▪ Abstract  New developments have occurred in recent years in the field of dynamo theory. The increase in computer capacity has permitted simulations of convection-driven dynamos in rotating spherical fluid shells in parameter ranges much closer to those of the Earth's core than has been possible before. The progress in handling flows of liquid sodium in large containers, on the other hand, has opened opportunities for realizations of homogeneous dynamos in the laboratory. These developments will lead to a deeper understanding of the origin of magnetic fields in planets and in stars.

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At Taylor numbers of the order 10(8) and Prandtl numbers of the order 1, dynamos generated by convection are found for which the magnetic field is essentially confined to either the northern or the southern hemisphere of a rotating spherical shell. The time dependence is typically chaotic, but latitudinal waves can be discerned that cause the magnetic field to change its polarity in a cyclical fashion. A possible relationship to a solar phenomenon is pointed out.

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