Latitude-Dependent Ionospheric Dynamics During the Moderate Geomagnetic Storm of 21–22 March 2026 over the Indian Longitude Sector

This study examines the highly variable and latitude-dependent ionospheric response to the moderate geomagnetic storm that occurred on 21–22 March 2026 over the Indian longitudinal sector using combined observations of Global Navigation Satellite System (GNSS) derived Total Electron Content (TEC) and Swarm electron density profiles. During the main phase on 21 March, pronounced positive ionospheric storm effects were observed at mid-latitudes, with Vertical TEC (VTEC) enhancements reaching up to 35 TECU, while notable negative storm effects occurred near the Equatorial Ionization Anomaly (EIA) crest region. These simultaneous observations from mid-latitude and EIA regions are attributed to the combined effects of Prompt Penetration Electric Fields (PPEFs) and the possible presence of storm-induced equatorward neutral winds. The low-latitude region exhibited moderate daytime ionospheric variations throughout the storm period, despite the presence of PPEFs. Interestingly, electron density profiles from Swarm-A and Swarm-C satellites showed a reduction around the EIA region, along with elevated electron densities near the magnetic equator during the evening period of the storm main phase. On 22 March, the storm-time ionospheric response transitioned into a more complex mixed pattern, with recovery to near-quiet levels at most stations. Moderate VTEC enhancements in the EIA region and distinct mid-latitude electron density increases are likely attributed to the thermospheric composition changes characterized by an increased O/N2 ratio. These findings highlight the synergistic roles of electrodynamic forcing, neutral wind circulation, and altered thermospheric composition in modulating storm-time ionospheric behavior. This study provides valuable insights into complex plasma dynamics at low- and mid-latitudes, with important implications for GNSS-based navigation and communication systems during geomagnetic disturbances.