Nonlinear Interactions Between Radiation Belt Electrons and Chorus Waves: Dependence on Wave Amplitude Modulation
Nonlinear Interactions Between Radiation Belt Electrons and Chorus Waves: Dependence on Wave Amplitude Modulation
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DOI：
10.1029/2019gl085987
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发表时间：
2020-02-28
影响因子：
5.2
通讯作者：
Bortnik, J.
中科院分区：
文献类型：
--
作者：
Gan, L.;Li, W.;Bortnik, J.
我们使用测试粒子模拟来模拟辐射带电子和哨声模式合唱波之间的相互作用，重点是波的幅度调制。我们量化了具有不同初始能量和螺距角的电子由于相位捕获和相位聚束(包括平流和散射)而产生的螺距角和能量变化。在较宽的俯仰角-能量空间范围内，系统地识别了三个非线性区域，每个区域代表不同的非线性效应。我们的模拟结果表明，波幅调制可以扩展非线性区域，同时通过相位捕获显著降低电子加速度。通过引入幅度调制，减少了由位相聚束引起的俯仰角和能量的“平流”变化，同时增强了由位相聚束引起的“扩散”散射。我们的研究证明了波幅调制在非线性效应中的重要性，并建议将它们适当地纳入未来的理论和数值研究中。简单语言摘要惠斯勒模式合唱波是一种强烈的电磁辐射，对地球外辐射带中电子的俯仰角散射和加速起着重要作用。特别值得一提的是，大振幅的和声会导致与电子的非线性相互作用，即所谓的相位捕获和相位聚束。以前的研究表明，相位俘获可以快速加速电子，而相位聚束可以减速电子。然而，这种非线性相互作用的量化及其对合唱波幅度调制的依赖还没有完全被理解。在本文中，我们使用一组参数来量化在较宽的能量(0.01-10 MeV)和赤道俯仰角(0-90度)范围内和声与电子之间的非线性相互作用。我们发现，非线性相互作用导致了不同的螺距角和不同区域的能量变化。我们还发现，合唱波的幅度调制通常会减少非线性相互作用，其中相位捕获受到的影响最大。我们的研究表明，波幅调制的影响需要在未来的理论和数值研究中得到适当的考虑。
We use test particle simulations to model the interaction between radiation belt electrons and whistler mode chorus waves by focusing on wave amplitude modulations. We quantify the pitch angle and energy changes due to phase trapping and phase bunching (including both advection and scattering) for electrons with various initial energies and pitch angles. Three nonlinear regimes are identified in a broad range of pitch angle-energy space systematically, each indicating different nonlinear effects. Our simulation results show that wave amplitude modulations can extend the nonlinear regimes, while significantly reducing electron acceleration by phase trapping. By including amplitude modulations, the "advective" changes in pitch angle and energy caused by phase bunching are reduced, while the "diffusive" scattering due to phase bunching is enhanced. Our study demonstrates the importance of wave amplitude modulations in nonlinear effects and suggests that they need to be properly incorporated into future theoretical and numerical studies.Plain Language Summary Whistler mode chorus waves are intense electromagnetic emissions that play an important role in pitch angle scattering and acceleration of electrons in the Earth's outer radiation belt. Particularly, large amplitude chorus waves can result in nonlinear interactions with electrons, known as phase trapping and phase bunching. Previous studies have shown that phase trapping can accelerate electrons rapidly while phase bunching can decelerate electrons. However, quantification of such nonlinear interactions and their dependence on chorus wave amplitude modulations have not been fully understood. In this paper, we use a set of parameters to quantify the nonlinear interactions between chorus waves and electrons in a wide range of energy (0.01-10 MeV) and equatorial pitch angle (0-90 degrees). We found that nonlinear interactions lead to different pitch angle and energy variations at different regions of the pitch angle-energy space. We also found that nonlinear interactions are in general reduced by the amplitude modulations of chorus waves, with phase trapping being most significantly affected. Our study suggests that the effects of wave amplitude modulations need to be properly included in future theoretical and numerical studies.