El Nino-Southern Oscillation sea surface temperature and wind anomalies, 1946-1993

Abstract

El Nino-Southern Oscillation 9ENSO) periods, which occur irregularly every few years, are a major perturbation of the Earth's climate system that involves large-scale changes in winds, rainfall, sea surface temperature (SST), and surface pressure. In some areas of the world there are disastrous droughts, and in others there is serious flooding. North American weather patterns are also affected. It is important to develop skillful forecasts for ENSO periods. Our goal here is to provide an overview of the globval ocean and atmosphere surface changes that typically occur during ENSO periods. Knowledge of these anomaly patterns is needed in order to improve our understanding and forecasts of ENSO. With a global surface data set we describe the statistically significant patterns of SST, surface wind, and surface pressure changes that on average are associated with the 10 post-World War II ENSO periods. We present these average anomaly results as an 'ENSO composite.' It is useful to identify phases of the tupical ENSO and examine the statistically significant elements phase by phase. An ENSO by ENSO period search indicates that about two thirds of these elements occur in 90% or more of the ENSO periods: we define a 'Robust ENSO Composite' from these frequently occurring elements and find it to be an Indo-Pacific phenomenon. Limitations in the surface data set make it possible that this study has not identified all the important aspects of ENSO periods; data are very sparse in both space and time over much of the tropics and the southern hemisphere. However, we suggest that any theory or model of ENSO should at least exhibit the features of this robust composite, and is unlikely to able to represent adequately the large-scale environmental impacts of ENSO unless it does so.