Upper-Ocean Heat and Salt Balances in the Western Equatorial Pacific in Response to the Intraseasonal Oscillation during TOGA COARE*

Abstract

During the TOGA COARE Intensive Observing Period (IOP) from November 1992 through February 1993, temperature, salinity, and velocity profiles were repeatedly obtained within a 130 km × 130 km region near the center of the Intensive Flux Array (IFA) in the western equatorial Pacific warm pool. Together with high quality measurements of air–sea heat flux, rain rate, upper-ocean microstructure, and penetrating solar radiation, they make up a unique dataset for upper-ocean heat and freshwater budget studies. Three survey cruises sampled different phases of the Intraseasonal Oscillation (ISO) during the IOP. Temporal evolution and advective terms in the heat and salt balance equations, on timescales of 3 days and longer, are estimated using the survey data. The upper-ocean (0–50 m) heat and salt budgets at the center of the IFA were estimated and are closed to within 10 W m−2 of observed air–sea heat fluxes and to within approximately 20% of observed rain rates during each of the three cruises. Generally, advection in the upper ocean cannot be neglected during the IOP. Zonal advection alternates sign but had a net warming and freshening tendency. Meridional advection decreased temperature and increased salinity in the surface layer, while vertical advection warmed and freshened the surface layer because of the general downwelling trend. Heat advection is as important as the net air–sea flux during the westerly wind burst time periods. The sub-ISO timescale upper-ocean dynamics, such as the strong meridional advection caused by inertial motions, are found to have important contributions to the upper-ocean heat and freshwater balances.