Distribution of energetic electrons in the near earth space: New observations from the BeiDa Imaging Electron Spectrometer and the Van Allen Probes

Abstract

We study the distribution of magnetospheric electrons using data from the BeiDa Imaging Electron Spectrometer (BD-IES) onboard a Chinese navigation spacecraft and the Magnetic Electron Ion Spectrometer (MagEIS) onboard the Van Allen Probes (VAP). While the MagEIS instrument monitors electron flux in the inner magnetosphere (L∗<6), the BD-IES instrument extends the range of measurement beyond the geosynchronous distance (6<L∗<9). Utilizing one year of the multi-spacecraft data, the distribution of electron phase space density (PSD) of wide spatial and energy coverage is statistically derived for the first time. Evident peaks are identified in the radial PSD profiles of energetic electrons (μ>50MeV/G) at L∗~5.5, with the inner and outer sides of the PSD peaks unambiguously observed by MagEIS and BD-IES respectively. These peaked distributions confirm that local acceleration plays an important role in the electron dynamics. Besides, the electron spectra in the vicinity of the PSD peak are harder, with spectral indexes of ~−2.5. The spectral index drops to ~−4 inside L∗~3. This softer spectrum indicates less acceleration and/or more loss in the most inner part of the magnetosphere. The new observational results from the BD-IES, incorporated with VAP data, provide us with a more comprehensive view of the energetic electrons in the near Earth space.