SATELLITE-OBSERVATIONS OF UPPER-LAYER VARIABILITIES IN THE WESTERN PACIFIC WARM POOL

The variabilities of the upper layer of the western Pacific warm pool (WPWP) were observed using satellite infrared data from 1982 to 1991 a nd altimeter data from November 1986 to September 1989. The warm pool was defined as the area where the sea surface temperatures are above 2 8 degrees C. The eastern boundary oscillation, the centroid movement, and the upper-layer volume variation of the WPWP were intensively stud ied. Spectral analysis revealed that the eastern boundary oscillation of the WPWP was related to the El Nino event and the annual cycle. The centroid of the WPWP traced an ellipselike trajectory during a year a nd moved counterclockwise in most years. However, in 1982 and 1986, th e years of the onset of El Nino events, the movements were clockwise. The upper-layer volume of the WPWP was divided latitudinally into thre e sections. The annual cycles in the northern (from 3 degrees to 30 de grees N) and southern (from 3 degrees to 30 degrees 5) sections were d ominant. No annual cycle was found in the equatorial section (from 3 d egrees S to 3 degrees N), but the volume of warm water in the equatori al Pacific increased during the 1986/87 El Nino event. The equatorial section was further divided into eastern and western sectors along 165 degrees W. During the 1986/87 El Nino 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 Ni na event, the warm water volumes decreased in both sectors.