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Gap formation around Ω_e/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory

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Earth and Planetary Physics 2020年第2期4卷 138-150页

作者： konrad sauer Klaus Baumgartel Richard Sydora Max-Planck-Institute for Solar System Research GöttingenGermany(up to 2005 Leibnitz-Institut für Astrophysik(AIP) PotsdamGermany(up to 2008 Institute for Geophysical Research University of AlbertaEdmontonCanada

In this paper we show that two significant phenomena of magnetospheric chorus emission can be explained by the participation of beam-like electron structures,created by Landau-resonant interaction with growing oblique whistler *** first concerns the widely observed spectral gap near half the electron cyclotron frequency Ωe;the second is related to the observation of very obliquely propagating lower-band waves that cannot be directly generated by temperature *** the gap,kinetic dispersion theory reveals that interference of the beam-related cyclotron mode ω~Ωe-kVb with the conventional whistler mode leads to mode splitting and the appearance of a ’forbidden’ area in the ω-k *** the beam velocity appears as an essential *** is directly related to the phase velocity of the most unstable whistler wave mode,which is close to VAe/2 for sufficiently hot electrons(VAe is the electron Alfven velocity).To clarify the second point,we show that Landau-resonant beams with Vb Vb

关键词： important role play Landau-resonant electrons modification of the electron distribution function gap formation at half the electron cyclotron frequency

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Frequency Bands and Gaps of Magnetospheric Chorus Waves Generated by Resonant Beam/Plateau Electrons

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Journal of Modern Physics 2022年第6期13卷 864-891页

作者： konrad sauer Huayue Chen Eduard Dubinin Quanming Lu CAS Key Laboratory of Geoscience Environment School of Earth and Space Sciences University of Science and Technology of China Hefei China CAS Center of Excellence in Comparative Planetology Hefei China Max-Plnack Institute for Solar System Research G&ouml ttingen Germany

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 analysing the modified dispersion characteristics these changes are discussed. Supported by particle simulations and space observations, it is assumed that in the electron distribution function at the resonance velocity a plateau-like beam is formed. Because of the weakness of the beam, the term “beam/plateau population (b/p)” is used. By solving the kinetic dispersion relation of whistler waves in electron plasmas with 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. Because of the bi-directional excitation of whistler waves by temperature anisotropy, one has to distinguish between up- and downstream populations and accordingly between two b/p modes. The interaction of the beam-shifted cyclotron mode ω= Ωe + k⋅Vb (V bVb 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

关键词： Radiation Belts Waves Whistlers Chorus

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