Stability properties of mean flows with turning

The linear properties of eddies evolving in a mean flow that has backing or veering with height are analyzed. Several rates of turning are considered; the results for a 45˚ difference between the surface and upper level wind directions are illustrative and discussed in detail. The net compass orientation of the wind speed is also varied yielding results cognate with a previous article. Though the root mean square wind speed is unchanged, turning can significantly increase the growth rates since the sum of the two components of the vertical shear may be increased. The fastest growing wave has its wavefront aligned approximately perpendicular to the direction of the upper level flow. The wave properties are most easily influenced by the mean flow that is orthogonal to its wavefront. Thus waves moving parallel to the slow low-level flow propagate slower and are more bottom trapped than the waves moving with the faster upper flow. When there is turning, the relative importance of the variable Coriolis parameter is diminished.