed to vertical TEC (VTEC), and corresponding model estimates were obtained from IRI-2016 and NeQuick-2. Monthly mean diurnal data were grouped into four seasons: March equinox, June solstice, September equinox and December solstice. Model disagreement was quantified using mean absolute error (MAE).
Results: GPS-TEC increased from pre-sunrise values to daytime maxima and decreased after sunset. Observed maxima generally occurred at 13:00–15:00 LT and had a dome-shaped profile, whereas the models frequently produced an earlier maximum and a noon-depression or double-peaked structure. June-solstice TEC was consistently lower than the other seasonal groupings. IRI-2016 had the lower MAE in most seasonal comparisons; NeQuick-2 showed a slightly lower MAE only during the December solstice of 2011.
Conclusion: IRI-2016 provided the closer climatological representation for most of the cases examined, but neither model reproduced all features of the observed local-time and seasonal behaviour. The findings support the need for regional validation of empirical ionospheric models over the Nigerian equatorial sector.
Keywords: GPS-TEC, vertical total electron content, IRI-2016, NeQuick-2, equatorial ionosphere, Solar Cycle 24