Near‐equatorial pitch angle diffusion of energetic electrons by oblique whistler waves

Abstract

The pitch angle scattering of trapped, energetic electrons by obliquely propagating whistler waves in the equatorial regions of the plasmasphere is investigated. Storm‐injected electrons moving along field lines near the equator interact with electromagnetic waves whose frequencies are Doppler‐shifted to some harmonic of the cyclotron frequency. The wave normals are distributed almost parallel to the geomagnetic field. Waves grow from the combined contributions of a large reservoir of energetic electrons that are driven into the loss cone by the highest‐harmonic interactions permitted to them. Relativistic, quasi‐linear theory is applied to obtain self‐consistent equations describing the temporal evolution of waves and particles over time scales which are longer than the particle bounce time and group time delay of the waves. The equilibrium solutions and their stability are studied, considering the reflection of the waves by the ionosphere and the coupling of multiple harmonic resonances. The contributions of nonlocal wave sources are also included in the theory. Numerical computations based on our theoretical analysis for regions inside the plasmasphere (L ≤ 2) and near the plasmapause (L ∼ 4.5) and for the first three harmonic resonances are presented.