Abstract
The ‘anti-dynamo’ theorems (ADTs) impose restrictions on the symmetry properties of the velocity and magnetic fields associated with sustained dynamo action in an electrically conducting body of fluid, such as the Earth's core. However, several of these ADTs depend on the assumption that the fluid flow is incompressible, and we show here that their validity is queried when compressible flow is considered. In particular, non-stationary axisymmetric dynamos may no longer be prohibited by Cowling's theorem. The high degree of axisymmetry of Saturn's magnetic dipole, revealed by the recent Pioneer 11 flyby, may be related to the planet's large compressibility.
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Todoeschuck, J., Rochester, M. The effect of compressible flow on anti-dynamo theorems. Nature 284, 250–251 (1980). https://doi.org/10.1038/284250a0
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DOI: https://doi.org/10.1038/284250a0
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