Effects of Temperature and Salinity on Surface Currents in the Equatorial Pacific

Abstract

AbstractSurface currents in the equatorial Pacific play a key role in determining thermohaline structures in the upper ocean, thus acting to modulate the tropical Pacific mean state and interannual variability. In turn, the thermohaline structure and its variability can also affect surface currents by changing ocean density and pressure gradients. Currently, the thermohaline effects on the surface currents have not been well understood, especially for the salinity role. In this study, the thermohaline effects on surface currents in the equatorial Pacific are systematically evaluated based on an analytical scheme, which is used to calculate surface currents in producing the Ocean Surface Current Analysis Real‐time (OSCAR) product. Several calculations are performed with the original OSCAR‐based scheme and an improved scheme including the salinity effect. It is demonstrated that the thermohaline effects are generally dominated by the temperature role, but the salinity effect plays a non‐negligible role near the dateline and in the far eastern Pacific. The thermohaline effects are quantified and highlighted on seasonal and interannual time scales. For annual mean surface currents, temperature and salinity effects work together to weaken zonal currents north of the equator, with their reduced amplitude by about half. Seasonally, the thermohaline effects are dominant in spring due to the weakened wind effect. Interannually, the salinity effect explains up to 25% of the total variance in the far eastern equatorial Pacific. This study highlights the substantial contributions of thermohaline anomalies to surface current variabilities, in which salinity can play an important contributing role.