Responses of geostationary orbit energetic electron fluxes to chorus waves under different geomagnetic conditions

Abstract

We investigate the flux evolution of geostationary orbit energetic electrons during a strong storm on 24 August 2005 (event A, the storm index Dst -50 nT, average AE=320 nT). Data collected by LANL and GOES-12 satellites show that energetic electron fluxes increase by a factor of 10 during the recovery phase compared to the prestorm level for both events A and B. As the substorm continued, the Cluster C4 satellite observed strong whistler-mode chorus waves (with spectral density approaching 10−5 nT2/Hz). The wave amplitude correlates with the substorm AE index, but is less correlated with the storm Dst index. Using a Gaussian distribution fitting method, we solve the Fokker-Planck diffusion equation governing the wave-particle interaction. Numerical results demonstrate that chorus waves efficiently accelerate ∼1 MeV energetic electrons, particularly at high pitch angles. The calculated acceleration time scale and amplitude are comparable to observations. Our results provide new observational support for chorus-driven acceleration of radiation belt energetic electrons.