Superposed epoch analysis of GPS ionospheric TEC and scintillations over low latitude Indian region during multiple geomagnetic storm events

Low-latitude ionospheric irregularities during geomagnetic storms are a significant concern for global navigation satellite systems (GNSS) because they degrade positional accuracy and integrity of the Positioning, Navigation, and Timing (PNT) services. GNSS is an effective ionospheric remote-sensing tool to measure the ionospheric total electron content and ionospheric amplitude and phase scintillations by ground-based GNSS receivers by receiving GNSS satellite signals. Amplitude Scintillation Index S4 was obtained in real-time from twenty-six dual-frequency global positioning system (GPS) receivers specialized in ionospheric scintillation and total electron content (TEC) monitors (GISTMs) receivers (GPS stations) deployed as part of the GPS-aided geo-augmented navigation (GAGAN) over the Indian region. 30 geomagnetic storm events of strong, moderate and weak intensity are identified with SYM-H geomagnetic parameter during the 2014 and 2016. Superposed epoch analysis of ionospheric VTEC and S4 observations of 30 geomagnetic storm events is investigated. The response of ionospheric TEC and S4 are analyzed during geomagnetic storms' primary, initial, and recovery phases. The 2D SEA ionospheric scintillations results indicate that ionospheric scintillations features are enhanced between +/- 10 h epoch, whereas suppression of the trend is observed between +/- 20 to +/- 40 h epoch. The correlation analysis of SYM-H, AE, and IMF-Bz with VTEC and S4 indicates the influence of storm time response characteristics. This work's outcome would help in understanding comprehensive ionospheric variability during weak, moderate and strong geomagnetic storm events.