The nonlinear evolution of whistler-mode chorus: modulation instability as the source of tones

IF 2.1 3区 物理与天体物理 Q2 PHYSICS, FLUIDS & PLASMAS
Daniel J. Ratliff, Oliver Allanson
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Abstract

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, $d c_g/dk$Abstract Image, for whistler-mode waves and a condition on the ratio between the group velocity $c_g$Abstract Image and the electron sound speed $c_{s,e}$Abstract Image. 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.

啸叫模式合唱的非线性演化:作为音源的调制不稳定性
我们从形式的角度回顾了在暖等离子体中传播的平行传播/场对齐的惠斯勒模式合唱波(WMC)的调制稳定性,重点是通过深思动力的波粒相互作用。调制不稳定性标准的特征是惠斯勒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,为了研究包络的时空演变和数据包的形成(根据这一机制),必须考虑系统内离子的运动,从而导致离子对调制不稳定性阈值的影响,该阈值由等离子体中的离子比例决定。最后,我们证明,如果将高阶效应纳入振幅的时空演变中,就可以捕捉到啁啾现象。这不仅得到了扫频的明确表达式,而且还确定了在电子回旋频率的一半出现功率带间隙的可能原因。数值验证表明,波包之间的相互作用是在任务数据中观测到的音调出现的一个来源,这种相互作用可能是 WMC 导致的电子通电的一个主要来源。
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来源期刊
Journal of Plasma Physics
Journal of Plasma Physics 物理-物理:流体与等离子体
CiteScore
3.50
自引率
16.00%
发文量
106
审稿时长
6-12 weeks
期刊介绍: JPP aspires to be the intellectual home of those who think of plasma physics as a fundamental discipline. The journal focuses on publishing research on laboratory plasmas (including magnetically confined and inertial fusion plasmas), space physics and plasma astrophysics that takes advantage of the rapid ongoing progress in instrumentation and computing to advance fundamental understanding of multiscale plasma physics. The Journal welcomes submissions of analytical, numerical, observational and experimental work: both original research and tutorial- or review-style papers, as well as proposals for its Lecture Notes series.
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