Basin-Wide Zonal Wind Stress and Ocean Thermal Variations in the Equatorial Pacific Ocean

Wind data, obtained from the model results of the European Centre for Medium Range Weather Forecasts (ECMWF), for the equatorial Pacific Ocean from 1985 to 1992, were employed to study the basin-wide distributions for various constituents of zonal wind stress. Forcing the ocean by the individual constituent of zonal wind stress, the upper ocean thermal variation was investigated using a linear analytical ocean model. The interannual variation of zonal wind stress is largest in amplitude in the west-central part of the basin and is dominated by an eastwardly propagating wave. The upper layer thickness perturbation h shows an evolving eastward propagation over the region where the interannual wind stress variation occurs, while to the east and west the region changes nearly in phase. The evolution of h agrees well with the evolution of upper ocean heat content anomaly, estimated from the Tropical Atmosphere-Ocean (TAO) moored array. The annual cycle of zonal wind stress can be described properly by a combination of annual and semiannual variations. The annual variation of zonal wind stress was found to propagate westward with relative maxima out of phase to the west and east of the west-central Pacific. The semiannual variation is stationary and is largest in amplitude in the western basin. Forced by the two components of the annual cycle of zonal wind stress, the evolution of h shows a westward propagation. This does not correlate well with the pattern of the evolution of the annual cycle of upper ocean heat content which emanates from the east-central Pacific and shows both eastward and westward propagation. The seemingly anomalous eastward propagation is mainly related to the abrupt change during the relaxation/intensification period of the easterly wind stress. The abrupt change of the annual zonal wind stress variation in both time and space is, then, critical for the evolution of the pattern of the annual ocean response