Abstract
ENSO cold (La Niña) events are shown to exhibit a distinctive life cycle. The first near-global description of ENSO cold (La Niña)–event anomaly features is described using ocean surface data. It is found that cold-event anomalies are not simply the mirror image of warm (El Niño) events. The Comprehensive Ocean–Atmosphere Data Set marine surface record [SST, sea level pressure (SLP), and wind] is used to identify the statistically significant features of the nine cold-event periods during 1946–95 and to focus on the large-scale elements that are typical of most events. By examining time series, the most robust features of the composite that have occurred during nearly all of the post–World War II cold events are identified.
These robust cold-event features are more numerous and cover more of the globe than their warm-event counterparts. Of the 90 composite features examined, 57 (63%) are found to be robust. Most of these are located in the Tropics (70%) and in the Pacific (65%). However, robust elements are found in all the ocean basins (Indian—14%; Atlantic—21%) and in both hemispheres (Northern—18%; Southern—12%), making cold events truly global. In addition, a true life cycle for the cold event is found, with different anomalies occurring at different phases of the evolution of the event and not just during the peak (largest amplitude) phase. The evolution and simulation of these characteristic features of cold events offer as important a challenge to coupled models as the more familiar warm-event anomalies.
Corresponding author address: Narasimhan K. Larkin, NOAA/PMEL, Bldg. 3, 7600 Sand Point Way NE, Seattle, WA 98115. Email: larkin@pmel.noaa.gov
* Joint Institute for the Study of the Atmosphere and Ocean Contribution Number 851 and Pacific Marine Environmental Laboratory Contribution Number 2638.
