This work examines the performance of four ionospheric models for estimating Total Electron Content (TEC) over Nigeria.The observed Vertical TEC values retrieved from five GPS stations located between geographic latitudes 4.80° and 12.47°N were analyzed and compared with corresponding values obtained from the International Reference Ionosphere (IRI-01corrected option), the IRI-Plasmasphere 2017, NeQuick-2 and Nigerian Total Electron Content (NIGTEC) models.NIGTEC model used in this work is a neural network based model developed at the Nigerian Centre for Atmospheric Research as a regional model, while the IRI-01cor, IRI-Plas 2017 and NeQuick are well-known global ionospheric models.We evaluated TEC from the four models at hourly levels for all the days of the year 2012 (sunspot number Rz = 84.4).TEC directly derived from the five GPS stations under consideration was also evaluated for all the days of the year.The paper also considered the performance of the models under geomagnetically quiet condition (Ap ≤ 5).The NIGTEC model has shown better agreement with the observed VTEC when compared with the IRI-01cor, NEQUICK and IRI-Plas 2017 models especially during the pre-Sunrise period.With mean values of RMSE as 3.378 TECU and 3.8403 TECU for all days and geomagnetically quiet condition respectively, NIGTEC returned the lowest RMSE values at all conditions.The modelled TEC obtained from all the four models, at both geomagnetically disturbed and quiet times, follow the diurnal pattern of the observed GPS-TEC with variations in magnitudes.The NIGTEC model performed better than IRI-01cor, NEQUICK and IRI-Plas 2017 even when only geomagnetically quiet condition was considered.The NeQuick and NIGTEC model correctly captured the annual distribution pattern of the observed GPS-TEC across the stations.This distribution was over-smoothed by the IRI and IRI-Plas models.
This work examines the performance of four ionospheric models for estimating Total Electron Content (TEC) over Nigeria.The observed Vertical TEC values retrieved from five GPS stations located between geographic latitudes 4.80° and 12.47°N were analyzed and compared with corresponding values obtained from the International Reference Ionosphere (IRI-01corrected option), the IRI-Plasmasphere 2017, NeQuick-2 and Nigerian Total Electron Content (NIGTEC) models.NIGTEC model used in this work is a neural network based model developed at the Nigerian Centre for Atmospheric Research as a regional model, while the IRI-01cor, IRI-Plas 2017 and NeQuick are well-known global ionospheric models.We evaluated TEC from the four models at hourly levels for all the days of the year 2012 (sunspot number Rz = 84.4).TEC directly derived from the five GPS stations under consideration was also evaluated for all the days of the year.The paper also considered the performance of the models under geomagnetically quiet condition (Ap ≤ 5).The NIGTEC model has shown better agreement with the observed VTEC when compared with the IRI-01cor, NEQUICK and IRI-Plas 2017 models especially during the pre-Sunrise period.With mean values of RMSE as 3.378 TECU and 3.8403 TECU for all days and geomagnetically quiet condition respectively, NIGTEC returned the lowest RMSE values at all conditions.The modelled TEC obtained from all the four models, at both geomagnetically disturbed and quiet times, follow the diurnal pattern of the observed GPS-TEC with variations in magnitudes.The NIGTEC model performed better than IRI-01cor, NEQUICK and IRI-Plas 2017 even when only geomagnetically quiet condition was considered.The NeQuick and NIGTEC model correctly captured the annual distribution pattern of the observed GPS-TEC across the stations.This distribution was over-smoothed by the IRI and IRI-Plas models.
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