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Convection Driven Dynamos in Rotating Spherical Shells

Thursday, March 21, 2002 - 1:30pm - 2:30pm
Keller 3-180
F. H. Busse (University of Bayreuth)
Numerical simulations of the generation of magnetic fields by convection flows in rotating spherical shells have been carried out in collaboration with R. Simitev for the parameter space spanned by the Rayleigh number, Taylor number, Prandtl number, and magnetic Prandtl number. A wide variety of dynamos have been found and their areas of predominance have been mapped in the parameter space. Since the structure of the magnetic field often reflects the character of the convection flow considerable efforts have been expanded to understand the properties of turbulent convection in the absence of a magnetic field. The numerical simulations exhibit coherent structures such as localized convection and relaxation oscillations. Of particular interest are regimes in the parameter space where the magnetostrophic approximation is approximately valid and scaling relationships can be obtained. The difficulty of reaching low magnetic Prandtl numbers casts some doubts on the extrapolation of presently available dynamo models to the case of the Earth�s core.