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. 通过二维 MHD 模拟研究了 K-H 不稳定性对流速和磁鞘磁场的依赖性。超音速剪切流被发现对 K-H 不稳定性不稳定。这一结果表明磁层尾翼边界对于 K-H 不稳定性也是不稳定的。通过假设未受扰动的磁场在跨越磁层顶的磁层中从磁鞘方向连续向北方向旋转，发现北向磁鞘磁场比南向磁鞘磁场更有利于失稳。这是因为当磁鞘磁场向南时，会出现一个与穿过磁层顶的磁场旋转流动平行的磁场分量，这有助于稳定K-H不稳定性。当磁鞘磁场向北时，K-H不稳定性产生的速度边界层更厚。模拟结果与观测结果一致，即磁鞘磁场北向时低纬度边界层较厚。 2．磁层 K-H 不稳定性的 3D MHD 线性分析表明，K-H 不稳定性通过与电离层的 3D 耦合（线系效应）而稳定，并且不稳定性的增长率随着电离层 Pedersen 电导率的增加而降低。还发现磁层中未受扰动的垂直磁场可以稳定 K-H 不稳定性，该磁场由电离层 Pedersen 电流产生且与流动平行。当电离层 Pedersen 电导率超过临界值时，发现 K-H 不稳定性被与磁层中未受扰动的垂直磁场相关的磁张力完全抑制。

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）