Direct Observations of Energetic Electron Scattering and Precipitation Due To Whistler‐Mode Waves in the Dayside High‐Density Regions

Abstract

The flux of energetic electrons in the Earth's magnetosphere changes dynamically. Electron fluxes in the Earth's magnetosphere are subject to various source and loss processes (McIlwain, 1966(McIlwain, , 1996. Energetic electrons of the inner magnetosphere are distributed in two distinct zones separated by a radially confined region of depleted flux referred to as the slot (Van Allen, 1959;Van Allen & Frank, 1959). Under geomagnetically active conditions, the slot region is filled by enhanced source processes, while during subsequent quiet conditions, the injected energetic electrons are decayed due to radial diffusion and precipitation into the Earth's atmosphere (Baker et al., 1998(Baker et al., , 2004. Numerous studies have unveiled that wave-particle interactions play an important role in the loss of energetic electrons and the formation of the radiation belt structure. The quasi-linear theory predicts that energetic electrons are scattered into the loss cone by plasma waves (Kennel, 1969;Kennel & Petschek, 1966) and precipitate into the atmosphere (Abel & Thorne, 1998;Millan & Thorne, 2007;Summers et al., 2007). The quasi-linear theory describes particle transport in kinetic energy and pitch angle space, under the assumption of stochastic dynamics and a uniform background magnetic field. The ratio of the electron gyrofrequency to the electron plasma frequency as a function of the background electron density and magnetic field intensity is important to control the wave growth and propagation, the wave-particle-resonance conditions, and the resonant diffusion curves of electrons in the velocity space. For more detailed information, please refer to previous studies (e.g., Kennel, 1969;Summers et al., 1998;Storey, 1953). Previous observations have shown that in the plasma trough, where the electron density is low, whistler-mode chorus waves (