Mountain Waves and Clear Air Turbulence

Abstract

It has been observed that h igh level Clear Air Turbulence (CAT)occurs frequently in places such as Japan and Australia, where a fairly strong jet stream crosses a chain of mountains. If a suitable size mountain occurs somewhere in a mountain range, it is shown that the shear stresses generated by lee waves under conditions of a simple (triangular velocity profile) jet stream, and a fairly realistic (ICAO standard) temperature profile are well able to explain the presence of turbulence. The thickness of the strong shear layers is similar to the observed thickness of typical patches of turbulence. However under the conditions mentioned, it is found that strong shear layers occur to very great heights in the atmosphere, whereas much of the data on frequency of occurrence of CAT tends to show lower probabilities of occurrence at higher altitudes.