Generation of Lower L Shell Dayside Chorus by Energetic Electrons From the Plasma Sheet

摘要

abstract_textpCurrently, the generation mechanism for the lower L shell dayside chorus has still remained an open question. Here we report two storm events: 6-7 March 2016 and 20-21 January 2016, when Van Allen Probes observed enhanced dayside chorus with lower and higher wave normal angles (the angles between the wave vector and the geomagnetic field) in the region of L = 3.5-6.3 and MLT = 5.6-13.5. Hot and energetic (similar to 1-100keV) electrons displayed enhancements in fluxes and anisotropy when they were injected from the plasma sheet and drifted from midnight through dawn toward the dayside. Calculations of chorus local growth rates under different waves normal angles show that the upper cutoff and peak wave frequencies display similar patterns to the observations. Chorus growth rates maximize for the parallel propagation and drop with increasing wave normal angles. The current results confirm that the observed lower L shell dayside chorus can be excited by anisotropic electrons originating from the plasma sheet in drifting from the nightside to the dayside./p/abstract_text