Three-dimensional MHD dynamo simulation

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Aiming at solving a dynamo problem as a mechanism of the origin of Earth and planetary magnetism, we have performed three-dimensional MHD dynamo simulation. So far, we have found that boundary layers develop depending on the Ekman number and in the layer small-scale phenomena are dominant, when a non-slip boundary condition is given to the velocity field. Therefore, we must evaluate the effect of boundary layers if we want to obtain reliable results of MHD dynamo simulation. In 1998 and 1999, we developed a new computer code for dynamo simulation and compared its results with those derived from our previous code and showed that our new code is valid. Then we modified this code so as to cope with parallel computing. In 2000, we have participated the dynamo benchmark test as an international group attempt. As a result, our results were found to agree with the others and therefore our computer code is as effective as the other codes developed by oversea researchers. From our results, we could find that crude spatial resolution in the radial direction greatly affects the drift rate of the velocity filed pattern. In other words, it is the most important to assure enough resolution in the boundary layers when we examine the results of numerical computation. A hypothetical cylinder, which is tangent to the inner core at its equator and parallel to the rotation axis, is called a tangent cylinder, which is also a boundary layer. The effect of this layer becomes prominent for the non-slip boundary condition. Inside the tangent cylinder, the flow is not violent when the Rayleigh number is small, but for a high Rayleigh number, convective motion becomes active, Such a feature has a great influence on the mechanism of magnetic field creation and variation. As a future work, we should try to under stand the dependence of the Rayleigh number on dynamics inside the tangent cylinder