Nonlinear generation of large-scale magnetic fields in forced spherical shell dynamos
- Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT (United Kingdom)
In an earlier paper [P. W. Livermore, D. W. Hughes, and S. M. Tobias, ''The role of helicity and stretching in forced kinematic dynamos in a spherical shell'', Phys. Fluids 19, 057101 (2007)], we considered the kinematic dynamo action resulting from a forced helical flow in a spherical shell. Although mean field electrodynamics suggests that the resulting magnetic field should have a significant mean (axisymmetric) component, we found no evidence for this; the dynamo action was distinctly small scale. Here we extend our investigation into the nonlinear regime in which the magnetic field reacts back on the velocity via the Lorentz force. Our main result is somewhat surprising, namely, that nonlinear effects lead to a considerable change in the structure of the magnetic field, its final state having a significant mean component. By investigating the dominant flow-field interactions, we isolate the dynamo mechanism and show schematically how the generation process differs between the kinematic and nonlinear regimes. In addition, we are able to calculate some components of the transport coefficient {alpha} and thus discuss our results within the context of mean field electrodynamics.
- OSTI ID:
- 22038485
- Journal Information:
- Physics of Fluids (1994), Vol. 22, Issue 3; Other Information: (c) 2010 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-6631
- Country of Publication:
- United States
- Language:
- English
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