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是由加速、进入和离开磁层的粒子之间的相对平衡所控制的。相对论性电子微爆发是磁层中粒子损失的一个来源。这项工作是为了更好地理解微爆损失的物理过程而进行的建模工作。由于辐射带电子对地球轨道航天器构成重大的空间天气危害，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。资助本科生2名，研究生1名。这项工作将开发一个计算框架，以确定在地球外辐射带产生相对论性电子微爆的物理机制，并首次量化由于这种散射过程造成的准确损失估计。科学调查将进行如下。数值射线追踪将用于计算合唱波功率谱（频率和波法向角）作为沿给定磁场线的时间和位置的函数，包括朗道阻尼。然后，将利用波功率分布计算由于与得到的合唱波场的共振相互作用（包括非线性效应）而导致的损失锥附近各点沿场线的最终俯角变化。然后在初始能量范围内对一组测试粒子（即高能电子）重复这一过程。对于从经验模型中获得的假设辐射带电子分布，本文计算了由于导出的共振俯仰角散射而沉淀到电离层的电子通量的时空依赖性。在一系列地点重复这整个过程，可以得到由于与合唱波的共振相互作用而沉淀到电离层的电子通量作为时间、位置和能量的函数的地图。有了这些模型计算，该工作探索和评估了通过参数变化参与散射的各种潜在机制，例如通过增加/抑制朗道阻尼，或通过限制/包括高阶共振。然后，这些机制将通过数据模型比较（包括统计数据和个别事件）进一步仔细检查。该奖项反映了美国国家科学基金会的法定使命，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。

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.