Radiation belt electrons undergo frequent acceleration, transport, and loss processes under various physical mechanisms. One of the most prevalent mechanisms is radial diffusion, caused by the resonant interactions between energetic electrons and ULF waves in the Pc4-5 band. An indication of this resonant interaction is believed to be the appearance of periodic flux oscillations. In this study, we report long-lasting, drift-periodic flux oscillations of relativistic and ultrarelativistic electrons with energies up to ∼7.7 MeV in the outer radiation belt, observed by the Van Allen Probes mission. During this March 2017 event, multi-MeV electron flux oscillations at the electron drift frequency appeared coincidently with enhanced Pc5 ULF wave activity and lasted for over 10 h in the center of the outer belt. The amplitude of such flux oscillations is well correlated with the radial gradient of electron phase space density (PSD), with almost no oscillation observed near the PSD peak. The temporal evolution of the PSD radial profile also suggests the dominant role of radial diffusion in multi-MeV electron dynamics during this event. By combining these observations, we conclude that these multi-MeV electron flux oscillations are caused by the resonant interactions between electrons and broadband Pc5 ULF waves and are an indicator of the ongoing radial diffusion process during this event. They contain essential information of radial diffusion and have the potential to be further used to quantify the radial diffusion effects and aid in a better understanding of this prevailing mechanism.

中文翻译：

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范艾伦在 2017 年 3 月事件期间对地球外辐射带中多 MeV 电子漂移周期通量振荡的观测

辐射带电子在各种物理机制下经历频繁的加速、传输和丢失过程。最普遍的机制之一是径向扩散，由 Pc4-5 波段中高能电子和 ULF 波之间的共振相互作用引起。这种共振相互作用的迹象被认为是周期性通量振荡的出现。在这项研究中，我们报告了由范艾伦探测器任务观察到的外辐射带中能量高达 ~7.7 MeV 的相对论和超相对论电子的长期漂移周期性通量振荡。在 2017 年 3 月的这次事件中，电子漂移频率下的多 MeV 电子通量振荡与增强的 Pc5 ULF 波活动同时出现，并在外带中心持续了 10 多个小时。这种通量振荡的幅度与电子相空间密度 (PSD) 的径向梯度密切相关，在 PSD 峰值附近几乎没有观察到振荡。PSD 径向剖面的时间演变也表明径向扩散在此事件期间在多 MeV 电子动力学中的主导作用。通过结合这些观察，我们得出结论，这些多 MeV 电子通量振荡是由电子和宽带 Pc5 ULF 波之间的共振相互作用引起的，并且是该事件期间正在进行的径向扩散过程的指标。它们包含径向扩散的基本信息，有可能被进一步用于量化径向扩散效应，并有助于更好地理解这种普遍的机制。