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Variability of Ionospheric Total Electron Content at Low-latitude Station During Twin Solar Maxima and Solar Minima of The 24th Solar Cycle and its Comparison With Different Versions of IRI Models

In this study, we compared the modelled total electron content (TEC), i.e. ionospheric TEC derived from the latest International Reference Ionosphere (IRI) versions (viz. IRI-2007, IRI-2012 and IRI-2016) with TEC derived by the International GNSS Service (IGS) receivers at a low-latitude station, namely Pathum Wan, Thailand (code-CUSV; lat. 13.74°N, long. 100.54°E) during the twin solar maxima 2012 and 2014, and the solar minima 2017 of the 24th solar cycle. We observed that the modelled TEC results were slightly underestimated than those derived by global positioning system (GPS), during the maxima and minima periods. It was also observed that the modelled TEC and GPS TEC followed a similar sinusoidal pattern with crests in the equinox months and troughs in the solstice months. We calculated standard deviation of the modelled TEC from the corresponding GPS TEC during the period. The study shows that the IRI model is more suitable when applied during solar minima period. We also carried out correlation study between modelled TEC and GPS TEC, and obtained a moderate degree of positive correlation. Thus we can conclude that IRI2007 is the most suitable version for the twin solar maxima and the minima periods. Also IRI-2016 is the most suitable model for TEC estimation during geomagnetic storms.