Low-Latitude Ionospheric Disturbances and EIA Expansion During Consecutive Geomagnetic Storms in November 2025 Using BDS-GEO Satellites over the Eastern Hemisphere

This study investigates the low-latitude ionospheric response over the Eastern Hemisphere during two successive geomagnetic storms on 12–13 November 2025. BDS-GEO observations from 20 GNSS stations, CODE GIM data, Swarm satellite observations, and simulations from the TIEGCM and HWM14 models were integrated to investigate regional ionospheric disturbances, single-station responses, and Equatorial Ionization Anomaly (EIA) evolution. During the first storm, with SYM-H reaching −254 nT, EIA intensification and poleward expansion beyond ±20° magnetic latitude were observed, with VTEC approaching 100 TECU at stations over Australia and rTEC exceeding 80% over Australia and the adjacent Pacific Ocean. Swarm observations showed TEC decreases within the EIA crest region and TEC increases in the surrounding areas. In contrast, the second storm, with SYM-H reaching −154 nT, produced disturbances with lower amplitudes, mainly characterized by localized positive TEC anomalies near the magnetic equator within 100°E–180°E, together with negative TEC anomalies in the surrounding low-latitude regions. The first storm was associated with southward IMF Bz reaching −54 nT and electrodynamic uplift related to PPEF, which contributed to the superfountain effect, whereas the second storm was influenced by residual disturbed neutral winds, reduced O/N2 ratios at low latitudes, and the preconditioned ionospheric state inherited from the first storm. These results demonstrate that successive geomagnetic storms can produce different ionospheric responses in terms of intensity, spatial morphology, and driving mechanisms, highlighting the event dependence and regional variability of low-latitude ionospheric storm responses. BDS-GEO observations offer distinct advantages for monitoring localized ionospheric disturbances over the Eastern Hemisphere.