Modeling of the Magnetohydrodynamic Instability

磁流体动力学不稳定性的建模

• 批准号: 03640390
• 负责人: MIURA Akira
• 金额: $ 1.22万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1991
• 资助国家: 日本
• 起止时间: 1991 至 1993
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-03640390/
• 关键词: MHD Instability; Kelvin-Helmholtz Instability; Magnetopause; Ionosphere; Simulation; Linear Analysis; Boundary Layr; Magnetosheath Magnetic Field; 運動量輸送; 電離層結合効果; 接線応力; ケルビンヘルムホルツ不安定; MHDシミュレ-ション; 超音速流; マグネトポ-ズ; 衝撃波; 降着円盤; 粘性

1. Dependence of the K-H instability on the flow speed and the magnetic field of the magnetosheath was investigated by the 2D MHD simulation. The supersonic shear flow was found to be unstable to the K-H instability. This result suggests that the tail flank boundary of the magnetosphere is also unstable to the K-H instability. By assuming that the unperturbed magnetic field rotates continuously from the magnetosheath direction to the northward direction in the magnetosphere across the magnetopause, it was found that the northward magnetosheath magnetic field is more favorable to the instability than the southward magnetosheath magnetic field. This is because when the magnetosheath magnetic field is southward there appears a magnetic field component parallel to the flow in the rotation of the magnetic field across the magnetopause, which contributes to stabilization of the K-H instability. The velocity boundary layr generated by the K-H instability was found to be thicker when the magnetosheath magnetic field is northward. This result obtained by the simulation is consistent with observations showing that the low latitude boundary layr is thicker when the magnetosheath magnetic field is northward.2. The 3D MHD linear analysis of the K-H instability in the magnetosphere shows that the K-H instability is stabilized by the 3D coupling to the ionosphere (line-tying effect) and the growth rate of the instability decreases with increasing ionospheric Pedersen conductivity. The K-H instability was also found to be stabilized by the unperturbed perpendicular magnetic field in the magnetosphere, which is generated by the ionospheric Pedersen current and is parallel to the flow. When the ionospheric Pedersen conductivity exceeds a critical value, the K-H instability was found to be completely suppressed by the magnetic tension force associated with the unperturbed perpendicular magnetic field in the magnetosphere.

1.利用二维MHD数值模拟研究了K-H不稳定性与磁鞘流速和磁场的关系。超声速剪切流的不稳定性表现为K-H不稳定性。这一结果表明，磁层的尾翼边界也是K-H不稳定性的不稳定区。通过假设未扰动磁场在磁层中穿过磁层顶从磁鞘方向向北连续旋转，发现北向磁鞘磁场比南向磁鞘磁场更有利于不稳定性。这是因为当磁鞘磁场向南时，在磁场穿过磁层顶的旋转过程中出现了平行于气流的磁场分量，这有助于K-H不稳定性的稳定。当磁鞘磁场向北时，由K-H不稳定性产生的速度边界层较厚。模拟结果与观测结果一致，即磁鞘磁场越北，低纬边界层越厚.对磁层K-H不稳定性的三维MHD线性分析表明，磁层K-H不稳定性是通过与电离层的三维耦合（线束缚效应）而稳定的，并且随着电离层Pedersen电导率的增加，不稳定性的增长率减小。K-H不稳定性也被发现是稳定的磁层中的未扰动的垂直磁场，这是由电离层彼得森电流产生的，是平行于流动。当电离层Pedersen电导率超过一个临界值时，K-H不稳定性被磁层中未扰动垂直磁场产生的磁张力完全抑制。

项目成果

Akira MIURA: "Kelvin-Helmholtz Instability at the Magnetospheric Boundary : Dependence on the Magnetosheath Sonic Mach Number" Journal of Geophysical Research. 97. 10655-10675 (1992)

Akira MIURA：“磁层边界的开尔文-亥姆霍兹不稳定性：对磁鞘声波马赫数的依赖”地球物理研究杂志。

Akira MIURA: "Kelvin-Helmholtz Instability at the Magneto-spheric Boundary:Dependence on the Magneto-sheath Sonic Mach Number" Journal of Geophysical Research. 97. 10655-10675 (1992)

Akira MIURA：“磁球边界处的开尔文-亥姆霍兹不稳定性：对磁鞘声波马赫数的依赖性”地球物理研究杂志。

A.Miura: "KelvinーHelmholtz Instability at the Magnetospheric Boundary:Dependence on the Magnetosheath Sonic Mach Number" Journal of Geophysical Research. 97. (1992)

A.Miura：“磁层边界的开尔文-亥姆霍兹不稳定性：对磁鞘声波马赫数的依赖性”地球物理研究杂志 97。（1992）