Abstract
By making use of a two-level, quasi-geostrophic model without friction or heat sources, the rates of change of disturbances with time are discussed. In case of using the technique of the linearized perturbation theory, where the disturbances are considered to be small perturbations superimposed on a zonal basic current, the amplitudes of disturbances are not uniquely determined, while the rates of amplification of amplitudes with time are obtained as the exponential type in relation with the wave length of disturbance and the vertical shear of the basic current.
In this paper, the second-order effects on the zonal current and also on the mean static stability of the domain we concerned with due to the presence of very simple unstable baroclinic waves are considered. In this discussion, it is qualitatively shown that the small amplitude perturbation grows at first and later the zonal current is modified by the action of the northward eddy transport of sensible heat, while the vertical eddy transport of entropy changes the mean static stability. Both effects controll the exponential amplification of amplitude of unstable disturbance with time. Basing upon the qualitative considerations which are obtained theoretically from the simple model, we perform the numerical experiment where the time changes of disturbances are presented quantitatively.
