Evidence of decadal variability in the Pacific region is large-scale changes in the winter circulation pattern over the North Pacific during the mid-1970s, which are coherent with changes in the El Niño-Southern Oscillation (ENSO) events in the Tropics.

One of the main features involved in this decadal climate variability is low-frequency sea surface temperature (SST) variability. Recent studies have suggested two such plausible SST patterns. One is called the ‘decadal ENSO-like SST pattern’. This pattern is very similar to the interannual ENSO SST pattern but with variability longer than 10 years. The other pattern is described as the North Pacific decadal SST variability and is not related to the above decadal ENSO-like pattern.

The aim of this project is to clarify the links between the tropical and mid-latitude Pacific circulation on decadal timescales and its relevance to variability in the Southern Hemisphere using the Mark2 CSIRO Coupled Ocean-Atmosphere General Circulation Model (Mark2 CGCM). Empirical Orthogonal Function (EOF) analysis of the observed SST and the model SST data sets suggest that the model is able to simulate both the decadal ENSO-like SST pattern and the North Pacific decadal SST variability found in the observations. Other ocean and atmospheric parameters associated with these SST patterns are being investigated both in the model and observations.