Modeling of the Hydromagnetic Instability

磁流体不稳定性建模

• 批准号: 06640566
• 负责人: MIURA Akira
• 金额: $ 1.47万
• 依托单位: University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06640566/
• 关键词: 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

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.

1.由于磁层顶零阶磁场的连续旋转，磁鞘磁场向北时比向南时更容易激发Kelvin-Helmholtz（K-H）不稳定性。当磁鞘磁场偏北时，由于K-H不稳定性的动量输运，磁层顶的速度边界层厚度变大。当磁鞘磁场不是正北时，在涡旋附近形成一个缓慢的稀薄区域，其中等离子体被稀薄并沿着场线加速。导出了二维可压缩等离子体（流体）横向于磁场运动的涡度拟能守恒律。对磁场横向于流速的二维横向位形的MHD模拟表明，在K-H不稳定性的非线性阶段，由于涡旋配对，输运的动量和反常粘滞系数比线性增长最快的涡旋所产生的动量和反常粘滞系数大得多。在涡旋内部，等离子体被快速的磁声稀薄作用强烈地稀薄化，涡旋内部的磁压降低。在K-H不稳定性的作用下，旋涡周围的流速增加.在三维磁层-电离层耦合系统中，当电离层电导率大于某一临界电导率时，K-H不稳定性被完全抑制，该临界电导率几乎等于沿场线沿着平均的Alfven电导。这是由于磁层中的横向磁场的稳定影响，这是由横向电场引起的剪切速度流在磁层中产生的。

项目成果

A.Miura: "Kelvin-Helmholtz instability at the magnetopause:Computer simulations" Physics of the Magnetopause,Geophysical Monograph90. 285-291 (1995)

A.Miura：“磁层顶的开尔文-亥姆霍兹不稳定性：计算机模拟”磁层顶物理学，地球物理专着90。

A.Miura: "Dependence of the magnetopause Kelvin-Helmholtz instability on the orientation of the magnetosheath magnetic field" Geophys.Res.Lett.22. 2993-2996 (1995)

A.Miura：“磁层顶开尔文-亥姆霍兹不稳定性对磁鞘磁场方向的依赖性”Geophys.Res.Lett.22。

Miura,A.: "Physics of the Magnetopause" B.U.O.Sonnerup,P.Song,M.F.Thomsen (in press), (1995)

Miura,A.：“磁层顶物理学”B.U.O.Sonnerup、P.Song、M.F.Thomsen（印刷中），（1995 年）

A.Miura: "Kelvin-Helmholtz instability at the magnetopause : Computer simulations" Physics of the Magnetopause, ed. by P.Song AGU. 285-291 (1995)

A.Miura：“磁层顶的开尔文-亥姆霍兹不稳定性：计算机模拟”磁层顶物理学，编辑。

A.Miura: "Stabilization of the Kelvin-Helmholtz instability by the transverse magnetic field in the magnetosphere-ionosphere coupling system" Geophys.Res.Lett.23,7. 761-764 (1996)

A.Miura：“磁层-电离层耦合系统中横向磁场对开尔文-亥姆霍兹不稳定性的稳定”Geophys.Res.Lett.23,7。