Characteristics of the Response of Sea Surface Temperature in the Central Pacific Associated with Warm Episodes of the Southern Oscillation

Abstract

The zonal distribution of sea surface temperature (SST) in the equatorial Pacific (4°N-4°S, 120°E-80°W) associated with El Niño/Southern Oscillation (ENSO) has been studied by using the seasonal mean file of the Comprehensive Ocean-Atmosphere Data Set (COADS) for the period 1940 to 1983. Although the warmest ocean area in the western central Pacific exhibits very little annual variation, it is very sensitive to the ENSO, displaying large variability during such episodes. The eastward migration of this warmest area (28.5°C isotherm is used here as a criterion related to strong tropical convection and heavy rainfall) is a common feature in the developing stage of almost all ENSO events since 1940, not only for the event of 1982. The extent of its eastward migration varies from event to event and represents a large contribution to the interannual variability of zonal SST distribution in the equatorial Pacific, comparable to the behavior of the equatorial cold tongue in the east The spread of the warmest water constitutes an active factor in the development of ENSO events. Analysis of zonal profiles of SST in this area shows two major patterns. The first pattern is warm in the east and central areas and slightly below normal in the west (1972 type ENSO). A second pattern is characterized by the presence of nearly uniformly warm anomalies in the entire area (1963 type ENSO). A third, which occurred only in 1976, is warm in the east, normal in the central, and slightly below normal in the west. These three patterns account for 62% of the total equatorial Pacific SST variance about the mean seasonal profile. The patterns of SST profile mainly depend on the relative contribution of the warmest water in the west-central Pacific and the equatorial cold tongue in the east. The west-to-east SST gradient in these three profile patterns is appreciably different, which could prove useful in distinguishing ENSO types in the future.