GEM: Quantifying the Role of Radial Diffusion on the Energy-dependent Acceleration of Ultrarelativistic Electrons in the Center of Outer Radiation Belt

GEM：量化径向扩散对外辐射带中心超相对论电子依赖能量的加速的作用

• 批准号: 1952903
• 负责人: Hong Zhao
• 金额: $ 34.73万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-03-01 至 2021-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1952903&HistoricalAwards=false
• 关键词: GEM; Quantifying; Role; Radial; Diffusion

In the radiation belts surrounding the Earth, electrons are accelerated to ultrarelativistic speeds. How this process occurs is a fundamental unanswered question. The project addresses the relative importance of two main acceleration mechanisms, inward radial diffusion and local acceleration. Using a novel approach to calculate the radial diffusion coefficients, this study will quantify the contribution from radial diffusion to ultrarelativisitic electron acceleration and its dependence on electron energy. The results of this project will contribute to updating space weather forecast models, which is a priority set out in the National Space Weather Action Plan. An early career researcher and an undergraduate student will receive support.This project uses a novel approach to calculate event-specific radial diffusion coefficients and quantify the role of radial diffusion in ultrarelativistic electron acceleration in the center of the outer radiation belt (L~3 – 6). Using observations of electron flux oscillations and electric/magnetic fields, combined with particle-tracing simulations, the radial diffusion coefficients will be calculated from the radial displacement of the traced particles during selected events. Combining with the radial diffusion model using the Fokker-Planck equation, the contribution of radial diffusion in the ultrarelativistic electron acceleration will be quantified, and its dependence on electron energy will be revealed. Specifically, the following science questions will be answered: (i.) How often do the ultrarelativistic electron periodic flux oscillations occur and what are the associated radial diffusion coefficients for ultrarelativistic electrons with different energies? (ii.) For selected electron flux enhancement events, quantitatively, what is the role of radial diffusion to the ultrarelativistic electron acceleration in the center of outer belt (L~3 – 6)? (iii.) How does the relative contribution of radial diffusion to the ultrarelativistic electron acceleration in the center of outer belt vary with electron energy?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.

在地球周围的辐射带中，电子被加速到超相对论速度。这个过程是如何发生的是一个基本的未回答的问题。该项目涉及两个主要加速机制的相对重要性，向内径向扩散和局部加速。使用一种新的方法来计算径向扩散系数，这项研究将量化的贡献，从径向扩散超相对论电子加速和它的依赖于电子能量。该项目的成果将有助于更新空间气象预报模型，这是《国家空间气象行动计划》中规定的一个优先事项。本项目采用一种新的方法计算事件特异性径向扩散系数，并量化径向扩散在外辐射带中心（L3 - 6）的超相对论电子加速中的作用。利用对电子通量振荡和电场/磁场的观测，结合粒子追踪模拟，将根据选定事件期间追踪粒子的径向位移计算径向扩散系数。结合基于Fokker-Planck方程的径向扩散模型，对径向扩散在超相对论电子加速中的贡献进行了定量分析，并揭示了径向扩散对电子能量的依赖关系。具体而言，将回答以下科学问题：（一）超相对论电子周期性通量振荡发生的频率是多少？不同能量的超相对论电子的径向扩散系数是多少？（二）对于选定的电子通量增强事件，在定量上，径向扩散对外带中心（L3 - 6）的超相对论电子加速的作用是什么？（三）径向扩散对外带中心超相对论电子加速的相对贡献随电子能量的变化如何？该奖项反映了NSF的法定使命，并被认为是值得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的支持。

项目成果

On the Association Between Electron Flux Oscillations and Local Phase Space Density Gradients

• DOI: 10.1029/2020ja028891
• 发表时间: 2021-02
• 期刊: Journal of Geophysical Research: Space Physics
• 作者: T. Sarris;Xinlin Li;Hong Zhao;L. Khoo;Wenlong Liu;M. Temerin

Van Allen Probes Observations of Multi‐MeV Electron Drift‐Periodic Flux Oscillations in Earth's Outer Radiation Belt During the March 2017 Event

• DOI: 10.1029/2021ja029284
• 发表时间: 2021-07
• 期刊: Journal of Geophysical Research: Space Physics
• 作者: Hong Zhao;T. Sarris;Xinlin Li;Max Weiner;Isabela Huckabee;D. Baker;A. Jaynes;S. Kanekal;S. Elkington;M. Barani;W. Tu;Wenlong Liu;Dianjun Zhang;M. Hartinger