GEM: Multi-scale Empirical Geomagnetic Field Modeling

几十年来，从太空仪器收集的数据建立了复杂的地球磁场经验模型。这些模型是对基于物理的第一原理模型的必要补充。该项目的目标是改进磁层的经验模型，使其包括较长的太阳周期时间尺度和较短的亚风暴时间尺度。这将极大地提高对近地环境的了解，这对最终保护现代技术非常重要。这项工作将促进研究生和暑期学生的实践研究训练。本项目是对风暴尺度经验地磁场TS07D模型进行根本性升级，使其包括比风暴更长和更短时间尺度的地磁变化。前者是由太阳辐射（以F10.7通量量化）的太阳周期变化引起的。后者代表由极光指数量化的亚暴效应。这项工作将解决太阳辐照度对地磁场结构和潜在电流系统的影响，以及亚暴变薄和磁尾的双极化如何影响地磁场的经验图像。新的模型升级旨在回答这些问题，采用了具有不同电流片厚度值的赤道电流的多次扩展，以及改进的场对准电流系统描述。它将系统科学方法与物理方法相结合，在经验重构磁层几个全局参数的演化过程中，对经验模型的时空尺度和结构进行约束。

Sophisticated empirical models of the Earth's magnetic field have been built over decades of data collected from spaceborne instruments. These models are a necessary compliment to the physics-based first-principles models. The project goals are to improve one such empirical model of the magnetosphere to include longer, solar cycle time scales and shorter, substorm time scales. This will vastly improve understanding of the near-Earth environment, which is important for ultimately protecting modern technology. The effort will promote hands-on research training for a graduate student and a summer student.This project is to fundamentally upgrade the storm-scale empirical geomagnetic field TS07D model to include geomagnetic variations on time scales both longer and shorter than those of storms. The former are caused by the solar cycle variations of the solar radiation (quantified by the F10.7 flux). The latter represent substorm effects quantified by auroral indices. The work will address what the impact of the solar irradiance on the structure of the geomagnetic field and underlying current system is, and how substorm thinning and dipolarization of the magnetotail affect the empirical picture of the geomagnetic field. The new model upgrade, which is aimed to answer these questions, employs multiple expansions of equatorial currents with different current sheet thickness values as well as an improved description of the field aligned current system. It combines the system science approach, when the evolution of a few global parameters of the magnetosphere is reconstructed empirically, with the physics-based approach, which is used to constrain spatio-temporal scales and structure of the empirical model.