Magnetic field reversal and magnetic circuit in a thermally driven MHD dynamo

Mechanism of magnetic field generation in a celestial body is investigated numerically. As a minimal model we study the dynamics of a Boussinesq MHD fluid confined between two rotating concentric spheres of uniform temperature. Five pairs of thermally driven convection columns are formed, which are robust against magnetic field generation. The activity of the magnetic field changes randomly in time. The global structure of the magnetic field outside the outer sphere is reversed rather periodically. It is also observed that closed bundles of strong magnetic field lines connecting two nearest anticyclonic convection columns are generated synchronously with the magnetic field reversal. (author)