Interannual Variability of the Southern Hemisphere 500 mb Flow: Regional Characteristics

Studies of the interannual variability of the 500 mb flow in the Southern Hemisphere for 1972–78 have revealed 1) a quasi-biennial fluctuation in the zonal mean geopotential height and westerly wind fields where there is a systematic poleward progression of anomalies, and 2) a longer period fluctuation, primarily in Wave 1, which has been identified with the Southern Oscillation. These phenomena are further studied regionally by considering four 90° sectors. Results show the dominant contributions to the fluctuations in the zonal mean fields come from the Australasian and South Pacific sectors. Only in the Australasian region is the quasi-biennial poleward progression of anomalies strongly evident. The South Pacific is dominated by lower frequency fluctuations associated with the Southern Oscillation. However, the sequences in all four sectors are correlated with those in the zonal mean fields. When the flow is stronger than normal in mid-latitudes it tends to be weaker than normal in low and high latitudes, and vice versa, in all sectors and in the zonal mean.