Effects of anisotropic turbulent transport on generation mechanism of the Earth's magnetic field

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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.