Collaborative Research: GEM--Quantifying the Contribution of Off-Equatorial Ultra-Low Frequency (ULF) Waves on Radial Diffusion in the Radiation Belts

频率在超低频（ULF）范围内的电磁波是地球辐射带中高能电子径向扩散和传输的主要原因之一。 超低频波的频率与高能电子绕地球飞行时的漂移频率范围重叠，导致共振相互作用。 已经推导出许多表达式来定量地描述径向扩散，以便它们可以被纳入辐射带电子的全球模型。 然而，大多数表达式的径向扩散率仅来自赤道镜像电子，并根据估计的超低频波的功率从航天器接近赤道平面或从地面获得。 最近使用货车艾伦探测器和Arase进行的研究表明，磁波动的波功率在远离磁赤道的地方显著增强，这与模拟磁层磁力线自然振荡模式的模型一致。 这对径向扩散率的估计具有重要意义，因为更高的俯仰角电子将经历比赤道电子高得多的ULF波波动。 该项目将导出磁场和电场波功率，并将其纳入3D测试粒子模拟中，以估计扩散系数。 新的，俯仰角依赖的扩散率将被引入到辐射带电子的全球模型，以评估辐射带动力学的扩散系数的俯仰角依赖性的效果。 这一结果可能对目前估计的径向扩散率产生重大影响。 该项目的主要目标是量化离赤道超低频（ULF）波对相对论电子径向输运和扩散的作用（100 s keV到几MeV）的辐射带（L~4到7），研究了高能粒子的俯仰角依赖的径向输运对辐射带全球动力学的影响。将回答以下科学问题：在不同的太阳和地磁条件下，超低频电场和磁场波动如何在磁纬度和磁地方时分布？在外辐射带（L~4 ~ 7）中，离赤道的超低频波动对外部辐射带（L~4 ~ 7）中相对论电子的径向扩散和输运有什么作用？离赤道的超低频波预计如何影响目前的辐射带模式，它们对辐射带的全球动力学有什么贡献？ 该团队将使用多个卫星数据集（THEMIS、货车艾伦探测器、Cluster和Arase）、测试粒子追踪模拟和全球辐射带模型来量化非赤道ULF波对辐射带径向扩散的贡献。该奖项反映了NSF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。

Electromagnetic waves with frequencies in the ultra-low frequency (ULF) range are known to be among the leading causes of radial diffusion and transport of energetic electrons in Earth's radiation belts. The frequencies of ULF waves overlap with the range of drift frequencies of energetic electrons as they circle the Earth, leading to resonant interactions. Numerous expressions have been derived to quantitatively describe radial diffusion so that they can be incorporated into global models of radiation belt electrons. However, most expressions of the radial diffusion rates are derived only for equatorially mirroring electrons and are based on estimates of the power of ULF waves that are obtained either from spacecraft close to the equatorial plane or from the ground. Recent studies using the Van Allen Probes and Arase have shown that the wave power in magnetic fluctuations is significantly enhanced away from the magnetic equator, consistent with models simulating the natural modes of oscillation of magnetospheric field lines. This has significant implications for the estimation of radial diffusion rates, as higher pitch angle electrons will experience considerably higher ULF wave fluctuations than equatorial electrons. This project will derive the magnetic and electric field wave powers and incorporate them into the 3D test particle simulations to estimate the diffusion coefficient. The novel, pitch-angle-dependent diffusion rates will be introduced to a global model of radiation belt electrons to evaluate the effect of the pitch-angle dependence of the diffusion coefficient on radiation belt dynamics. The result could have significant implications for the radial diffusion rates as currently estimated. It will pave the way for incorporating pitch-angle-dependent radial diffusion coefficients in global models to predict the near-Earth radiation environment better.The main goal of this project is to quantify the role of off-equatorial Ultra-Low Frequency (ULF) waves on the radial transport and diffusion of relativistic electrons (100s keV to few MeV) in the outer radiation belt (L~4 to 7), investigating the effect of pitch-angle-dependent radial transport of energetic particles on global dynamics of the radiation belts. The following science questions will be answered: How are ULF electric and magnetic field fluctuations distributed in magnetic latitude and magnetic local time under varying solar and geomagnetic conditions? What is the role of off-equatorial ULF wave fluctuations on the radial diffusion and transport of relativistic electrons in the outer radiation belt (L~4 to 7)? How are off-equatorial ULF waves expected to impact current radiation belt models, and what is their contribution to the global dynamics of the radiation belts? The team will use multiple satellite datasets (THEMIS, Van Allen Probes, Cluster, and Arase), test particle tracing simulations, and a global radiation belt model to quantify the contribution of off-equatorial ULF waves on radial diffusion in the radiation belts.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.