On the Structure of the Southern Oscillation

Abstract

A realistic oceanic general circulation model is forced with winds observed over the tropical Pacific between1967 and 1979. The structure of the simulated Southern Oscillation is strikingly different in the western andeastern sides of the basin, because the principal interannual zonal-wind fluctuations are confined to the westand are in the form of an equatorial jet. This causes thermocline displacements to have maxima offthe equatorin the west (where the curl of the wind is large) but on the equator in the east. Zonal phase propagation, bothon and offthe equator, is at different speeds in the west and east. The phase pattern is complex, and there is,on interannual time scale, no explicit evidence ofindividuai equatorial waves. These results lead to a modificationof the "delayed oscillator" mechanism originally proposed by Schopfand Suarez to explain a continual SouthernOscillation. The results also permit an evaluation of the various coupled ocean-atmosphere models that simulatethe Southern Oscillation and indicate which measurements are necessary to determine which models are most- relevant to reality.