| Project/Area Number |
06640566
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Space and upper atmospheric physics
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| Research Institution | University of Tokyo |
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Principal Investigator |
MIURA Akira University of Tokyo, Graduate School of Sciences, Assistant Researcher, 大学院・理学系研究科, 助手 (20126171)
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| Project Period (FY) |
1994 – 1996
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| Project Status |
Completed (Fiscal Year 1996)
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| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1996: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1995: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1994: ¥800,000 (Direct Cost: ¥800,000)
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| Keywords | Magnetopause / Kelvin-Helmholtz Instability / Enstrophy / Ionosphere / Momentum Transport / Vortex / Plasma / MHD Simulation / 電磁流体不安定 / 沿磁力線電流 / 加速 / 非線型 / 磁気流体 / 不安定 / モデリング / シミュレーション / マグネトポ-ズ / 磁気圏境界 / 磁気圏境界面 / 境界層 / 惑星間空間磁場 |
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| Research Abstract |
1. Owing to the continuous rotation of the zero-th order magnetic field across the magnetopause the Kelvin-Helmholtz (K-H) instability is more easily excited when the magnetosheath magnetic field is northward than when it is southward. The thickness of the velocity boundary layr at the magnetopause becomes larger when the magnetosheath magnetic field is northward owing to the momentum transport by the K-H instability. When the magnetosheath magnetic field is not due north, a slow rarefaction region is formed near the vortex, wherein the plasma is rarefied and accelerated along the field line.
2. The conservation law of the enstrophy is derived for the 2-D compressible plasma (fluid) motion transverse to the magnetic field. An MHD simulation for the 2-D transverse configuration, where the magnetic field is transverse to the flow velocity, shows that owing to the vortex pairing in the nonlinear stage of the K-H instability the transported momentum and the anomalous viscosity become much larger than those due to the linearly fastest growing vortex. Inside the vortex the plasma is rarefied strongly by the fast magnetosonic rarefaction and the magnetic pressure is reduced inside the vortex. The flow velocity is enhanced at the periphery of the vortex, which is formed by the K-H instability.
3. In the 3-D magnetosphere-ionosphere coupling system the K-H instability is suppressed completely when the ionospheric conductivity is higher than a critical conductivity, which is nearly equal to the Alfven conductance averaged along the field line. This is due to a stabilizing influence of the transverse magnetic field in the magnetosphere, which is produced by the transverse electric field causing the sheared velocity flow in the magnetosphere.
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