GEM: From the Micro to the Macro--Identifying the Mechanisms Responsible for Megaelectron-Volt (MeV) Electron Microbursts and Quantifying Their Role in Global Radiation Belt Losses

地球辐射带的动力学演化受粒子被加速并进入磁层和从磁层消失之间的相对平衡控制。相对论性电子微暴流是磁层中粒子损失的一个来源。这项工作是一个建模的努力，以更好地了解从微下击暴流损失的物理过程。这项工作将对支持我们社会和国家安全的技术基础设施产生更广泛的影响，因为辐射带电子对地球轨道航天器构成重大的空间天气危害。将支助两名本科生和一名研究生，努力开发一个计算框架，以确定在地球外辐射带产生相对论性电子微暴流的物理机制，并首次量化这一散射过程造成的准确损失估计。科学调查将按以下方式进行。数值射线追踪将用于计算作为时间和沿着给定磁场线位置的函数的合唱波功率谱（频率和波法线角），包括朗道阻尼。然后，波功率分布将用于计算由于与所获得的合唱波场的共振相互作用（包括非线性效应）而导致的沿沿着场线的每个点处的损失锥附近的合成俯仰角变化。然后对一组测试粒子重复这一过程（即，高能电子）在初始能量范围内。对于一个假设的辐射带电子分布采取的经验模型，工作计算的时空依赖性的电子通量沉淀到电离层由于派生的共振俯仰角散射。在一系列位置重复这整个过程，提供了沉淀到电离层中的电子通量的地图，作为时间，位置和能量的函数，由于与合唱波的共振相互作用。这些模型计算在手，工作探索和评估的各种潜在的机制，通过参数变化，例如通过增加/抑制朗道阻尼，或通过限制/包括高阶共振散射。这些机制，然后将通过数据模型比较，统计和个别事件的额外审查。这个奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的知识价值和更广泛的影响审查标准。

The dynamical evolution of the Earth’s radiation belts is governed by the relative balance between particles being accelerated and transported into and lost from the magnetosphere. Relativistic electron microbursts are one source of particle losses in the magnetosphere. This work is a modeling effort to better understand the physical process of losses from microbursts. The work will have a broader impact on the technological infrastructure that supports our society and national security, due to the significant space weather hazard that radiation belt electrons pose to Earth-orbiting spacecraft. Two undergraduates and one graduate student researcher will be supported.The effort will develop a computational framework to identify the physical mechanisms that produce relativistic electron microbursts in the Earth’s outer radiation belt and to quantify, for the first time, accurate loss estimates due to this scattering process. The science investigation will be carried out as follows. Numerical ray tracing will be used to calculate the chorus wave power spectrum (frequency and wave normal angle) as a function of time and location along a given magnetic field line, including Landau damping. Then, the wave power distribution will be used to calculate the resultant pitch-angle change near the loss cone at each point along the field line due to resonant interactions with the obtained chorus wave field, including nonlinear effects. This is then repeated for a set of test-particles (i.e., energetic electrons) over a range of initial energies. For an assumed radiation belt electron distribution taken from an empirical model, the work calculates the spatio-temporal dependence of the electron flux precipitated into the ionosphere due to the derived resonant pitch-angle scattering. Repeating this entire procedure across a range of locations provides a map of the electron flux precipitated into the ionosphere as a function of time, position, and energy, due to resonant interactions with chorus waves. With these model calculations in hand, the work explores and evaluates the various potential mechanisms involved in the scattering through parameter variation, for example by increasing/suppressing Landau damping, or by restricting/including higher order resonances. These mechanisms will then be additionally scrutinized through data-model comparisons, both statistical and for an individual event.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.