Collaborative Research: GEM--Energetic Electron Nonlinear Interactions with Oblique Whistler-Mode Chorus Waves

惠斯勒模式的“合唱”波是地球外辐射带自然产生的无线电发射。这些波可以与捕获的高能电子（~10 keV到1 MeV）共振相互作用，既将它们加速到高速，又以“粒子沉淀”的形式将它们散射到大气中。强烈的合唱波以斜角向背景磁场传播，以多重谐波引发这种共振，并在几十秒内快速产生强烈的电子响应。然而，不同的共振谐波在形成辐射带的全球状态中的作用仍然未知。这项研究将研究电子和这些强烈的斜合唱波之间的相互作用来解决这个问题。了解这些过程的性质和机制对于预测空间天气及其对敏感系统（如航天器表面和电子设备）的影响非常重要。该项目还将支持早期职业科学家和一名研究生，研究结果将被纳入德克萨斯大学达拉斯分校的公共宣传材料和本科生课程中。这个项目的目标是解决三个具体的科学问题：1)在斜哨声模式合唱波的非线性波粒相互作用下，高能电子相空间密度是如何演变的？2)不同的电子谐波共振与磁层合唱波之间是否存在可观察到的区别，如果有，它们是什么？3)朗道共振和回旋加速器共振在强斜合唱波事件中对外辐射带形成的作用是什么？为了回答这些问题，研究人员将开发斜合唱波包和电子相空间密度演变的数值模型，并将模型结果与美国宇航局范艾伦探测器的原位测量结果进行定量比较。重要的是，这项研究可能会导致在包括朗道共振在内的特殊谐波中发现电子非线性共振的直接观测证据。这些重要的过程已经在理论上发生在外太空，但尚未得到实验证据的证实。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Whistler-mode "chorus" waves are naturally occurring radio emissions in Earth's outer radiation belt. These waves can resonantly interact with trapped energetic electrons (~10 keV to 1 MeV), both accelerating them to high speeds and scattering them into the atmosphere as "particle precipitation." Intense chorus waves, propagating at oblique angles to the background magnetic field, invoke such resonances in multiple harmonics and produce strong electron responses on rapid timescales, within tens of seconds. However, the role of different resonance harmonics in shaping the global state of the radiation belt remains unknown. This investigation will study the interactions between electrons and these intense oblique chorus waves to address this problem. Understanding the properties and mechanisms of these processes is important for forecasting space weather and its effects on sensitive systems, such as spacecraft surfaces and electronics. This project will also support early-career scientists and a graduate student, and the findings will be incorporated into public outreach materials and undergraduate classes at the University of Texas at Dallas.The goal of this project is to address three specific scientific questions: 1) How does energetic electron phase space density evolve under nonlinear wave-particle interactions with oblique whistler-mode chorus waves? 2) Are there observable distinctions between different electron harmonic resonances with magnetospheric chorus waves and, if so, what are they? 3) What are the respective roles of Landau and cyclotron resonances in shaping the outer radiation belt in events with intense oblique chorus waves? To answer these questions, the investigators will develop numerical models of both oblique chorus wave packets and electron phase space density evolution, and quantitatively compare model results with in-situ measurements made by NASA's Van Allen Probes. Importantly, this research may lead to the discovery of direct observational evidence of electron nonlinear resonances in distinctive harmonics, including Landau resonance. These important processes have been theorized to occur in outer space but have yet to be confirmed with experimental evidence.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.