The Quasi-Biennial Oscillation (QBO): Some Points About the Terrestrial QBO and the Possibility of Related Phenomena in the Solar Interior.

Centre for Atmospheric Science
Department of Applied Mathematics and Theoretcial Physics
Cambridge University
Proc. NATO Adv. Res. Workshop ARW 920946, Paris, October 1993, "The Solar Engine and its Influence on the Terrestrial Atmosphere and Climate", ed. E. Nesme-Ribes, Springer-Verlag 1994 (Vol. 25 of NATO ASI Subseries I, Global Environmental Change, 3-540-58417-X, I/25)

Here are reprints in pdf format (168 kb) and ps.gz format (76 kb).

NB: Thinking about the solar interior has come a long way since this paper was published! Recent developments are noted here. However, the arguments summarized on pages 305-309 of the above (pdf pages 13-17) are still central to understanding the solar interior and the solar tachocline. They show why stratified turbulence tends to drive the Sun's interior away from, not toward, shellular solid rotation -- in turn requiring an interior magnetic field to explain the observed solid rotation.

The argument depends on the `invertibility principle' for potential vorticity along with the implied Rossby-wave propagation mechanism, all of which is standard knowledge in the terrestrial atmosphere-ocean dynamics community. For fundamental reasons, including angular-momentum conservation, there is no such thing as turbulence without waves in this kind of fluid system.

There are many other examples of the tendency of fluctuations to drive a large-scale fluid system away from solid rotation -- `anti-friction', as it might be called. It is commonplace in stratified, rotating fluid systems over a wide range of circumstances. One of the most striking examples is the planet Jupiter, and another is the terrestrial QBO itself, along with its beautiful laboratory analogue, the celebrated Plumb-McEwan experiment. Antifrictional phenomena are commonplace because of the ubiquity of the various wave propagation mechanisms, of which the Rossby-wave mechanism is only one example, and because of the long-range nature of wave-induced angular momentum transport. We may view all these phenomena as illustrating one of the grand themes of physics, the `dynamical organization of fluctuations'.

In the Plumb-McEwan experiment, one takes an annulus of stably stratified fluid and drives it away from solid rotation by doing nothing but jiggle one of the boundaries. The consequent fluctuations in the fluid are organized by the gravity-wave mechanism, bringing about eddy correlations that conspire to transport angular momentum in a particular way.

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