Excitation of Dayside Chorus by Energetic Electrons Originating from the Plasmasheet

Abstract:

Previous studies suggest that dayside chorus at relatively higher L shells can be generated at high magnetic latitudes within the minimum magnetic field region, but the generation mechanism for dayside chorus at lower-shells still remains an open question. Here, we report two events on dayside chorus and energetic electrons during storm periods: 06-07 March 2016 and 20-21 January 2016. The Van Allen probes observed the dayside chorus intensification at region of L = 3.0-6.3, MLT = 5.6-13.5, with a lower frequency band 0.1-0.5 f_ce and a peak spectral density ~10^-4 nT²/Hz. Meanwhile, (~1-100 keV) electrons displayed enhancements in fluxes and anisotropy when they were injected from the plasmasheet and drift from midnight through dawn toward the noon sector. Using a kappa distribution to model the observed electron data, we calculate the growth rate of field-aligned propagating dayside chorus, which shows that the upper cutoff and peak wave frequencies display a similar pattern to the observations with a peak local growth rate ω_i /Ω_ce above 1.55 ×10^-3. The current results tend to imply that the observed lower-shell dayside chorus waves can be excited by the anisotropic electrons originating from the plasmasheet in the course of drift from nightside to dayside sector.