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Fast dynamo action in unsteady flows and maps in three dimensions

1987; American Physical Society; Volume: 59; Issue: 14 Linguagem: Inglês

10.1103/physrevlett.59.1573

1092-0145

B. J. Bayly, Stephen Childress,

Astro and Planetary Science

Unsteady fast dynamo action is obtained in a family of stretch-fold-shear maps applied to a spatially periodic magnetic field in three dimensions. Exponential growth of a mean field in the limit of vanishing diffusivity is demonstrated by a numerical method which alternates instantaneous deformations with molecular diffusion over a finite time interval. Analysis indicates that the dynamo is a coherent feature of the large scales, essentially independent of the cascade of structure to small scales.