Abstract
We identified 28 discrete electron events (DEEs) with enhanced fluxes at ∼50–200 keV in the high-altitude cusp/polar cap/lobe, using the electron measurements by the BeiDa Image Electron Spectrometer (BD-IES) instrument onboard an inclined (55°) geosynchronous orbit (IGSO) satellite from October 2015 to January 2016. We find that among the 28 DEEs, 22 occur in the nightside and mostly in the northern cusp/polar cap/lobe, while 6 occur in the dayside and all in the southern cusp; 24 events correspond to an average interplanetary magnetic field (IMF) component B z>0, 3 correspond to an average IMF B z<0, and 1 has no OMNI IMF data. In these DEEs, the observed average omnidirectional electron differential flux generally fits well to a power-law spectrum, J∼E −γ, with the spectral index γ ranging from 2.6 to 4.6, while the average electron flux varies over three orders of magnitude from event to event. The spectral index of these cusp DEEs are (strongly) larger than the spectral index of solar wind superhalo electrons (radiation belt electrons) observed by the WIND 3D Plasma & Energetic Particle instrument (the BD-IES). At ∼110 keV, the electron flux of DEEs in the cusp/polar cap/lobe shows a weak positive correlation with the solar wind superhalo electron flux but no obvious correlation with the radiation belt electron flux. These results suggest that these DEEs probably originate from transient processes acting on the solar wind superhalo electrons, e.g., the mid/high-latitude reconnection.
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Wang, L., Zong, Q., Shi, Q. et al. Discrete energetic (∼50–200 keV) electron events in the high-altitude cusp/polar cap/lobe. Sci. China Technol. Sci. 60, 1935–1940 (2017). https://doi.org/10.1007/s11431-017-9119-x
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DOI: https://doi.org/10.1007/s11431-017-9119-x