Process study of circulation in the Pearl River Estuary and adjacent coastal waters in the wet season using a triply-nested circulation model

A triply-nested coastal circulation modelling system is used in examining hydrodynamic responses of the Pearl River Estuary (PRE) and adjacent coastal waters of the South China Sea to tides, atmospheric forcing and freshwater runoff from the Pearl River during the wet season from May to August. The triply-nested coastal modelling system consists of a coarse-resolution outer model for simulating the two-dimensional tidal and wind-driven circulation over the China Seas of the northwest Pacific Ocean; an intermediate-resolution middle model for the three-dimensional (3D) simulating shelf circulation over the inner shelf of the northern South China Sea; and a fine-resolution inner model for simulating the 3D estuarine circulation over the PRE and adjacent coastal waters. Four numerical experiments are conducted by driving the triply-nested modelling system with different combinations of external forcing. Analysis of model results in the four experiments demonstrates that a large-size estuarine plume occupies the PRE during the wet season. The wet season mean circulation in the PRE is characterized by a two-layer estuarine circulation in the vertical, with a sharp salinity front near the mouth of the Estuary. In the deep waters off the PRE, the wet season mean circulation is affected by the large-scale, northeastward coastal current forced primarily by wind forcing. Model results are also used in examining the main physical processes affecting the daily and synoptic variability of circulation over the PRE and adjacent waters.