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.

由于分子的扩散系数非常小，大尺度磁场很可能是通过地球流体核心的小尺度运动来传输的。由于地球自转、重力和磁场的作用，地核的湍流是各向异性的。然而，各向异性湍流对地球磁场产生机制的影响尚不清楚。在本研究中，对MHD湍流进行了直接数值模拟，以检验各向异性湍流输运。然后用二阶矩闭合模型对湍流输运进行参数化。这种紊流输运模型表达了直接数值模拟得到的紊流输运模型。在数值模拟中，人为地引入各向异性涡旋扩散系数，发现即使动能很小，磁能也会间歇性地增加。这表明各向异性湍流输运影响大尺度磁场的产生。湍流热输运由涡流扩散张量和温度梯度矢量的乘积给出。当大尺度温度梯度方向与重力方向之间的夹角大于π/2时，很难在全局数值模拟中使用简单的局部湍流模型。

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 magnetic field generation in the core"The 7th Symposium of Study of the Earth's Deep Interior. 139 (2000)

Matsushima, M.：“各向异性湍流传输对地核磁场产生的影响”第七届地球深层内部研究研讨会。