A Tutorial Review of Cyclotron Resonance Interactions Between Magnetospheric Energetic Electrons and Electromagnetic Waves (Whistlers, Hiss, Chorus and VLF Transmitter Signals) Causing Electron Precipitation and Perturbations to the Upper Atmosphere

The concept of cyclotron resonance near the equatorial plane of the Earth’s magnetosphere between whistlers and energetic electrons originated in the 1960s. Since then, the subject has advanced substantially, with experimental, theoretical and computer modelling studies. A chronological review is undertaken not only of the basic physics of gyro resonance but also of very-low-frequency (VLF) radio observations made on the ground and measurements made by various rocket and satellite instruments of the fluxes of precipitating energetic electrons and whistler-mode waves. Lightning-induced electron precipitation (LEP) contributes appreciably to the dynamics (i.e., the acceleration, transport and loss) of trapped Van Allen radiation belt electrons. However, plasmaspheric hiss (at L < 4.5, for quiet to moderate activity conditions) and chorus (generally at L > 4.5, beyond or outside the plasmasphere and often associated with auroral phenomena) are believed to be more important overall than LEP in causing the precipitation of energetic electrons from the magnetosphere at L > 3.8. The gyro resonant interaction between the VLF radio transmitter signals near the equatorial plane and energetic electrons also contributes appreciably to their loss. With LEP being the major cause, each plays a role in the formation of the slot in the radiation belts at L ~ 2.5. The mechanisms whereby precipitating energetic electrons perturb the physics and chemistry of the mesosphere and D-region ionosphere are also briefly reviewed.