Evaluation of whistler mode chorus amplification during an injection event observed on CRRES

The excitation of nightside whistler mode chorus emissions in the low-density region outside the plasmapause is investigated during an injection of plasma sheet electrons into the inner magnetosphere. CRRES data of the electron phase space density (PSD) over the LEPA energy range between 0.1 keV and 30 keV are used to develop an analytical model for the distribution function of injected low-energy electrons. The path-integrated growth of chorus waves is then evaluated with the HOTRAY code by tracing unducted whistler mode chorus waves in a hot magnetized plasma. The results indicate that newly injected electrons are responsible for the intensification of lower-band whistler mode chorus. However, slightly higher electron anisotropy than that obtained from the 5 min-averaged electron PSD data is required to reproduce the observed wave intensity during an injection event. We suggest that the injected electron anisotropy is reduced due to pitch angle scattering by the enhanced chorus waves within the 5-min interval over which the CRRES data are analyzed.

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