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Nonlinear fundamental and harmonic cyclotron resonant scattering of radiation belt ultrarelativistic electrons by oblique monochromatic EMIC waves
Author(s) -
Wang Geng,
Su Zhenpeng,
Zheng Huinan,
Wang Yuming,
Zhang Min,
Wang Shui
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2016ja023451
Subject(s) - physics , electron , cyclotron resonance , cyclotron , scattering , pitch angle , harmonic , atomic physics , computational physics , harmonics , resonance (particle physics) , electron cyclotron resonance , optics , nuclear physics , geophysics , quantum mechanics , voltage
Cyclotron resonant scattering by electromagnetic ion cyclotron (EMIC) waves has been considered to be responsible for the rapid loss of radiation belt high‐energy electrons. For parallel‐propagating EMIC waves, the nonlinear character of cyclotron resonance has been revealed in recent studies. Here we present the first study on the nonlinear fundamental and harmonic cyclotron resonant scattering of radiation belt ultrarelativistic electrons by oblique EMIC waves on the basis of test particle simulations. Higher wave obliquity produces stronger nonlinearity of harmonic resonances but weaker nonlinearity of fundamental resonance. Compared to the quasi‐linear prediction, these nonlinear resonances yield a more rapid loss of electrons over a wider pitch angle range. In the quasi‐linear regime, the ultrarelativistic electrons are lost in the equatorial pitch angle range α eq <75°, nearly independent of wave normal angle ψ . In contrast, the upper pitch angle cutoff of nonlinear losses tends to increase with the wave normal angle increasing, which is about α eq =82° at ψ = 0° and α eq >87.5° at ψ = 20° and 40°. At the resonant pitch angles α eq <75°, the difference between quasi‐linear and nonlinear loss timescales tends to decrease with the wave normal angle increasing. At ψ = 0° and 20°, the nonlinear electron loss timescale is 10% shorter than the quasi‐linear prediction; at ψ = 40°, the difference in loss timescales is reduced to <5%.