Satellite Observations of Upper-Layer Variabilities in the Western Pacific Warm Pool

Abstract

The variabilities of the upper layer of the western Pacific warm pool (WPWP) were observed using satellite infrared data from 1982 to 1991 and altimeter data from November 1986 to September 1989. The warm pool was defined as the area where the sea surface temperatures are above 28°C. The eastern boundary oscillation, the centroid movement, and the upper-layer volume variation of the WPWP were intensively studied. Spectral analysis revealed that the eastern boundary osciilation of the WPWP was related to the El Niño event and the annual cycle. The centroid of the WPWP traced an ellipselike trajectory during a year and moved counterclockwise in most years. However, in 1982 and 1986, the years of the onset of El Niño events, the movements were clockwise. The upper-layer volume of the WPWP was divided latitudinally into three sections. The annual cycles in the northern (from 3° to 30°N) and southern (from 3° to 30°S) sections were dominant. No annual cycle was found in the equatorial section (from 3°S to 3°N), but the volume of warm water in the equatorial Pacific increased during the 1986/87 El Niño event. The equatorial section was further divided into eastern and western sectors along 165°W. During the 1986/87 El Niño event, the volume of warm water increased in the eastern sector, but the variation was smaller in the western sector than that in the eastern sector. During the 1988 La Niña event, the warm water volumes decreased in both sectors.