Interannual (ENSO) and Interdecadal (ENSO-like) Variability in the Southern Hemisphere Tropospheric Circulation*

Recent work has identified variability in the Pacific Ocean SST with a structure qualitatively similar to ENSO, but at lower frequencies than ENSO. Zhang et al. have documented the atmospheric circulation anomalies in the Tropics and Northern Hemisphere that are associated with decadal ENSO-like variability and compared these anomalies to those associated with the (interannual) ENSO cycle. Here the authors extend the study of Zhang et al. to the Southern Hemisphere using the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis data for 1958–96. Consistent with previous studies, the Southern Hemisphere circulation anomalies associated with ENSO display a teleconnection pattern from the central tropical Pacific into the far southeastern Pacific Ocean. Comparatively larger circulation anomalies are found in the Southern Hemisphere associated with the decadal ENSO-like variability, though aloft the structure of the anomalies emphasizes the polar vortex with an adorning wavenumber-3 anomaly along 60°S. There is a common pattern of SST anomalies throughout the South Pacific associated with the ENSO and the decadal ENSO-like variability, and these anomalies appear to be forced by (inferred) surface heat flux anomalies that should be associated with the changes in the atmospheric circulation. Finally, subtle differences in the tropical circulation anomalies are found to be associated with the two different timescales of variability. Further studies are required to demonstrate whether these differences are responsible for the different structure of the tropospheric mid- and high-latitude circulation anomalies in the Northern and Southern Hemispheres.