| Abstract: | The structure of the critical layer in a stratified shear flow is investigated for finite-amplitude waves at high Reynolds numbers. Under such conditions, which are characteristic of the Clear Air Turbulence environment, nonlinear effects will dominate over diffusive effects. Nevertheless, it is shown that viscosity and heat-conduction still play a significant role in the evolution of such waves. The reason is that buoyancy leads to the formation of thin diffusive shear layers within the critical layer. The local Richardson number is greatly reduced in these layers and they are, therefore, likely to break down into turbulence. A nonlinear mechanism is thus revealed for producing localized instabilities in flows that are stable on a linear basis. The analysis is developed for arbitrary values of the mean flow Richardson number and results are obtained numerically. |
