NOTES AND CORRESPONDENCE Interdecadal Variation of the Southern Hemisphere Circulation

Previous studies examining the seasonal contrast and spatial structure of the interdecadal variation in the Southern Hemisphere (SH) atmospheric circulation and the relationship between this interdecadal variation and cyclone activity have been extended using the SH data generated by the Australian Bureau of Meteorology for 1972–92. The major findings of this study are the following: 1) In addition to the deepening of the circumpolar trough and the increase of midlatitude sea level pressure (SLP) in winter, a zonal wavenumber 3 pattern appears in the high middle latitudes. During summer, the interdecadal change is dominated by three latitudinal zones of SLP anomalies with negative values in low and high latitudes and positive values in midlatitudes. 2) A zonal wavenumber 3 pattern that develops during the winter persists into early spring, while the three latitudinal SLP anomaly zones that emerge in late spring and early summer continue on through the summer. 3) An enhancement of cyclone activity is associated with the deepening of the SH circumpolar low centers.