Non-Adiabatic Acceleration of Injected Electrons in the Inner Magnetosphere: Joint Observations by the Van Allen Probe and the BeiDa Imaging Electron Spectrometer

We present joint observations of a substorm injection event on 5 February 2016. The enhancements of energetic electron (similar to 30 to similar to 300 keV) fluxes, the drift echoes of the injected electrons, and the quasi-monochromatic ultralow frequency oscillations embedded in the flux variations were simultaneously observed by the BeiDa Imaging Electron Spectrometer and the Van Allen Probe B. These vivid features of substorm injection were concretely captured by multiple spacecraft within the geosynchronous distance for the first time. The radial separation of the spacecraft (similar to 0.3 R-E) allowed for a quantitative comparison of the electron flux and phase space density (PSD) across different drift shells. It is found that a more intense increase of equatorial PSD occurred at the lower L-shell (L* similar to 5.5), which indicated a non-adiabatic acceleration of the injected electrons in the inner magnetosphere.