On the Interactions between the Long Baroclinic Waves and the Mean Zonal Flow

The development of wave motions in a jet-like westerly current is examined on the basis of approximate solutions for the wave motions in a two-level, quasi-geostrophic model. Solutions of the characteristic-value equations show that two different types of amplifying waves may exist. Both types of amplifying wave motions are connected with a transformation of potential energy to kinetic energy. One of the types is found to be connected with a significant transfer of perturbation kinetic energy to mean zonal kinetic energy. Changes of the mean zonal flow caused by the eddy meridional transport of sensible heat and momentum are computed, and demonstrate the existence and the effects of the forced mean meridional circulations. Considerations of the modifications of the generation of perturbation energy connected with the modifications of the mean zonal flow indicate that the actual motion will have the character of a fluctuating state.