Middle atmospheric dynamics and transport: some
current challenges to our understanding.

Michael E. McIntyre

In: Dynamics, Transport and Photochemistry in the Middle Atmosphere of the Southern Hemisphere, Proc. San Francisco NATO Workshop, ed. A. O'Neill; Dordrecht, Kluwer, pp. 1-18 (1990).

This invited conference paper, available here as a pdf scan (2.7Mbyte, © 1990 Kluwer), is centred around `the tendency for naturally-occurring turbulence to be spatially inhomogeneous', a conspicuous tendency that's incompatible with the standard assumptions of classical turbulence theory. Examples include not only ocean-beach breakers and `what can be seen out of aeroplane windows', but also the tendency of large-scale, layerwise-two-dimensional turbulence to self-limit by forming what are now called `eddy-transport barriers' -- back in 1990 I called them `PV barriers' -- of the kind so well illustrated by the sub-polar and subtropical eddy-transport barriers in the wintertime stratosphere.

I now think that `eddy-transport barriers' is the best term, emphasizing first that they are barriers to layerwise-two-dimensional eddy transport but not to mean transport (by diabatic or residual mean circulations), and second that isentropic gradients of potential vorticity (PV) are not the only factor. As Martin Juckes and I pointed out in 1987, the peculiar resilience of these barriers, even down to small scales and even for aperiodic disturbances, is related not only to PV gradients and the consequent Rossby-wave quasi-elasticity but also to shear. For a recent review see my 2008 paper with David Drischel in the Journal of the Atmospheric Sciences, 65, 855-874, Multiple jets as PV staircases: the Phillips effect and the resilience of eddy-transport barriers (.pdf, 1.5 Mbyte, © 2008 American Meteorological Society) and for a key theoretical development beyond that review a NEW paper by Richard Wood and myself, A general theorem on angular-momentum changes due to potential vorticity mixing and on potential-energy changes due to buoyancy mixing, now out in J. Atmos. Sci 67, 1261-1274. Its corollaries include a new nonlinear stability theorem for shear flows.

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Michael Edgeworth McIntyre (mem at damtp.cam.ac.uk), DAMTP, University of Cambridge, Silver Street, Cambridge CB3 9EW

Last updated 30 May 2011
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