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

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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.