Rapid Transport of Energetic Electrons to Low L $L$ -Shells: The Key Role of Electric Fields

The dynamics of the outer radiation belt are traditionally associated with wave-particle resonant interactions, which provide local electron acceleration and losses through very low-frequency waves, and electron radial transport by ultra-low frequency waves. However, these processes cannot explain observations of rapid radial transport of energetic electrons (on a time-scale of a couple of hours), deep into the inner magnetosphere (down to $L\sim 2$, mapping to $\sim 45°$ magnetic latitude in the ionosphere). This transport is likely associated with strong convection electric fields forming around the plasmapause. To investigate these rapid, low-latitude electron transport, we combine low-altitude observations of energetic electron fluxes by the ELFIN CubeSats and DMSP satellites, SuperDARN measurements of ionospheric plasma flows (electric fields), and equatorial measurements of energetic electrons and electric fields by THEMIS. Our findings demonstrate that the rapid filling of the slot region by keV electrons is directly associated with electric field penetration to low latitudes (down to $40-50°$). The proposed electron transport scenario, the direct penetration of energetic electrons by strong, localized electric fields, underscores the importance of ionosphere-magnetosphere coupling in radiation belt dynamics.