Abstract This study analyses the long and short-term variations of ionospheric Total Electron Content (TEC) over Sri Lanka using the routinely published Global Ionospheric Maps (GIMs) from International GNSS Service (IGS) during 2018–2023 that encompasses the transition period from the late declining phase of solar cycle 24 to the early ascending phase of solar cycle 25. The geographic location of Sri Lanka lies in the equatorial region across the Indian longitude sector, influenced by the equatorial ionospheric processes such as Fountain effects, Equatorial Ionization Anomaly (EIA) and Pre-Reversal Enhancement (PRE), etc., underlining it as a strategic location for understanding the critical effects of equatorial electrodynamics and space weather on trans-ionospheric radio signals. We validated GIM TEC with ground-based GPS-TEC at three distinct latitudinal locations in Sri Lanka from October 2017 to September 2018 that exhibited a strong positive correlation ( R ∼0.7) and consistent agreement in diurnal, seasonal, and latitudinal TEC variations. The findings from this study reaffirm the applicability of GIM in the Sri Lankan region, based on which the long-term investigation of GIM TEC variations is conducted to understand the diurnal, seasonal, and latitudinal variability, as well as the effects during the geomagnetic storms. These results showed the recurring pattern in diurnal and seasonal TEC variations, with the significant role of fountain effects at the magnetic equator. The maximum TEC values increased from approximately 50 TECU in 2018 to about 140 TECU in 2023, which shows the progressive solar activity influences on the equatorial ionosphere. Additionally, GIM TEC analysis during two distinct geomagnetic storm events over the period shows significant TEC fluctuations, highlighting its capability to monitor storm-time ionospheric disturbances over the region. This work reinforces the knowledge of ionospheric dynamics in the equatorial region over Sri Lanka, which has been sparsely explored in the literature but could add significance to the understanding and modelling of equatorial and low latitude ionosphere in the Indian longitude sector.
Venujan et al. (Tue,) studied this question.