In order to gain insights into the interaction of buoyancy driven flows and the magnetic fields generated by them, the problem of convection driven dynamos in rotating spherical fluid shells is studied through numerical simulations as a function of a minimum of the physically most relevant parameters. The constraints imposed by rotation on non-magnetic convection are crucial in determining the character and the effects of the magnetic field. High Prandtl number fluids tend to favor strong axisymmetric dipolar fields such as the geomagnetic field, while fluctuating fields dominate in low Prandtl number dynamos. Various forms of time dependence are found as function of the parameters of the problem. While quadrupolar and hemispherical dynamos usually exhibit a oscillatory time dependence, steady large scale components are seen in dipolar cases. Of special interest are "invisible" oscillatory dipolar dynamos in which only part of the toroidal field oscillates. Torsional oscillations and other forms of time dependence will also be discussed. Most of the results have been obtained in collaboration with Dr. R. Simitev.
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