Turbulent convection and magnetic field of the outer Earth's core

The currently available data on physical properties of the outer Earth's co re have been analyzed. Rayleigh number for the outer core may range from 10 (16) to 10(18), and there is a developed turbulent convection in the outer core. It is shown that the temperature drop in the outer core is three orde rs of magnitude lower than it is in the lower mantle for a heat flux equal to the average heat flux at the Earth's surface. A horizontal temperature g radient exists at the core-mantle boundary because of a great temperature d ifference between the ascending and descending flows in the lower mantle. T he horizontal temperature gradient, in turn, gives rise to intense horizont al convective flows. But even with constant temperature of the core-mantle boundary, convection rolls with a now velocity of about of 10(-5) m/s occur at this boundary. In this case, the velocity of a large-scale flow ranges from 0.012 to 0.045 m/s. Based on a theoretical analysis and experimental d ata, the authors have found a maximum horizontal flow velocity and boundary -layer thickness depending on the horizontal temperature gradient. The maxi mum flow velocity and the boundary-layer thickness at the core-mantle bound ary have been calculated for possible temperature gradient variations. We consider an influence of the Coriolis force on the convective-now struct ure at the core-mantle boundary. There are oppositely directed vortex flows in the southern and northern hemispheres near the core-mantle boundary. Th ese vortex flows occur far enough from the equator, i.e., where the Corioli s force manifests itself. Electric charges may arise at a boundary between two media which differ gre atly in electric properties, e.g., at the core-mantle boundary. As the char ged particles are in the vortical motion, a magnetic field arises. The para meters of a single vortex depending on the now velocity have been evaluated , as well as the concentration of charged particles necessary to generate a magnetic field with magnetic induction equal to the terrestrial one. The c urrent density required for generation of such a magnetic field is equal to 0.001-0.01 mu A/mm(2) at a horizontal velocity of 0.1-1 m/s. According to the model considered, the Earth's magnetic field represents the superpositi on of magnetic fields of systems of vortices located at distances far away from the equator in the northern and southern hemispheres at the core-mantl e boundary. The main conclusions resulting from the model under considerati on have been formulated.