arXiv Analytics

Sign in


Dynamic nonlinearity in large scale dynamos with shear

Eric G. Blackman, Axel Brandenburg

Published 2002-04-29, updated 2002-07-02Version 2

We supplement the mean field dynamo growth equation with the total magnetic helicity evolution equation. This provides an explicitly time dependent model for alpha quenching in dynamo theory. For dynamos without shear, this approach accounts for the observed large scale field growth and saturation in numerical simulations. After a significant kinematic phase, the dynamo is resistively quenched, i.e. the saturation time depends on the microscopic resistivity. This is independent of whether or not the turbulent diffusivity is resistively quenched. We find that the approach is also successful for dynamos that include shear and exhibit migratory waves (cycles). In this case however, whether or not the cycle period remains of the order of the dynamical time scale at large magnetic Reynolds numbers does depend how on how the turbulent magnetic diffusivity quenches. Since this is unconstrained by magnetic helicity conservation, the diffusivity is presently an input parameter. Comparison to current numerical experiments suggests a turbulent diffusivity that depends only weakly on the magnetic Reynolds number, but higher resolution simulations are needed.

Comments: 21 pages, 5 figures (revised version)
Journal: Astrophys.J. 579 (2002) 359-373
Categories: astro-ph
Related articles: Most relevant | Search more
arXiv:astro-ph/0012053 (Published 2000-12-03)
Synthesis of Small and Large scale Dynamos
arXiv:astro-ph/0012472 (Published 2000-12-22, updated 2001-01-29)
Large scale dynamos with helicity loss through boundaries
arXiv:astro-ph/0207394 (Published 2002-07-18)
The helicity issue in large scale dynamos