A Study of the Southern Oscillation and Walker Circulation Phenomenon

A survey of the literature dating back to the early 1920’s along with some appropriate statistical studies delineate an atmospheric-oceanic phenomenon of considerable interest. The Southern Oscillation—an oscillatory exchange of atmospheric mass between the eastern south Pacific and Indonesia—and the Walker Circulation—its counterpart in wind circulation—have a time-scale of years and are manifestations of a near-global variation in circulation, clouds and precipitation, centered in the equatorial eastern Pacific. Ocean surface temperatures in this region are intimately involved; in their warmest phase these variations are known as El Niño events. Some evidence that the strength of the Northern Hemisphere subtropical jet stream varies in conjunction with this phenomenon is given. Since a fully coupled atmosphere-ocean model is presently impractical, a set of general circulation model experiments using altered ocean boundary temperatures has been performed with the NCAR 5° global atmospheric model. Simulation of the phenomenon was successful in that many of the observed atmospheric variations are reproduced. A relative, thermally direct circulation is produced which is driven principally by the latent beat of condensation. The interaction between the dynamics and thermodynamics is underscored since atmospheric response to increased ocean surface temperatures occurs westward of the largest temperature increases, and the subtropical jet stream north of the prescribed change is significantly affected. While the results of this modeling study do not completely illuminate the problem of atmosphere-ocean interaction as a closed-loop feedback process on these annual time scales, they do suggest where the more important areas for future research must lie.