Abstract
Unsteady fast dynamos are constructed using a sequence of rapid movements separated by periods of diffusion of the magnetic field. Motivated by the physical mechanism described by Zel'dovich and by Soward, we examine the effect of single-mode Beltrami waves applied sequentially, and show that they can be approximated by a simple “stretch-fold-shear” (SFS) map of the unit cube onto itself. In the SFS map, the field points in a fixed direction and diffusion is easily computed. The numerical results indicate that fast dynamo action occurs for sufficiently large shear, and that the process is primarily a coherent feature of the larger magnetic scales. Similar results are obtained for smooth flows. Some preliminary analysis of the SFS map using a decomposition method is described.
Original language | English (US) |
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Pages (from-to) | 211-240 |
Number of pages | 30 |
Journal | Geophysical & Astrophysical Fluid Dynamics |
Volume | 44 |
Issue number | 1-4 |
DOIs | |
State | Published - Dec 1988 |
Keywords
- : Kinetic dynamos
- fast dynamos
ASJC Scopus subject areas
- Computational Mechanics
- Astronomy and Astrophysics
- Geophysics
- Mechanics of Materials
- Geochemistry and Petrology