Seasonal Variations in Equatorial Ionospheric Response to Geomagnetic Storms Using GNSS ROTI Observations

This study investigates the equatorial ionospheric response to geomagnetic storms using the rate of change of total electron content (TEC) index (ROTI) derived from Global Navigation Satellite Systems (GNSS) data as a measure of ionospheric irregularities. TEC data were collected from GNSS stations across Nigeria, with days classified as quiet (|Dst| < 30 nT) or disturbed (|Dst| ≥ 50 nT), analyzed separately for daytime and nighttime periods. The response to the geomagnetic storm on February 19, 2014, was examined, along with three sudden storm commencements (SSCs) on February 15, 20, and 23, and a high-speed solar wind event on February 19. Findings indicate that geomagnetic storms did not inhibit irregularities but partially suppressed them during the storm’s initial and recovery phases, with irregularities peaking during the main phase. Higher ROTI values were recorded during the March equinox compared to the September equinox, under both quiet and disturbed conditions. Irregularities were generally suppressed on disturbed days during the September equinox but were more prevalent during the March equinox. The December solstice exhibited an overall inhibition of irregularities, contrasting with equinox patterns. Morning ROTI values remained below 0.35 TECU/min, while daytime values ranged from 0.35 to 0.8 TECU/min, indicating moderate irregularities. This study provides insights crucial for improving GNSS reliability in equatorial regions. Continuous monitoring, expanded GNSS networks, and predictive models are recommended to mitigate storm-induced disruptions to communication and navigation systems.