TEC derived from GPS network in India and comparison with the IRI

Total electron content (TEC) measured simultaneously using Global Positioning System (GPS) satellites at 18 locations in North-South and East-West directions across the Indian subcontinent during 2003–2004 was used to study the diurnal, seasonal, and annual TEC variations. The TEC exhibits features like the equatorial noon time bite-out, annual and semiannual variations, the equatorial ionization anomaly, and day-to-day variability. Daytime variability is less at and near the equator than at the crest of the anomaly, whereas nighttime variability is high compared to the daytime variability in all seasons and at all latitudes. The time of occurrence of the diurnal maximum in TEC also varies with season. Measured TEC were compared with those predicted by the International Reference Ionosphere (IRI). It was observed that while IRI TEC is greater than those measured at about all local times, the TEC predicted by the IRI with a set of regional foF2 coefficients are closer to the measured values.