Upper Ocean Sensitivity to Wind Forcing in the South China Sea

The Naval Research Laboratory (NRL) Layered Ocean Model (NLOM) has been used to investigate the sensitivity of the upper South China Sea (SCS) circulation to various atmospheric wind forcing products. A 1/16° 6-layer, thermodynamic Pacific Ocean north of 20°S version of NLOM has been integrated using observed climatological monthly mean winds (Hellerman and Rosenstein, 1983) and climatologies based on two atmospheric prediction models: the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP). ECMWF products include the 10 meter winds (at both 1.125° and 2.5° resolution) and surface stresses (1.125°). The NCEP forcing (1.875°) is a surface stress product. Significant differences exist in the wind stress curl patterns and this is reflected in the upper ocean model response, which is compared to observational data. The model experiments suggest the generation of the West Luzon Eddy is controlled by positive wind stress curl. The degree of Kuroshio intrusion into the SCS, however, is not affected by wind stress curl but is governed by the coastline geometry of the island chain within Luzon Strait. The summertime offshore flow from the Vietnamese coast is present in all simulations but the dipole structure on either side of the jet is variable, even among experiments with similar wind stress curl patterns. The ECMWF surface stresses exhibit spurious coastal wind stress curl patterns, especially in locations with significant orographic features. This manifests itself in unrealistic small scale coastal gyres in NLOM. High resolution basin-scale and coastal models might be adversely affected by these stresses.