Collaborative Research: GEM: Plasma Sheet Instabilities prior to THEMIS Substorm Expansion Onsets

该项目对地球空间环境模拟工作重点小组关于磁层亚暴开始的早期阶段作出了贡献。它将系统地分析爆发前的近地等离子床亚风暴事件的等离子体不稳定性。等离子体片条件将用OpenGGCM MHD程序通过磁流体力学模拟来重建。一旦知道了等离子体膜的结构，就有可能检查结构对宏观不稳定性的稳定性，如气球、扭结和撕裂模式。稳定性分析将采用解析特征值法和MHD模拟两种方法。该项目将检查等离子体不稳定性的特征和后果，并将结果与NASA THEMIS任务的观测结果进行比较。亚暴发展阶段等离子体膜的线性不稳定性和早期非线性不稳定性是理解亚暴爆发初期的关键。稳定性分析的准确性依赖于对等离子体片构型模型的详细了解。亚暴观测将提供更多的输入条件和约束，使OpenGGCM模拟能够在亚暴增长阶段重建一系列准确和真实的等离子体片配置。稳定性分析将有助于解决关于亚暴爆发过程的许多剩余争议，并为亚暴爆发问题带来新的视角。该项目将有助于对THEMIS亚风暴事件提供定量解释，并将弥合理论、分析和观测之间的差距。

This project contributes to the Geospace Environment Modeling (GEM) Focus Group on the early stages of the onset of a magnetospheric substorm. It will systematically analyze the plasma instabilities of the pre-onset, near-Earth plasmasheet substorm events. The plasma sheet conditions will be reconstructed using magnetohydrodynamic simulations with the OpenGGCM MHD code. Once the plasmasheet configuration is known, it will be possible to examine the stability of the configuration to macroscale instabilities such as ballooning, kink, and tearing modes. Both analytical eigenvalue methods and MHD simulations will be used in the stability analysis. The project will examine the signatures and consequences of the plasma instabilities and compare the results with observations made by the NASA THEMIS mission. The linear and early nonlinear instabilities of the plasmasheet during substorm growth phase are the keys to understanding the initial stage of the substorm expansion onset. The accuracy of the stability analyses relies on the detailed knowledge of the plasma sheet configuration model. THEMIS substorm observations will provide more input conditions and constraints that will enable the OpenGGCM simulation to reconstruct a sequence of accurate and realistic plasma sheet configurations during the substorm growth phase. The stability analysis will help resolve many remaining controversies on the onset process and bring in new perspectives on the substorm onset problem. The project will help provide quantitative interpretation of THEMIS substorm events, and will bridge the gap between theory, analysis and observations.