Coupled Thermosphere–Ionosphere–Plasmasphere Disturbances During the April 2023 Geomagnetic Storm: A Ground‐Based Multiparametric Study Across the American and European Sectors

Abstract

The April 2023 geomagnetic storm significantly impacted the thermosphere‐ionosphere system, particularly over South America and midlatitude regions. This study analyzes ground‐based geomagnetic and ionospheric data, alongside Swarm satellite measurements, to investigate the physical mechanisms driven by intense solar wind energy input. Magnetic field analysis, with ring current contributions removed, identified two equatorial electrojet enhancements and counter electrojet events during 23, 24 April. On 23 April, an enhanced eastward equatorial electric field, reflected by an intensified equatorial electrojet, drove a poleward shift of the Equatorial Ionization Anomaly crest, increasing electron density over Tucumán. Conversely, a daytime counter electrojet on 24 April caused electron density depletion over Cachoeira Paulista. At midlatitudes, the THERION method was applied to retrieve thermospheric parameters, including neutrals' composition (O, O ₂ , N ₂ ), exospheric temperature, and vertical plasma drift. Results indicate that the observed electron density depletion was primarily driven by a reduction in atomic oxygen and increased molecular nitrogen, with neutral density rises at 300 km dominated by (N ₂ ) enhancement. Spatial variations across Europe and North America highlight the role of equatorward winds in transporting disturbed neutral composition. These dynamic processes pushed the midlatitude ionospheric trough toward unusually low latitudes, indicating a rapid shrinkage of the plasmasphere, and a severely depleted zone was formed in its wake, reducing the efficiency of ionosphere‐to‐plasmasphere refilling during the recovery phase. These findings provide a multiinstrument characterization of F2‐layer storm responses within the coupled thermosphere‐ionosphere‐plasmasphere system.