Rare-reversal chaos in two-disk dynamo models.

A systematic comparative study of two-disk dynamo models without friction (the Rikitake model) and with friction has been carried out. It is shown that the sets of chaotic and periodic modes realized in both models are qualitatively similar. We introduce a simple measure of the complexity of a solution, which allows finding the chaotic mode characterized by long-lived quasistationary states with very weak oscillations of variables, ending with a sharp burst of oscillations with a possible transition to the attraction area of the other stationary solution. This transition corresponds to the change in the magnetic field sign. Such a behavior of the field is somewhat similar to the dynamics of the Earth's large-scale field in terms of the chaotic change of zones from one polarity to another. This rare reversal chaos was found in both two-disk dynamo models (without friction and with friction), but in the viscous case, it appears only at weak friction.