Electron Diffusion and Advection During Nonlinear Interactions With Whistler-Mode Waves
Electron Diffusion and Advection During Nonlinear Interactions With Whistler-Mode Waves
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DOI：
10.1029/2020ja028793
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发表时间：
2021-05-01
影响因子：
2.8
通讯作者：
Ratcliffe, H.
中科院分区：
文献类型：
--
作者：
Allanson, O.;Watt, C. E. J.;Ratcliffe, H.
辐射带代码演变电子动力学由于共振波粒子相互作用。目前还不知道如何最好地将电子动力学的波功率谱的情况下，变化相当大的“子网格”的时间尺度短于计算的时间步长的辐射带模型Δ t（RBM），特别是如果波的振幅达到高值。与热不稳定性增长率相关的时间尺度非常短，通常比Delta t（RBM）短得多。我们使用一个动力学代码来研究电子相互作用的哨声模式波的存在下，热各向异性的背景。对于各向异性的"低"值，不稳定性不会被触发，我们观察到与Allanson等人（2020，）中获得的结果相似的结果，其中扩散在短时间尺度上大致匹配准线性理论。对于"高"水平的各向异性，通过不稳定性的波增长被触发。当用平均波功率计算时，拟线性理论不能很好地描述动力学。强电子扩散和平流发生在生长阶段（约100毫秒）。这些动态"饱和"的波功率饱和在接近1 nT，和平流运动占主导地位的扩散过程。生长阶段通过与不同频率的波的连续共振相互作用促进俯仰角空间中的显著平流。我们认为，这种快速平流运输波的增长阶段可能有一个作用，发挥电子微暴流机制。这激发了未来对辐射带建模中短时间尺度非线性过程宏观影响的研究。
Radiation belt codes evolve electron dynamics due to resonant wave-particle interactions. It is not known how to best incorporate electron dynamics in the case of a wave power spectrum that varies considerably on a "sub-grid" timescale shorter than the computational time-step of the radiation belt model Delta t(RBM), particularly if the wave amplitude reaches high values. Timescales associated with the growth rate of thermal instabilities are very short, and are typically much shorter than Delta t(RBM). We use a kinetic code to study electron interactions with whistler-mode waves in the presence of a thermally anisotropic background. For "low" values of anisotropy, instabilities are not triggered and we observe similar results to those obtained in Allanson et al. (2020, ), for which the diffusion roughly matched the quasilinear theory over short timescales. For "high" levels of anisotropy, wave growth via instability is triggered. Dynamics are not well described by the quasilinear theory when calculated using the average wave power. Strong electron diffusion and advection occur during the growth phase (approximate to 100 ms). These dynamics "saturate" as the wave power saturates at approximate to 1 nT, and the advective motions dominate over the diffusive processes. The growth phase facilitates significant advection in pitch angle space via successive resonant interactions with waves of different frequencies. We suggest that this rapid advective transport during the wave growth phase may have a role to play in the electron microburst mechanism. This motivates future work on macroscopic effects of short-timescale nonlinear processes in radiation belt modeling.