Observed (GPS) and modeled (IRI and TIE-GCM) TEC trends over southern low latitude during solar cycle-24

Abstract

The Total Electron Content (TEC) derived from the Global Positioning System (GPS) measurements during the solar cycle-24 at COCO Island (12.20⁰ S, 96.80⁰ E) are compared with those of International Reference Ionosphere-2016 (IRI-2016) model and Thermosphere Ionosphere Electrodynamics General CirculationModel (TIE-GCM). TEC data derived from the above two models follow the nature of observed variations with considerable divergences in amplitudes. The precision of model TEC in reference to GPS TEC is discussed using a correlation coefficient, mean difference, root mean square error, and relative deviation module mean techniques. The randomness of predictions is found to be biased by the solar cycle, season, and local time. The simulated values showed better accuracy during the low solar activity and night hours. This study is an extension of Rao et al. (2019b), in which we reported similar study of TEC variability at the northern low latitude station. First of all, it is observed from two studies that the magnitude of TEC is greater at the southern low latitude than at the northern low latitude. Also the correlation between GPS TEC/ IRI TEC and F10.7 flux is determined to be greater at northern low latitude station compared to southern low latitude station. However, TIE-GCM TEC values are found to be slightly more correlated with F10.7 flux at southern low latitude station compared to northern low latitude station. With regard to seasonal variation, semiannual oscillations in TEC are found to be coherent on both sides of the equator. However, the winter anomaly is not observed or predicted by models at the southern low latitude whereas it is observed to be a solar flux-dependent feature at the northern low latitude. The IRI model closely follows seasonal trends of TEC whereas TIE-GCM over-predicted TEC during solstices at the northern low latitudes. Models TEC deviations are found to be lesser at the southern low latitude compared to northern low latitude.