Solar Energetic Electrons Entering the Earth’s Cusp/Lobe

Abstract

We present a comprehensive study of three solar energetic electron events observed in the Earth’s cusp/lobe regions by the BeiDa Image Electron Spectrometer (BD-IES) on board a BeiDou satellite in an inclined (55°) geosynchronous orbit in 2015 October, 2015 November, and 2016 January, respectively. In all three events at energies above 50 keV, the electron omnidirectional differential fluxes from BD-IES show a strong (∼0.7–0.9) correlation with the simultaneous electron fluxes from the Wind 3DP instrument in the interplanetary medium, but generally with a smaller intensity. Compared to the Wind 3DP spectra of electron flux versus energy, the BD-IES electron spectra also fit well to a power-law function, , but the power-law spectral index appears to be mostly smaller than the 3DP spectral index, for all three events. These measurements provide the first observational evidence that solar/interplanetary energetic electrons can directly and continuously enter the planet’s cusp/lobe regions and get trapped there, probably leading to a contribution to the energetic electrons and/or seed particles for acceleration in the planetary magnetosphere.