Newly-observed features of radiation belt particle variations during the 25th solar cycle based on 6 years’ CSES data

Earth’s radiation belt is filled with high-energy electrons and protons, the particle fluxes distributions and dynamic variations are significantly modulated by solar activities. Based on high-precision China Seismo-Electromagnetic Satellite (CSES) satellite data from 2019 to 2024, a statistical analysis of radiation belt electrons and protons is conducted to investigate their long-term responses to space weather events and solar cycle variations. Firstly, During the solar minimum, high-energy electrons in the outer radiation belt exhibit a pronounced ~27-day recurrence, which is strongly correlated with recurrent solar wind speed enhancements. Secondly, Proton fluxes in the inner radiation belt exhibit an inverse correlation with solar activity, primarily due to enhanced atmospheric neutral density and increased Coulomb collisions during solar maximum. Thirdly, the observed day-night asymmetry in proton fluxes is attributed to the interaction between proton gyromotion and the upper atmosphere molecule collision in low-Earth orbit, as well as the satellite’s orbital and instrument viewing geometry. Additionally, a distinct and persistent double-peaked structure is reported in the low-energy (2-10 MeV) protons of the inner belt, which differs from traditional radiation belt models, but is consistent with the National Oceanic and Atmospheric Administration (NOAA-19) satellite observations. This structure may be related to the weakened magnetic field on the southeastern side of the South Atlantic Anomaly (SAA). These results provide new insights for understanding of the dynamic variations and structural complexity of radiation belt particles associated with space weather activities.