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

该项目有助于地球空间环境模拟（GEM）焦点小组研究磁层亚暴发生的早期阶段。它将系统地分析近地等离子体亚暴事件发生前的等离子体不稳定性。利用OpenGGCM MHD代码进行磁流体动力学模拟，重建等离子体层条件。一旦等离子体结构已知，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。分析特征值法和MHD模拟都将用于稳定性分析。该项目将检查等离子体不稳定性的特征和后果，并将结果与美国宇航局THEMIS任务的观测结果进行比较。亚暴生长阶段等离子体层的线性和早期非线性不稳定性是理解亚暴扩展起始阶段的关键。稳定性分析的准确性依赖于等离子体薄片结构模型的详细知识。THEMIS亚暴观测将提供更多的输入条件和约束条件，使OpenGGCM模拟能够在亚暴生长阶段重建一系列准确和真实的等离子体层结构。稳定性分析将有助于解决亚暴发生过程中存在的许多争议，并为亚暴发生问题提供新的视角。该项目将有助于提供THEMIS亚暴事件的定量解释，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.