Effects of anisotropic turbulent transport on generation mechanism of the Earth's magnetic field

各向异性湍流输运对地球磁场产生机制的影响

• 批准号: 11640412
• 负责人: MATSUSHIMA Masaki
• 金额: $ 0.7万
• 依托单位: Tokyo Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640412/
• 关键词: Earth's magnetic field; Anisotropic turbulence; Turbulent transport; 地球磁場生成機構; 乱流輪送

It is likely that large-scale fields are transported by small-scale motions in the Earth's fluid core, since molecular diffusivities are very small. Turbulence in the core is anisotropic because of the Earth's rotation, the gravity and the magnetic field. However, the effect of anisotropic turbulence on generation mechanism of the Earth's magnetic field is still unknown. In this research, direct numerical simulations for MHD turbulence are performed to examine the anisotropic turbulent transport. Then the turbulent transport is parameterized in terms of a second moment closure model. It turns out that such a model of turbulent transport expresses that obtained through direct numerical simulations. When an anisotropic eddy diffusivity is artificially employed in numerical simulations, it is found that the magnetic energy increases intermittently even if the kinetic energy is small. This suggests that anisotropic turbulent transport influences large-scale magnetic field generation. The turbulent heat transport is given by a product of an eddy diffusivity tensor and a temperature gradient vector. When an angle between directions of large-scale temperature gradient and gravity is larger than π/2, it is difficult to use a simple model for local turbulence in global numerical simulations.

由于分子差异很小，因此很可能通过地球流体核心中的小规模运动来运输大型田地。核心中的湍流是各向异性的，因为地球的旋转，重力和磁场。但是，各向异性湍流对地球磁场发电机理的影响仍然未知。在这项研究中，进行了直接的MHD湍流数值模拟，以检查各向异性湍流转运。然后，湍流传输是根据第二矩闭合模型进行参数化的。事实证明，这种湍流传输模型表达了通过直接数值模拟获得的。当在数值模拟中人为地进行各向异性涡流难度时，即使动能很小，磁能也会间断地增加。这表明各向异性湍流转运会影响大规模磁场的产生。湍流传输由涡流量张量和温度梯度向量的产物给出。当大尺度温度梯度和重力的方向之间的角度大于π/2时，很难在全局数值模拟中使用简单的模型来用于局部湍流。

项目成果

Matsushima, M.: "Expression of turbulent heat flux in the Earth's core in terms of a second moment closure model"Physics of the Earth and Planetary Interiors. 128. 137-148 (2001)

Matsushima, M.：“用二阶矩闭合模型表达地核中的湍流热通量”《地球和行星内部物理学》。

Matsushima, M.: "Expression, of turbulent flux in the Earth's core"Eos Trans. AGU, 82, Fall Meet. Suppl., Abstract GP31A-0175. F329. (2001)

Matsushima, M.：“地核湍流的表达”Eos Trans。

Matsushima, M.: "Expression of turbulent flux in the Earth's core"American Geophysical Union 2001 Fall Meeting. F329 (2001)

Matsushima, M.：“地球核心湍流的表达”美国地球物理联盟 2001 年秋季会议。

M.Matsushima: "Effects of Anisotropic Turbulent Transport on Genenration Mechanism of the Earth's Magnetic Field"A.G.U.2000 Fall Meeting. F354 (2000)

M.Matsushima：“各向异性湍流传输对地球磁场生成机制的影响”A.G.U.2000 秋季会议。

Matsushima, M.: "Effects of anisotropic turbulent transport on generation mechanism of the Earth's magnetic field"American Geophysical Union 2000 Fall Meeting. F354 (2000)

Matsushima, M.：“各向异性湍流传输对地球磁场产生机制的影响”美国地球物理联盟 2000 年秋季会议。