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Contour plot of potential temperature for a simulation of stratified flow over a mountain. The flow in the lee of the mountain is accelerated. In this regime the flow closely resembles a hydraulic jump that may be generated by a flow of constant density with a free surface over an isolated obstacle (e.g. Long, 1953). A geophysical exaples of such a flow include severe downslope windstorms in the lee of major mountain ranges such as the foehn of Switzerland, the bora of Yugoslavia, and the chinook of North America. Numerical studies (see e.g. Scinocca and Peltier,1989; Afanasyev and Peltier, 1996) show that a typical feature of the flow is the emergence of Kelvin-Helmholtz instability in a shear layer that develops between the low-level high velocity jet and the overlying almost stagnant region created by breaking of internal waves over the mountain. Typical K-H rolls are seen in the picture. |
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Evolution of the horizontal wind at the surface. |
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