Surface salinity budget in oceanic simulation using data from TOGA COARE

Abstract

A three‐dimensional regional model is used to investigate the role of different terms of the salinity budget in the western Pacific during TOGA COARE. The model is a version of the ocean general circulation model (OGCM) developed at the Laboratoire d'Océanographie Dynamique et de Climatologie (LODYC) in Paris and includes open lateral boundaries and a 1.5‐level‐order turbulence closure scheme. The surface atmospheric forcing used, including water flux, comes from a combination of European Center for Medium‐Range Weather Forecasts model output and estimates from bulk parameterization. The data set collected during the Intensive Observation Period enables the initialization, taking into account the lateral boundary conditions, and validating the model outputs. Different atmospheric weather conditions were experienced during the simulation of the variability of the mixed layer. During 25 days, air‐sea fluxes were downward, that is precipitation exceeds evaporation, and increasing with time. In periods of weak winds (December 2–12), strong solar radiation, and shoaling of the oceanic mixed layer, the entrainment is negative and salt is removed from the oceanic mixed layer. Mixed layer currents are low and slightly divergent from the equator toward the south with a mean eastward component. Due to the zonal advection, there is a freshening tendency in the north of the domain. In periods of strong winds (December 21–27) and reduced solar radiation, the oceanic mixed layer is deepening and entrainment is positive and contributes to the salinity increase. The salinity storage term is quite inhomogeneous during the two periods as a consequence of the patchy pattern of advection. Moreover, most of its temporal and spatial variability is strongly correlated with the temporal and spatial variability of the advection term. Currents are largely converging toward the equator and create a band of saltier water in the surface layer.