In 1971, while a postgraduate student at the University of East Anglia, I discovered a new type of instability which can affect the motion of a rotating, electrically-conducting fluid. This instability arises if the magnetic field increases sufficiently rapidly with distance from the rotation axis, and can occur even if the actual strength of the magnetic field is quite small. Non-axisymmetric waves then grow in amplitude, and propagate slowly, relative to the rotating fluid itself, around the rotation axis.
The applications of such work lie within the liquid core of the Earth, where the Earth's magnetic field originates. Such `field-gradient' instabilities, as they have come to be called, may, for instance, limit the growth of the magnetic field by the so-called `dynamo' process.
J. Fluid Mech. Vol 52, pp 529-541, 1972
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