AN EARTH-LIKE NUMERICAL DYNAMO MODEL

The mechanism by which the Earth and other planets maintain their magn etic fields against ohmic decay is among the longest standing problems in planetary science. Although it is widely acknowledged that these f ields are maintained by dynamo action, the mechanism by which the dyna mo operates is in large part not understood. Numerical simulations of the dynamo process in the Earth's core(1-4) have produced magnetic fie lds that resemble the Earth's field, but it is unclear whether these m odels accurately represent the extremely low values of viscosity belie ved to be appropriate to the core. Here we describe the results of a n umerical investigation of the dynamo process that adopts an alternativ e approach(5) to this problem in which, through the judicious choice o f boundary conditions, the effects of viscosity are rendered unimporta nt. We thereby obtain a solution that at leading order operates in an Earth-like dynamical regime. The morphology and evolution of the magne tic field and the fluid flow at the tore-mantle boundary are similar t o those of the Earth, and the field within the core is qualitatively s imilar to that proposed on theoretical grounds(6).