El Ni？o-Southern Oscillation (ENSO) is the dominant mode of variability in the tropical Pacific at interannual timescales, and has a widespread effect on the global climate system. Numerous previous studies have suggested a physical connection between intrinsic atmospheric variability over the North Pacific in a particular boreal winter and ENSO in the following boreal winter. However, until now, few investigations have examined Southern Hemisphere influences on ENSO. 

Scientists from Institute of Atmospheric Physics (IAP) found that the Pacific-South American (PSA) pattern of the South Pacific extratropical sea level pressure (SLP) anomalies may also have an additional influence on ENSO. Their study demonstrates that the influences of extratropical atmospheric variability in the South Pacific and North Pacific on ENSO are different and relatively independent. It is possible that they may, together or separately, influence the occurrence of ENSO events, and the importance of the South Pacific forcing in initiating ENSO events is comparable with that of the North Pacific forcing. An empirical model was established to predict the Ni？o3.4 index based on the combined South Pacific and North Pacific signals, and results show that it can be used to produce skillful forecasts of the Ni？o3.4 index with a leading time of up to 1 yr.