Magnetic field structure in differentially rotating discs
Abstract
In order to gain a better understanding of the processes that may give rise to non-axisymmetric magnetic fields in galaxies, we have calculated field decay rates for models with a realistic galactic rotation curve and including the effects of a locally enhanced turbulent magnetic diffusivity within the disc. In all cases we have studied, the differential rotation increases the decay rate of non-axisymmetric modes, whereas axisymmetric ones are unaffected. A stronger magnetic diffusivity inside the disc does not lead to a significant preference for non-axisymmetric modes. Although Elsasser's antidynamo theorem has not yet been proved for the present case of a non-spherical distribution of the magnetic diffusivity, we do not find any evidence for the theorem not to be valid in general.
- Publication:
-
Geophysical and Astrophysical Fluid Dynamics
- Pub Date:
- 1990
- DOI:
- 10.1080/03091929008219877
- Bibcode:
- 1990GApFD..50..121D
- Keywords:
-
- Galactic magnetic fields;
- hydromagnetics;
- disc dynamos;
- Elsasser theorem