Assimilation of Ground and Satellite Magnetic Observations Unravels the Ionospheric, Magnetospheric, and Induced Fields During the May and October 2024 Geomagnetic Storms

Abstract The geomagnetic storms of May and October 2024 were the strongest storms of solar cycle 25, with the index as low as −412 nT and auroras down to low latitudes. To investigate these extreme events, we developed a global magnetic field model of magnetospheric, ionospheric, and Earth‐induced contributions obtained by assimilating magnetic observations. To leverage both ground observatory and multi‐satellite magnetic data from the Swarm , CryoSat‐2, GRACE‐FO, and MSS‐1 satellites, we used a new modeling approach to separate the magnetospheric and ionospheric sources, and to model both external and the Earth‐induced fields with a 1‐hr time resolution. The high spatio‐temporal resolution of the model enables investigating the coupling between the mid‐latitude ionospheric and magnetospheric field sources during all phases of the geomagnetic storms. The model reveals the total magnetic field disturbance at satellite and ground altitudes, providing critical input for space weather and a more accurate representation of the geomagnetic field.