抄録
Fluid motions in the Earth's core are reviewed. The core consists of a solid inner core and a liquid outer part. The core is supposed to be composed of iron alloys with lighter elements as oxygen and sulfur, which implies that the core is electrically conducting.
Similar to the fluid dynamics on the Earth's surface, Coriolis force plays a predominant role in the core. A remarkable difference lies in that the electromagnetic force, Lorentz force, is considered as equally powerful. Azimuthal flow is expected to be most predominant, which generates a strong toroidal field that is also azimuthal. The helical motions, convective motions modified by the effect of the Earth's rotation, interact with the toroidal field and induce the dipole field. The geomagnetic dipole field is considered to be maintained in this way.
The convection is widely believed to be of compositional convection, which is caused by difference in buoyancy force acting on iron alloys of different composition. However, the convection is more likely of thermal type, which is driven by cooling the top surface of the core by the mantle convection.
