Abstract
A brief review is given of a series of analytical studies by the authors demonstrating the effects of second order nonlinear and nongeostrophic processes on the evolution of an amplifying two-level baroclinic wave. It is shown that many of the finite amplitude properties of the waves observed in the atmosphere and ocean can be deduced. However, in these studies the feedback between the altered basic state and the lower order (primary) wave field is neglected so that the waves grow in an unrealistic exponential manner without reaching saturation (i.e., occlusion). In order to demonstrate the saturation effects of feedbacks between the static stability and baroclinicity (vertical wind shear) variations and the growing primary wave, a heuristic semi-numerical algorithm is developed that, in principle, can be coupled with the previous analytical studies. It is found that for a typical initial basic state, and in the absence of friction and barotropic wave-wave and wave-mean flow interactions, the time scale for the development of an occluded state is about 10days for the atmosphere and 2 months for the ocean. In both cases the effects of baroclinicity variations are much more important than static stability variations in bringing the wave to saturation. Because friction is neglected the ultimate decay of the occluded wave cannot be represented.
