Physical Mechanism of Generation and Reversals of Geomagnetic Dynamo

地磁发电机产生和反转的物理机制

• 批准号: 13680566
• 负责人: SATO Tetsuya
• 金额: $ 1.98万
• 依托单位: Japan Agency for Marine-Earth Science and Technology (JAMSTEC) (2002-2003)National Institute for Fusion Science (2001)
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2003
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13680566/
• 关键词: Geodynamo; Geomagnetic field; Yin-Yang grid; MHD dynamo; Simulation; Earth Simulator; 磁場気ダイナモ; 磁気流体ダイナモ; 磁気流体力学; 自己組織化; ダイポール; ダイナモ; 磁場の逆転; 仮想現実; バリアフリー操縦; MHD; 磁場逆転

The Earth's magnetic field has two intriguing features ; one is its dipole nature ; and the other is its reversal of the north-south polarity. The purpose of this study is to simulate these features of the geomagnetic field and to understand the physical mechanism behind it by means of large scale computer simulation. The simulation model is as follows : We consider a spherical shell region between two concentric spheres. The temperatures of the spherical boundaries are kept constant and uniform ; the inner sphere is hot and outer sphere is cold. An electrically conducting fluid is confined in this spherical shell region, corresponding to the liquid iron in the Earth's outer core. When the temperature difference is sufficiently large, convection motion of the electrically conducting fluid sets about. The fundamental equations are the magnetohydrodynamic (MHD) equations with time development equations of temperature field. As a result of our computer simulation, spontaneous generation o … More f dipole magnetic field and its intermittent reversals are successfully reproduced. detail analysis of the simulation data indicates that the dynamo-generated magnetic field has two stable states ; one is high energy state and the other is low energy state. One of interesting findings in this simulation is hat the dipole reversals take place only in the high energy state. Another interesting finding is that quadrupole moment grows, exceeding the dipole moment before the reversal. The computational grid system used in our simulation, by which we could successfully reproduced the dipole field generation and reversals, were spherical latitude-longitude grid. When we applied this code to the Earth Simulator, we found that the latitude-longitude grid is not suitable to this vector-parallel architecture. We, therefore, devised a new kind of spherical grid system based on the overset (or Chimera) grid methodology, and named it Yin-Yang grid. The Yin-Yang grid is successfully applied to the spherical shell MHD dynamo simulation. Less

地球磁场有两个有趣的特征；一是其偶极子性质；另一个是南北极性的逆转。这项研究的目的是通过大规模计算机模拟来模拟地磁场的这些特征并了解其背后的物理机制。仿真模型如下：我们考虑两个同心球之间的球壳区域。球面边界的温度保持恒定且均匀；内球是热的，外球是冷的。导电流体被​​限制在这个球壳区域，对应于地球外核中的液态铁。当温差足够大时，导电流体开始对流运动。基本方程是磁流体动力学（MHD）方程和温度场时间发展方程。我们的计算机模拟结果成功地再现了偶极子磁场的自发产生及其间歇性反转。仿真数据的详细分析表明发电机产生的磁场有两个稳定状态；一种是高能态，另一种是低能态。该模拟中有趣的发现之一是偶极子反转仅发生在高能态。另一个有趣的发现是四极矩增大，超过了反转之前的偶极矩。我们的模拟中使用的计算网格系统是球形经纬度网格，通过它我们可以成功地再现偶极子场的产生和反转。当我们将此代码应用到地球模拟器时，我们发现经纬度网格不适合这种矢量并行架构。因此，我们基于重叠（或Chimera）网格方法设计了一种新型球形网格系统，并将其命名为阴阳网格。阴阳网格成功应用于球壳MHD发电机模拟。较少的

项目成果

J.Li, T.Sato, A.Kageyama: "Repeated and Sudden Reversals of the Dipole Field Generated by a Spherical Dynamo Action"Science. 295 5561. 1887-1890 (2002)

J.Li、T.Sato、A.Kageyama：“球形发电机作用产生的偶极子场的反复和突然反转”科学。

佐藤哲也: "地球シミュレータ -ホリスティック・シミュレーションと科学革命-"日本物理学会誌. Vol.58 No.2. 79-85 (2003)

佐藤哲也：“地球模拟器 - 整体模拟和科学革命”日本物理学会杂志第 58 卷第 79-85 期（2003 年）。

佐藤哲也: "地球ダイナモ〜地磁気の生い立ちと逆転の物語〜"AESTO NEWS. No.1. 2-2 (2002)

佐藤哲也：“地球发电机 - 地磁的历史和逆转的故事”AESTO NEWS 第 1 期（2002 年）。

Masaki Yoshida, Akira Kageyama: "Application of the Yin-Yang grid to a thermal convection of a Boussinesq fluid with infinite Prandtl number in a three-dimensional spherical shell"Geophysical Research Letters. (in press). (2004)

Masaki Yoshida、Akira Kageyama：“阴阳网格在三维球壳中具有无限普朗特数的 Boussinesq 流体的热对流中的应用”地球物理研究快报。

Y.Tamura, A.Kageyama, T.Sato, S.Fujiwara, H.Nakamura: "Virtual reality system to visualize and auralize numerical simulation data, Comput"Computer Physics Communications. 142. 227-230 (2001)

Y.Tamura、A.Kageyama、T.Sato、S.Fujiwara、H.Nakamura：“可视化和可听化数值模拟数据的虚拟现实系统，Comput”计算机物理通信。