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

合作研究：GEM——量化离赤道超低频（ULF）波对辐射带径向扩散的贡献

• 批准号: 2247857
• 负责人: Hong Zhao
• 金额: $ 9万
• 依托单位: Auburn University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-06-01 至 2026-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2247857&HistoricalAwards=false
• 关键词: Collaborative; Research; GEM; Quantifying; Contribution

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.

已知具有超低频率（ULF）范围内频率的电磁波是径向扩散和地球辐射带中能量电子传输的主要原因之一。 ULF波的频率与能量电子的漂移频率旋转时的漂移频率范围重叠，从而导致了共鸣的相互作用。 已经得出了许多表达式来定量描述径向扩散，以便可以将它们纳入辐射带电子的整体模型中。 但是，径向扩散速率的大多数表达仅针对赤道反映电子，并且基于对从赤道平面附近或从地面接近的航天器获得的ULF波的功率的估计。 使用Van Allen探针和弧度的最新研究表明，磁波动中的波力显着增强了磁赤道，这与模拟磁层磁场线振荡模式的模型一致。 这对径向扩散速率的估计具有重要意义，因为较高的螺距角电子的ULF波波动比赤道电子更高。 该项目将得出磁性和电场波的功率，并将其纳入3D测试粒子模拟，以估计扩散系数。 新型的，倾斜角依赖性的扩散速率将被引入一个全局的辐射带电子模型，以评估扩散系数对辐射皮带动力学的俯仰角依​​赖性的影响。 该结果可能对目前估计的径向扩散率有重大影响。 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能量颗粒在辐射带的全局动力学上的俯仰角依​​赖性径向运输。将回答以下科学问题：在不同的太阳能和地磁条件下，ULF电场和磁场波动如何分布在磁性纬度和磁性局部时间？赤道ULF波波动在外部辐射带（L〜4至7）中相对论电子的径向扩散和运输的作用是什么？预期赤道ULF波如何影响当前的辐射带模型，它们对辐射带的全球动态有何贡献？ 该团队将使用多个卫星数据集（Themis，Van Allen探针，集群和弧度），测试粒子追踪模拟以及全球辐射带模型来量化非均程ULF浪潮对辐射带对辐射带的贡献，这是NSF的法定任务的审查，并通过评估了范围，这表明了NSF的法律范围的范围，并已被评估为范围。