Outer radiation belt sub-relativistic electron flux dynamics during the magnetic storm in May 2024

One of the most intense geomagnetic storms in recent history occurred on 10–11 May 2024. With a peak negative Sym-H excursion below − 500 nT (Dst = − 412 nT), this event was the second largest geomagnetic storm recorded in the space era. In this study, we analyze the dynamics of sub-relativistic electron fluxes before, during, and after this event using data from the Avion CubeSat, which is part of the Moscow State University multi-satellite constellation “Sozvezdie–270”. The Avion 6U CubeSat deployed the DeCoR instrument, comprising three scintillation spectrometers optimized for measurements of sub-relativistic and relativistic electrons in the energy range from 40 keV to 2 MeV. During the storm, Avion observed a strong enhancement of sub-relativistic electron fluxes, which we interpret as evidence for the formation of a new radiation belt. We found that the maximum intensity of sub-relativistic electrons occurred at L ~ 2.5–3, in agreement with the Tverskaya statistical relation, which describes the dependence of the position of post-storm outer radiation belt maximum on the minimum Dst value reached during the storm. We also observed that, during the storm, the boundaries of the sub-relativistic electron enhancements extended into the region ( L < 2). Because the experiment primarily recorded isotropic fluxes, we cannot completely exclude the possibility that the observed variations were associated with precipitation of particles entering the drift loss cone. Nevertheless, the obtained results complement existing studies of this superstorm and provide valuable experimental evidence for developing models of physical processes occurring during magnetic storms.