Generation of Lower Harmonic Magnetosonic Waves Through Nonlinear Wave‐Wave Interactions
Abstract Although magnetosonic waves in the Earth's magnetosphere have been well understood by the linear theory, low harmonic magnetosonic waves, which often lack of free energy, can be unusually present. By employing a 1‐D particle‐in‐cell simulation model, we have investigated the generation...
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| Format: | Article |
| Language: | English |
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Wiley
2018-08-01
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| Series: | Geophysical Research Letters |
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| Online Access: | https://doi.org/10.1029/2018GL079090 |
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| author | Xinliang Gao Jicheng Sun Quanming Lu Lunjin Chen Shui Wang |
| author_facet | Xinliang Gao Jicheng Sun Quanming Lu Lunjin Chen Shui Wang |
| author_sort | Xinliang Gao |
| collection | DOAJ |
| description | Abstract Although magnetosonic waves in the Earth's magnetosphere have been well understood by the linear theory, low harmonic magnetosonic waves, which often lack of free energy, can be unusually present. By employing a 1‐D particle‐in‐cell simulation model, we have investigated the generation of those unusual lower harmonic magnetosonic waves in a plasma containing a proton ring distribution. In our simulation, the higher harmonic magnetosonic waves (from~9Ωh to ~12Ωh) are firstly excited due to the unstable proton ring, which can be well explained by the linear theory. Several lower harmonic magnetosonic waves (below 5Ωh), which well separates away from the higher harmonics, soon appear in the system. Those lower harmonics, which do not have any positive linear growth rates, can be generated by a nonlinear mechanism. The bicoherence analysis demonstrates that there is a strong phase coupling among the unusual lower harmonic magnetosonic waves and the magnetosonic waves generated due to the proton ring, supporting the idea that the lower harmonic waves could be driven by the wave‐wave couplings of the generated magnetosonic waves. This wave‐wave coupling generation mechanism is further confirmed by another two simulations, where two or three pump magnetosonic waves are initially injected. The lower‐frequency waves, that is, the fundamental wave and its second harmonic, are also successfully reproduced due to the nonlinear coupling of pump magnetosonic waves. Our simulations not only propose a potential generation mechanism of unusual lower harmonic magnetosonic waves in the Earth's magnetosphere, but also give some new insights on the evolution of magnetosonic spectra. |
| format | Article |
| id | doaj-art-83f90aa6cfd64359a6f5bec25eb3da1e |
| institution | OA Journals |
| issn | 0094-8276 1944-8007 |
| language | English |
| publishDate | 2018-08-01 |
| publisher | Wiley |
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| series | Geophysical Research Letters |
| spelling | doaj-art-83f90aa6cfd64359a6f5bec25eb3da1e2025-08-20T01:58:00ZengWileyGeophysical Research Letters0094-82761944-80072018-08-0145168029803410.1029/2018GL079090Generation of Lower Harmonic Magnetosonic Waves Through Nonlinear Wave‐Wave InteractionsXinliang Gao0Jicheng Sun1Quanming Lu2Lunjin Chen3Shui Wang4CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Science University of Science and Technology of China Hefei ChinaCAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Science University of Science and Technology of China Hefei ChinaCAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Science University of Science and Technology of China Hefei ChinaDepartment of Physics University of Texas at Dallas Richardson TX USACAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Science University of Science and Technology of China Hefei ChinaAbstract Although magnetosonic waves in the Earth's magnetosphere have been well understood by the linear theory, low harmonic magnetosonic waves, which often lack of free energy, can be unusually present. By employing a 1‐D particle‐in‐cell simulation model, we have investigated the generation of those unusual lower harmonic magnetosonic waves in a plasma containing a proton ring distribution. In our simulation, the higher harmonic magnetosonic waves (from~9Ωh to ~12Ωh) are firstly excited due to the unstable proton ring, which can be well explained by the linear theory. Several lower harmonic magnetosonic waves (below 5Ωh), which well separates away from the higher harmonics, soon appear in the system. Those lower harmonics, which do not have any positive linear growth rates, can be generated by a nonlinear mechanism. The bicoherence analysis demonstrates that there is a strong phase coupling among the unusual lower harmonic magnetosonic waves and the magnetosonic waves generated due to the proton ring, supporting the idea that the lower harmonic waves could be driven by the wave‐wave couplings of the generated magnetosonic waves. This wave‐wave coupling generation mechanism is further confirmed by another two simulations, where two or three pump magnetosonic waves are initially injected. The lower‐frequency waves, that is, the fundamental wave and its second harmonic, are also successfully reproduced due to the nonlinear coupling of pump magnetosonic waves. Our simulations not only propose a potential generation mechanism of unusual lower harmonic magnetosonic waves in the Earth's magnetosphere, but also give some new insights on the evolution of magnetosonic spectra.https://doi.org/10.1029/2018GL079090magnetosonic waveslower harmonicwave–wave couplingPIC simulationsmagnetosphere |
| spellingShingle | Xinliang Gao Jicheng Sun Quanming Lu Lunjin Chen Shui Wang Generation of Lower Harmonic Magnetosonic Waves Through Nonlinear Wave‐Wave Interactions Geophysical Research Letters magnetosonic waves lower harmonic wave–wave coupling PIC simulations magnetosphere |
| title | Generation of Lower Harmonic Magnetosonic Waves Through Nonlinear Wave‐Wave Interactions |
| title_full | Generation of Lower Harmonic Magnetosonic Waves Through Nonlinear Wave‐Wave Interactions |
| title_fullStr | Generation of Lower Harmonic Magnetosonic Waves Through Nonlinear Wave‐Wave Interactions |
| title_full_unstemmed | Generation of Lower Harmonic Magnetosonic Waves Through Nonlinear Wave‐Wave Interactions |
| title_short | Generation of Lower Harmonic Magnetosonic Waves Through Nonlinear Wave‐Wave Interactions |
| title_sort | generation of lower harmonic magnetosonic waves through nonlinear wave wave interactions |
| topic | magnetosonic waves lower harmonic wave–wave coupling PIC simulations magnetosphere |
| url | https://doi.org/10.1029/2018GL079090 |
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