合唱波的“捕获-释放-放大”模型
A "Trap-Release-Amplify" Model of Chorus Waves
摘要：
哨声模式合唱波是具有频率啁啾的准相干电磁辐射。啁啾机制是空间等离子体中一个长期存在的问题，人们提出了各种各样的模型来理解啁啾机制。在分析自洽粒子模拟中有效波增长率和电子相空间动力学的基础上，提出了一个合唱现象的“捕获-释放-放大”（TaRA）模型.在该模型中，关联电子的相空间结构是由非线性波粒子相互作用形成的，这种相互作用主要发生在下游。当从上游的波包释放时，这些电子选择性地放大满足锁相条件的新发射，以最大化波功率传输，从而导致频率啁啾。在释放点的锁相条件给出的频率啁啾率是完全一致的一个由Helliwell在一个不均匀的背景磁场的情况下。TaRA模型的非线性波粒子相互作用部分导致啁啾率与波振幅成比例，这是Vomvortian等人最初得出的结论。因此，TaRA模型统一了看似无关的研究中的两个不同结果。此外，TaRA模型自然地解释了合唱波的精细结构，包括子包和带宽，以及它们通过相位捕获电子动力学的演化。最后，我们建议这个模型可以用来解释其他相关的现象，包括频率啁啾的合唱团在一个均匀的背景磁场和电磁离子回旋波在磁层。
英文摘要：
Whistler mode chorus waves are quasi-coherent electromagnetic emissions with frequency chirping. Various models have been proposed to understand the chirping mechanism, which is a long-standing problem in space plasmas. Based on analysis of effective wave growth rate and electron phase space dynamics in a self-consistent particle simulation, we propose here a phenomenological model called the "Trap-Release-Amplify" (TaRA) model for chorus. In this model, phase space structures of correlated electrons are formed by nonlinear wave particle interactions, which mainly occur in the downstream. When released from the wave packet in the upstream, these electrons selectively amplify new emissions which satisfy the phase-locking condition to maximize wave power transfer, leading to frequency chirping. The phase-locking condition at the release point gives a frequency chirping rate that is fully consistent with the one by Helliwell in case of a nonuniform background magnetic field. The nonlinear wave particle interaction part of the TaRA model results in a chirping rate that is proportional to wave amplitude, a conclusion originally reached by Vomvoridis et al. Therefore, the TaRA model unifies two different results from seemingly unrelated studies. Furthermore, the TaRA model naturally explains fine structures of chorus waves, including subpackets and bandwidth, and their evolution through dynamics of phase-trapped electrons. Finally, we suggest that this model could be applied to explain other related phenomena, including frequency chirping of chorus in a uniform background magnetic field and of electromagnetic ion cyclotron waves in the magnetosphere.
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