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Frequency bands and gaps of magnetospheric chorus waves generated by resonant beam/plateau electrons
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  • Konrad Sauer,
  • Huayue Chen,
  • Eduard Dubinin,
  • Quanming Lu
Konrad Sauer
up to 2005: MPI for Solar System Research

Corresponding Author:sauer.ka@gmail.com

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Huayue Chen
CAS Key Laboratory of Geoscience Environment, School of Earth and Space Sciences, University of Science and Technology of China,
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Eduard Dubinin
Max-Planck-Institute for Solar System Research
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Quanming Lu
University of Science & Technology of China
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In this paper, the modifications of the whistler dispersion characteristics are investigated which arise if resonant electrons are taken into account. The following chain of processes is emphasized: Generation of whistler waves propagating at different angles to the magnetic field and their nonlinear interaction with resonant electrons result in the appearance of modulated electron beams in the background plasma. As a result, the dispersion characteristics of waves in this new plasma might be significantly changed. By solving the kinetic dispersion relation of whistler waves in electron plasmas with so-called beam/plateau (b/p) populations, the associated modifications of the whistler dispersion characteristics are presented in diagrams showing, in particular, the frequency versus propagation angle dependence of the excited waves. It is important to point out the two functions of the b/p populations. The interaction of the beam-shifted cyclotron mode ω = Ωe + k·Vb (Vb<0, Vb is the b/p velocity, Ωe: electron cyclotron frequency)) with the whistler mode leads to enhanced damping at the ω-k point where they intersect. This is the origin of the frequency gap at half the electron cyclotron frequency (ω~Ωe/2) for quasi-parallel waves which are driven by temperature anisotropy. Furthermore, it is shown that the upstream b/p electrons alone (in the absence of temperature anisotropy) can excite (very) oblique whistler waves near the resonance cone. The governing instability results from the interaction of the beam/plateau mode ω=k·Vb (Vb>0) with the whistler mode. Relations to recent and former space observations are discussed.