The nonlinear evolution of whistler-mode chorus: modulation instability as the source of tones
The nonlinear evolution of whistler-mode chorus: modulation instability as the source of tones
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DOI：
10.1017/s0022377823001265
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发表时间：
2023-05
影响因子：
2.5
通讯作者：
D. Ratliff;O. Allanson
中科院分区：
文献类型：
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作者：
D. Ratliff;O. Allanson
我们从形式角度回顾了在温暖等离子体中传播的平行传播/场对准口哨模式合唱（WMC）波的调制稳定性，重点关注通过有质动力的波粒相互作用。调制不稳定性标准的特征在于哨声模式波的群速度色散 $d c_g/dk$ 以及群速度 $c_g$ 与电子声速 $c_{s,e}$ 之间的比率条件。我们还证明，为了研究包膜的时空演化和包的形成（根据这一机制），必须考虑系统内离子的运动，从而导致离子对由等离子体的离子分数确定的调制不稳定性阈值的影响。最后，我们证明，当幅度的时空演化中包含高阶效应时，可以捕获啁啾。这不仅产生了扫描速率的明确表达式，而且还确定了在电子陀螺频率一半处出现的功率带隙的可能起源。数值验证表明，波包之间的相互作用是任务数据中观察到的音调出现的来源，并且这种相互作用可能是 WMC 负责的电子能量的主要来源。
We review the modulation stability of parallel-propagating/field-aligned whistler-mode chorus (WMC) waves propagating in a warm plasma from a formal perspective with a focus on wave–particle interactions via ponderomotive forces. The modulation instability criteria are characterised by the group velocity dispersion, $d c_g/dk$, for whistler-mode waves and a condition on the ratio between the group velocity $c_g$ and the electron sound speed $c_{s,e}$. We also demonstrate that in order to investigate the spatiotemporal evolution of the envelope and the formation of packets (according to this mechanism), one necessarily needs to account for the motion of ions within the system, leading to an ionic influence on the modulation instability threshold determined by the ion fraction of the plasma. Finally, we demonstrate that chirping may be captured when higher-order effects are included within the spatiotemporal evolution of the amplitude. This yields not only an explicit expression for the sweep rate but also identifies a possible origin for the power band gap that occurs at half the electron gyrofrequency. Numerical validation demonstrates that the interaction between wave packets is a source for the emergence of tones observed within mission data, and such interactions may be a major source of the electron energisation which WMC are responsible for.