Numerical Analysis Seminars: Large-scale magnetic field generation in rotating compressible convection
8 November 2013 14:00 in CM 105
Motivated by observations of astrophysical magnetic fields we consider the (so called) dynamo problem in which a seed magnetic field can be amplified by the motions of an electrically-conducting fluid. Standard mean-field dynamo theory suggests that turbulent convection in a rotating layer of electrically-conducting fluid should be capable of driving a dynamo with a significant large-scale component. By carrying out three-dimensional magnetohydrodynamical simulations, we investigate the specific problem of dynamo action in rotating compressible convection, focusing primarily upon the dependence of the dynamo on the rotation rate. Our simulations indicate that these turbulent compressible flows can drive a dynamo but, even when the layer is rotating very rapidly, we find no evidence for the generation of a significant large-scale magnetic field. We argue that this is because the system produces a negligible alpha-effect, which is one of the key ingredients in any successful mean-field dynamo model. The possible implications of this result for astrophysical dynamos will also be discussed.
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