Study of Mechanism of MHD dynamo-Toward Understanding of Geodynamo-

作为地球动力学最简单的模型之一，对旋转球壳中热驱动磁场的产生和维持机理进行了数值研究。在项目期间，我们获得了以下有趣的结果。这是世界上第一次在计算机上不经任何简化地求解MHD方程，实现了强磁场的产生和磁偶极子的准周期振荡。通过对闭合流线和滞止点的详细分析，阐明了产生磁场的热对流的完整三维结构。速度空间结构与磁场之间的关系目前正在研究这些流线以及速度梯度张量的本征值分析。发现磁偶极矩的准周期反转，在磁场和速度场中都存在复杂而有规则的时变。通过运动学MHD仿真，揭示了速度与磁场之间存在很强的空间相关性。

The mechanism of generation and sustenance of magnetic field driven thermally in a rotating spherical shell was investigated numerically as one of the simplest models of geody-namo. During the period of the project we obtained the following interesting results. [1] It is the first time in the world that the generation of a strong magnetic field and a quasi-periodic oscillation of magnetic dipole are realized on a computer by solving the MHD equations with-out any simplification. [2] The full three-dimensional structure of the thermal convection which creates the magnetic field was clarified by a detailed analysis of closed streamlines and stagnation points. The relation between the spatial structures of the velocity and the magnetic field is currently being investigated in terms of these streamlines as well as by the eigen-value analysis of the velocity-gradient tensor. [3] It was found that there is a complicated but regular time-variation in both the magnetic and the velocity fields which cause the above-mentioned quasi-periodic reversal of the magnetic dipole moment. [4] A kinematic MHD simulation was performed to reveal that there is a strong spatial correlation between the velocity and the magnetic fields.