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|Title:||Interactions between whistler-mode signals and magnetospheric energetic electrons: An overview of some experimental observations and theoretical interpretations|
|Authors:||Rycroft, Michael J|
|Keywords:||Backward wave oscillator;ELF/VLF chorus;Cluster mission;DEMETER microsatellite;Electron precipitation;Equatorial gyroresonance;High frequency Active Auroral Research Program (HAARP);Man-made whistler mode waves;Natural whistlers;Nonlinear plasma physics phenomena;Pitch angle diffusion;Siple (Antarctica);Triggered VLF emissions;Van Allen radiation belt electrons|
|Abstract:||The last forty years have seen remarkable developments in our understanding of the Doppler-shifted cyclotron resonance interactions between ducted whistler-mode radio signals travelling in one direction along a dipolar geomagnetic flux tube (1.5 < L < ~ 6) and Van Allen radiation belt electrons travelling in the other. These signals range from natural whistlers generated by lightning discharges and sweeping in frequency to (apparently) spontaneously generated hiss and chorus, and to single frequency signals from ground-based VLF radio transmitters. In these interactions, whistler-mode waves of audio frequency are amplified and the electrons’ pitch angles are reduced, some being pushed into the loss cone to perturb the lower ionosphere at the foot of the flux tube where the interaction has taken place. The plasma instability is established at or close to the equatorial plane of the magnetosphere. With feedback mechanisms, cyclotron maser action, therefore, takes place. In many cases, this action produces signals of rising frequency (and occasionally of falling frequency). Observations have been made of aspects of these interactions on rockets and on Earth-orbiting satellites, complemented by radio observations made on the ground. Such observations are reviewed for naturally occurring whistlers, chorus and man-made signals, e.g. from the Siple transmitter in Antarctica and the NWC transmitter in Australia. Self-consistent nonlinear theoretical analyses of these interactions, involving broad electron distribution functions, have been undertaken and numerical simulations performed. An overview of these recent developments is also provided.|
|ISSN:||0975-105X (Online); 0367-8393 (Print)|
|Appears in Collections:||IJRSP Vol.40(5) [October 2011]|
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