Interaction between the low- and high-frequency transients in the Southern Hemisphere winter circulation

A symbiotic relationship between the high- and low-frequency transients in the Southern Hemisphere has been examined by using ECMWF analyses of 500 mb geopotential height and temperature fields over 9 winter seasons. The low-frequency transients organize the high-frequency eddies over the regions where low-frequency westerly anomalies prevail, forming traveling storm tracks that move together with the low-frequency waves. The high-frequency eddies, in turn, reinforce the barotropic component of the low-frequency waves while tending to diminish the baroclinic component of the low-frequency waves. All of these findings give further credence to earlier results for the Northern Hemisphere. As a supplementary to the feedback analyses, the energetics analysis for the winter seasons in both the Northern and the Southern Hemispheres reveals that the forcing of the low-frequency flow by the high-frequency transients in the Southern Hemisphere is much stronger than in the Northern Hemisphere. The contribution of the stationary waves to maintenance of the low-frequency flow through barotropic instability is significantly less in the Southern Hemisphere.