Global Thermosphere–Ionosphere Coupling During the May 2024 Geomagnetic Superstorm: Insights from GIM Observations, SAMI3, and GITM

The geomagnetic superstorm of 10–14 May 2024, the most intense event of Solar Cycle 25 (Dst = −412 nT, Kp = 9), produced severe disturbances throughout the coupled thermosphere–ionosphere system, providing an exceptional opportunity to investigate storm-time plasma dynamics using first-principles numerical models. In this study, the global ionospheric response is investigated using Global Ionosphere Map (GIM) Total Electron Content (TEC) observations together with simulations from the Sami3 is Also a Model of the Ionosphere (SAMI3) and the Global Ionosphere–Thermosphere Model (GITM). The temporal and spatial evolution of TEC, electron density, neutral composition (O/N₂), and thermospheric circulation are analysed throughout the storm. GIM observations reveal rapid development of a global negative ionospheric storm following the storm commencement, with electron density depletion expanding from high to middle latitudes across the Northern Hemisphere, while simultaneous positive TEC disturbances developed over extensive regions of the Southern Hemisphere, producing a pronounced interhemispheric asymmetry. The simulations successfully reproduce the large-scale evolution of TEC, including suppression of the northern Equatorial Ionization Anomaly, redistribution of low-latitude plasma, and subsequent recovery during 13–14 May. GITM simulations further demonstrate significant storm-induced changes in thermospheric composition and enhanced meridional neutral winds that coincide with the observed redistribution of ionospheric plasma. Comparison between observations and model simulations indicates that large-scale thermosphere–ionosphere coupling explains the dominant morphology of the global ionospheric response, whereas regional differences suggest additional influences from prompt penetration electric fields and disturbance dynamo processes. The combined GIM–SAMI3–GITM analysis provides an independent assessment of first-principles modeling during an extreme geomagnetic storm and demonstrates the importance of simultaneously considering neutral atmospheric dynamics and ionospheric plasma processes for improving physics-based space weather prediction.