The presence of a magnetic field can make a portion of compressible fluid less dense than its surroundings, so that it floats upward under the influence of gravity. This magnetic buoyancy is thought, in fact, to be the mechanism by which magnetic flux tubes rise through the Sun's convection zone and break at the surface in the form of sunspots.
The rate at which these magnetic flux tubes rise is of major interest, and was once thought to be far too fast, in fact, for the self-consistency of the whole picture. My own contribution was to show that the Sun's rotation would have a major effect on the process, by drastically reducing the rate at which the magnetic buoyancy instabilities develop. I argued, too, that it would substantially lengthen the time taken for the flux tubes to reach the surface.
Nature Vol 277, pp 41-42, 1979
Solar Phys. Vol 62, pp 23-50, 1979
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