The Onset of Blocking and Cyclogenesis in Southern Hemisphere Synoptic Flows: Linear Theory

Abstract

A study is made of the instability properties of two instantaneous Southern Hemisphere synoptic flow fields. The growth rates, phase frequencies, perturbation streamfunctions and, for some modes, eddy heat and momentum fluxes of growing disturbances are obtained using a linear, spherical, five-level, quasi-geostrophic model. Both the zonally averaged and three-dimensional flow fields are studied and the eigenmodes are compared with the observed regions of the onset of blocking and of developing midlatitude cyclones. The two principal latitude bands of development are picked out by the instability solutions for the zonally averaged basic flows. For the three-dimensional basic states, the linear solutions reproduce the geographical locations of some of the principal regions of the onset of blocking and cyclogenesis reasonably well.