Periodic Reversals of Magnetic Field Generated by Thermal Convection in a Rotating Spherical Shell

The generation and reversals of the magnetic field are investigated by the use of direct numerical simulation of a thermally driven MHD Boussinesq flow in a rotating spherical shell. Moderately strong magnetic field, the energy of which is 30% of the kinetic, is generated in a thermal convection field composed of five pairs of cyclonic and anti-cyclonic vortex columns. The dipole moment of the magnetic field aligns with the rotation axis of the shell most of the time, and changes the direction almost periodically. The magnetic field itself is also reversed simultaneously. The intensity of the dipole moment becomes weak at the transition times.