El Niño events and their relation to the Southern Oscillation: 1925–1986

Abstract

Relationships among sea surface temperatures (SSTs) at the coast of Peru and offshore, river discharge in northern Peru, and sea level pressure at Darwin, Australia, during the period 1925–1986 are investigated using time series plots, frequency distributions, and a simple statistical analysis. It is shown that SSTs undergo a larger seasonal cycle offshore than at the coast, exhibit more interannual variability during the warm than the cool season, are positively skewed during much of the year, and exhibit greatest month‐to‐month persistence during the cool season. Many, but not all, episodes of above normal coastal SSTs are accompanied by enhanced river discharge in northern Peru. Comparison of the Darwin pressure and coastal SST records during the past 60 years shows that El Niño events (episodes of above normal SSTs along the coast of Peru) have occurred both in advance of and subsequent to major negative swings of the Southern Oscillation (and associated climatic changes in the central equatorial Pacific). In addition, El Niño events and negative swings of the Southern Oscillation have occurred separately. Hence El Niño and the Southern Oscillation are more loosely coupled than other studies would imply.