M. Matsushima $^{a}$
$^{a}$ Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan.
The Earth's outer core is likely to be in a turbulent state because of very small molecular diffusivities of core fluid. Such small-scale motions are influenced by the Earth's rotation and the magnetic field. Then turbulent motions in the core are highly anisotropic. We have been performing direct numerical simulations (DNS) to examine the effect of anisotropic turbulence in the core on geodynamo processes. A very small region in the core is represented in terms of a rectangular box with periodic boundaries, a large-scale buoyancy field is imposed to drive fluid motions, and a uniform magnetic field is imposed. We have so far found that the turbulent transport has a preferred orientation determined by the directions of the rotation axis, the large-scale magnetic field, and the gravity. It is significant to examine the effect of anisotropic eddy diffusivity on larger-scale fields. We here assume a highly anisotropic thermal diffusivity, which is rather artificial, and perform DNS of thermally-driven magneto-turbulence in a rotating system. It turns out that, depending on sets of parameters employed in DNS, turbulent heat transport becomes very efficient intermittently. The magnetic field is also efficiently generated at that time, although kinetic energy is not very large. This arises from locally enhanced small-scale motions. Such processes are characterized by the existence of sharp structures localized in both space and time. When we consider turbulence in the core, its time scale is very short, and therefore these effects on large-scale fields may be averaged out. However, intermittency as mentioned above may be related to dynamics within the so-called tangent cylinder, where intermittent convective motions occur. We examine the relationship between intermittency appeared in MHD turbulence and sets of parameters.