Tropical Pacific ENSO cold events, 1946-95: SST, SLP, and surface wind composite anomalies

ENSO cold (La Nina) events are shown to exhibit a distinctive life cycle. T he first near-global description of ENSO cold (La Nina)-event anomaly featu res is described using ocean surface data. It is found that cold-event anom alies are not simply the mirror image of warm (El Nino) events. The Compreh ensive Ocean-Atmosphere Data Set marine surface record [SST, sea level pres sure (SLP), and wind] is used to identify the statistically significant fea tures of the nine cold-event periods during 1946-95 and to focus on the lar ge-scale elements that are typical of most events. By examining time series , the most robust features of the composite that have occurred during nearl y all of the post-World War II cold events are identified. These robust cold-event features are more numerous and cover more of the gl obe than their warm-event counterparts. Of the 90 composite features examin ed, 57 (63%) are found to be robust. Most of these are located in the Tropi cs (70%) and in the Pacific (65%). However, robust elements are found in al l the ocean basins (Indian-14%; Atlantic-21%) and in both hemispheres (Nort hern-18%; Southern-12%), making cold events truly global. In addition, a tr ue life cycle for the cold event is found, with different anomalies occurri ng at different phases of the evolution of the event and not just during th e peak (largest amplitude) phase. The evolution and simulation of these cha racteristic features of cold events offer as important a challenge to coupl ed models as the more familiar warm-event anomalies.