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

在环绕地球的辐射带中，电子被加速到极端相对论的速度。这个过程是如何发生的，是一个根本的悬而未决的问题。该项目涉及两种主要加速机制的相对重要性，即向内径向扩散和局部加速。利用一种新的计算径向扩散系数的方法，本研究将量化径向扩散对超相对论电子加速的贡献及其对电子能量的依赖。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》规定的一项优先事项。这个项目使用了一种新的方法来计算特定事件的径向扩散系数，并量化径向扩散在外辐射带中心(L~3-6)极端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，结合粒子跟踪模拟，将根据选定事件期间被跟踪粒子的径向位移计算径向扩散系数。结合Fokker-Planck方程的径向扩散模型，我们将量化径向扩散在极端相对论电子加速中的贡献，并揭示其对电子能量的依赖关系。具体来说，将回答以下科学问题：(I)极端相对论电子的周期性通量振荡多久发生一次？不同能量的极端相对论电子的径向扩散系数是多少？(Ii)对于选定的电子通量增强事件，从定量上讲，径向扩散对外带中心的超相对论电子加速(L~3-6)有什么作用？(三)径向扩散对外带中心超相对论电子加速的相对贡献如何随着电子能量的变化而变化？这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.