Abstract
This paper carries out a comparative investigation of the Total Electron Content (TEC) values calculated by using the NeQuick-2 and IRI-Plas 2017 models. The investigation was carried out for the solar maximum year of 2013–2014 with data from eight GPS stations within the equatorial and low latitude regions. The results show that both models agree quite well with the observed TEC values obtained from GPS measurements in all the stations, although with some overestimations and underestimations observed during the daytime and nighttime hours. The NeQuick-2 model, in general, performed better in months, seasons, and in most of the stations when the IRI-Plas overestimates the GPS-TEC. However, it is interesting to know that with an increase in solar activity in some seasons, the quality of forecasting IRI-Plas can improve, whereas for the NeQuick-2 model, it decreases, but this is not true for all the seasons and all the stations. Factors causing the discrepancies in the IRI-Plas data model might be caused by the plasmaspheric part included in the IRI, and it is found to be maximum at the MBAR (34%) station, whereas that of the NeQuick-2 data model is found to be maximum at the ADIS (47.7%) station. There is a latitudinal dependence for both models in which the prediction error decreases with the increasing latitudes.
Highlights
The variation of the Earth’s ionosphere is complicated and may behave differently from region to region
NeQuick-2 monthly GPS-Total Electron Content (TEC) values were obtained using the Windows executable program created from the FORTRAN source code which was obtained from the Ionospheric Radio Propagation unit of the T/ICT4D laboratory (https://t-ict4d.ictp.it/nequick2/source-code), whereas the monthly Vertical Total Electron Content (VTEC) values of International Reference Ionosphere (IRI)-Plas 2017 were obtained using the Windows executable program which was obtained from the website of the IZMIRAN Institute (http://ftp.izmiran.ru/pub/izmiran/SPIM/)
The annual mean %Root Mean Square Deviation (RMSD) in the IRI-Plas model in stations within the equatorial region is at maximum at MBAR station (34%) during the year 2013 and decreases continuously from 34% to 32% as it moves towards a high solar activity year 2014, whereas in the stations outside the equation region, the annual mean %RMSD of the NeQuick-2 model decreases with increase in latitudes, except in ADIS when the RMSD value is 47.7% in the year 2014
Summary
The variation of the Earth’s ionosphere is complicated and may behave differently from region to region. Adebiyi et al [19,20] carried out an assessment of IRI and IRI-Plas models over African equatorial and low latitude region They found that the diurnal and seasonal structures of modeled TEC follow quite well with the observed TEC in all the stations. Tariku [24] carried out analysis on GPS-VTEC variation and compare the results with the latest version (IRI-2012) model and the IRI-NeQuick topside model over equatorial regions of Uganda during a very low and a high solar activity year. There could not be found a study that carries out a comparative study of the GPS-TEC measurements, NeQuick-2 and the IRI-Plas modeled data over low and equatorial latitudes regions with different longitudes.
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