Triggering process of whistler-mode chorus emissions in the magnetosphere
Triggering process of whistler-mode chorus emissions in the magnetosphere
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DOI：
10.1109/ursigass.2011.6051074
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发表时间：
2011-05
期刊：
影响因子：
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通讯作者：
Y. Omura;D. Nunn
中科院分区：
文献类型：
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作者：
Y. Omura;D. Nunn
合唱发射是由磁层中高能电子（10-100 keV）的温度各向异性驱动的线性回旋不稳定性触发的。由于在速度空间中存在电磁电子空穴，在磁赤道附近，合唱发射作为一种绝对非线性不稳定性而增长。从恒定频率的线性波生长到音调频率上升的非线性波生长的转变过程是由于形成了与波磁场反平行的谐振电流- JB。升音频率使赤道电子空穴发生相移，产生与波电场反平行的谐振电流分量，引起波的非线性生长。为了证实这一触发机制，我们进行了有JB和没有JB的Vlasov混合仿真。没有JB的跑步不会复制合唱排放，而有JB的跑步确实成功地复制了合唱排放。由JB引起的非线性频移ω1在触发过程中起着关键作用。发现频移的非线性跃迁时间TN与非线性捕获周期具有相同的量级，仿真和观测证实了这一点。确定的扫频率为ω1 / TN，给出了和声发射的最佳波幅。
Chorus emissions are triggered from the linear cyclotron instability driven by the temperature anisotropy of energetic electrons (10–100 keV) in the magnetosphere. Chorus emissions grow as an absolute nonlinear instability near the magnetic equator due to the presence of an electromagnetic electron hole in velocity space. The transition process from the linear wave growth at a constant frequency to the nonlinear wave growth with a rising tone frequency is due to formation of a resonant current — JB anti-parallel to the wave magnetic field. The rising-tone frequency introduces a phase shift to the electron hole at the equator, and results in a resonant current component anti-parallel to the wave electric field — JE, which causes the nonlinear wave growth. To confirm this triggering mechanism, we perform Vlasov Hybrid Simulations with JB and without JB. The run without JB does not reproduce chorus emissions, while the run with JB does successfully reproduce chorus emissions. The nonlinear frequency shift ω1 due to JB plays a critical role in the triggering process. The nonlinear transition time TN for the frequency shift is found to be of the same order as the nonlinear trapping period, which is confirmed by simulations and observation. The established frequency sweep rate is ω1 / TN, which gives an optimum wave amplitude of chorus emissions.