lEI Nino-Southern Oscillation Displacements of the Western Equatorial Pacific Warrn Pool." Science 250

The western equatorial Pacific warm pool (sea-surface temperatures>29"C) was observed to migrate eastward across the date line during the 1986-1987 El Niño-Southern Oscillation event. Direct velocity measurements made in the upper ocean fiom 1986 to 1988 indicate that this migration was associated with a prolonged reversal in the South Equatorial Current forced by a large-scale relaxation of the trade winds. The data suggest that wind-forced zonal advection plays an important role in the thermodynamics of the western Pacific warm pool on interannual time scales. HE SOUTHERN OSCILLATION IS A large-scale seesaw in atmospheric T pressure between the eastem sub-tropical Pacific and the maritime land mass-es of Australia and Indonesia ( 1,Z). Pressure differences between these two regions drive easterly trade winds, which are the principal forcing function of tropical ocean circula-tion. The trade winds converge in the west-ern Pacific in regions of deep atmospheric convection and high rainfall rates. A drier air mass then retums eastward aloft before de-scending in the subtropical high region of the eastern Pacific. Periods when the pres-sure is unusually high in the west.and low in the east are associated with EI Niño, an oceanic phenomenon characterized by weakened trade winds in the central and western Pacific and sea-surface temperatures (SSTs) that are warmer than usual from the coast of South America to west of the date line (3). EI Niñdouthern Oscillation (ENSO) episodes occur on an irregular cy-de of about 2 to 10 years, the most recent of which occurred in 1986 to 1987 (4, 5). Although the origins of ENSO may be traced to the tropics, its manifestations are felt worldwide through disruptions in the atmospheric general circulation and associ-ated weather pattems (1, 6). The westem Pacific warm pool, defined by SSTs> 29"C, has recently taken on