Abstract:

The large-scale magnetic Ðelds of stellar and galactic bodies are generally understood to be organized and ampliÐed by motions in the conducting Ñuid media of these bodies. This article examines a mechanism by which continual excitation of the conducting Ñuid by small-scale Ðelds results in production of large-scale Ðelds. The excitation of the induction equation by small-scale Ðelds is parameterized as stochastic forcing, and the crucial role of the nonnormality of the induction operator in determining the spatial and temporal structure of variation in the large-scale Ðelds is emphasized. A cylindrically symmetric helical Ñow is used to provide illustrative examples.