The stability of nongeostrophic perturbations in a baroclinic zonal flow

The stability of a baroclinic zonal flow is studied by means of the method of small perturbations without imposing geostrophic balance on the perturbations. In other respects the present treatment of the stability problem is within the same framework as most other studies on the subject.

The removal of the geostrophic aasumption makes the results applicable to low latitudes and provides thereby some insight into the conditions under which tropical disturbances may form. The theory leads to increased understanding of conditions favoring deviations from geostrophic flow and explains why observed perturbations are for the most part quaaigeostrophic. Furthermore, it reconciles results of some previous studies which within the narrower framework of geostrophic theory appeared unconnected.

Two cases of generalization of previous results by other investigators are studied. The first of these extend results of EADY (1949) and FJÖRTOFT (1950), the second cam extends results obtained by CHARNEY (1947), HOLMBOE (1959), and ÁRNASON (1961). Based on these two cases general stability criteria are proposed.