MAG (IPGP & ENS), CNRS UMR7154, LRA Département de Physique - 24 rue
Lhomond, 75005 Paris France, EU
Abstract. The geo and solar magnetic fields have long been thought to be very different objects both in terms of spatial structure and temporal behavior. The recently discovered field structure of a fully convective star is more reminiscent of planetary magnetic fields than the Sun's magnetic field (Donati J.-F. et al., Science, 311 (2006) 633), despite the fact that the physical and chemical properties of these objects clearly differ. This observation suggests that a simple controlling parameter could be responsible for these different behaviors. We report here the results of threedimensional simulations which show that varying the aspect ratio of the active dynamo region can yield a sharp transition from Earth-like steady dynamos to Sun-like dynamo waves.