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 Δt_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 Δt_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, https://doi.org/10.1029/2020JA027949), 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 (≈100 ms). These dynamics “saturate” as the wave power saturates at ≈ 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.

中文翻译：

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惠斯勒模式波非线性相互作用中的电子扩散和对流

辐射带代码由于共振波粒子相互作用而发展出电子动力学。在波能谱在比辐射带模型Δt _RBM的计算时间步长短的“子网格”时间尺度上发生显着变化的波功率谱的情况下，如何将电子动力学最佳地结合尚不清楚，特别是在波幅较大的情况下达到很高的价值。与热不稳定性的增长速率相关的时间尺度非常短，并且通常比Δt _RBM短得多. 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, https://doi.org/10.1029/2020JA027949), 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 (≈100 ms). These dynamics “saturate” as the wave power saturates at ≈ 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.