Transient distortions of the South Atlantic Anomaly radiation environments driven by electric fields

Energetic electrons in Earth's inner radiation belt pose significant hazards to spacecraft systems, with the strongest radiation in low-Earth orbit (LEO) mostly confined to the South Atlantic Anomaly (SAA) region. Once considered stable, the inner belt is now understood to exhibit significant variability. Using data from the low-Earth-orbit Macau Science Satellite-1 mission, we report transient distortions of the SAA radiation environments, observationally characterized by enhanced fluxes of energetic electrons outside the traditional SAA radiation region, appearing either attached to or detached from its boundary. We show that these distortions can be explained by large-scale electric-field perturbations that adiabatically alter the electron mirror heights, which can be further modulated by ultra-low-frequency waves. Test-particle simulations successfully reproduce the observational features and provide crucial constraints on properties of the associated electric fields. These findings reveal a distinct manifestation of inner-belt variability, extending the electron radiation risks beyond the expected boundaries of the SAA radiation environments.