Gap formation around Ωe/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory
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 waves. The first concerns the widely observed spectral gap near half the...
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| Format: | Article |
| Language: | English |
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Science Press
2020-02-01
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| Series: | Earth and Planetary Physics |
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| Online Access: | http://www.eppcgs.org/article/doi/10.26464/epp2020020?pageType=en |
| _version_ | 1811218476916801536 |
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| author | Konrad Sauer Klaus Baumgärtel Richard Sydora |
| author_facet | Konrad Sauer Klaus Baumgärtel Richard Sydora |
| author_sort | Konrad Sauer |
| collection | DOAJ |
| description | 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 waves. The 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 anisotropy. Concerning 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 space. Thereby the beam velocity Vb appears as an essential parameter. It 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 < VAe/2, which arise in cold plasmas from unstable upper-band waves, are able to generate lower-band whistler mode waves at very oblique propagation (θ ≥ 60°). Our studies demonstrate the important role of Landau-resonant electrons in nonlinear whistler wave generation in the magnetosphere. |
| first_indexed | 2024-04-12T07:09:38Z |
| format | Article |
| id | doaj.art-78968fe19e6e45b28891b1b6b94b08a4 |
| institution | Directory Open Access Journal |
| issn | 2096-3955 |
| language | English |
| last_indexed | 2024-04-12T07:09:38Z |
| publishDate | 2020-02-01 |
| publisher | Science Press |
| record_format | Article |
| series | Earth and Planetary Physics |
| spelling | doaj.art-78968fe19e6e45b28891b1b6b94b08a42022-12-22T03:42:40ZengScience PressEarth and Planetary Physics2096-39552020-02-014213815010.26464/epp2020020Sauer-Konrad-02Gap formation around Ωe/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theoryKonrad Sauer0Klaus Baumgärtel1Richard Sydora2Max-Planck-Institute for Solar System Research, Göttingen, Germany (up to 2005)Leibnitz-Institut für Astrophysik (AIP), Potsdam, Germany (up to 2008)Institute for Geophysical Research, University of Alberta, Edmonton, CanadaIn 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 waves. The 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 anisotropy. Concerning 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 space. Thereby the beam velocity Vb appears as an essential parameter. It 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 < VAe/2, which arise in cold plasmas from unstable upper-band waves, are able to generate lower-band whistler mode waves at very oblique propagation (θ ≥ 60°). Our studies demonstrate the important role of Landau-resonant electrons in nonlinear whistler wave generation in the magnetosphere.http://www.eppcgs.org/article/doi/10.26464/epp2020020?pageType=enimportant role play landau-resonant electronsmodification of the electron distribution functiongap formation at half the electron cyclotron frequency |
| spellingShingle | Konrad Sauer Klaus Baumgärtel Richard Sydora Gap formation around Ωe/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory Earth and Planetary Physics important role play landau-resonant electrons modification of the electron distribution function gap formation at half the electron cyclotron frequency |
| title | Gap formation around Ωe/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory |
| title_full | Gap formation around Ωe/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory |
| title_fullStr | Gap formation around Ωe/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory |
| title_full_unstemmed | Gap formation around Ωe/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory |
| title_short | Gap formation around Ωe/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory |
| title_sort | gap formation around ωe 2 and generation of low band whistler waves by landau resonant electrons in the magnetosphere predictions from dispersion theory |
| topic | important role play landau-resonant electrons modification of the electron distribution function gap formation at half the electron cyclotron frequency |
| url | http://www.eppcgs.org/article/doi/10.26464/epp2020020?pageType=en |
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