Effects of the May 2024 Solar Storm on the Earth's Radiation Belts Observed by CALET on the International Space Station

Abstract In May 2024, extraordinary solar activity triggered a powerful solar storm, impacting Earth and producing the extreme geomagnetic storm of 10‐11 May, the most intense since 2003. This had significant effects on the magnetosphere, leading to the creation of a new long‐lasting component of relativistic electrons and to flux changes in the South‐Atlantic Anomaly. Here we present radiation‐belt observations made by the Calorimetric Electron Telescope (CALET) on the International Space Station. Specifically, we took advantage of the count rates from three layers of the CALET charge detector and imaging calorimeter. We show that the new electron storage ring extended to energies in the multi‐MeV range and down to McIlwain's L = 2.2, well below the nominal slot‐region barrier of L = 2.8, and persisted for several months, depending on energy. The evolution of the new radiation‐belt configuration over time was characterized by estimating the decay rates as a function of energy and L .