Flip-Flop Transitions of the Magnetic Intensity and Polarity Reversals in the Magnetohydrodynamic Dynamo

Paleomagnetic data reveal that there have been a lot of geomagnetic field intensity transitions after stable polarity states of the time scales of 0.5 to 1 Myr. The transition time scale is of the order of 1000 years. When the dipole reversals take place, the intensity transition is always observed. On the contrary, there are many intensity transitions observed without dipole reversal. We have performed an extensive computer simulation of an MHD dynamo in a rotating spherical shell. The simulated magnetic field exhibits that generated magnetic energy experience a flip-flop type of transitions in its intensity. One transition is accompanied by the polarity reversal of the dipole component of the generated field, while the other two transitions are accompanied by the reversal of the octupole component.