Process Study of Dry-Season Circulation in the Pearl River Estuary and Adjacent Coastal Waters using a Triple-Nested Coastal Circulation Model

Abstract

The Pearl River Estuary (PRE) on the east coast of Guangdong Province in South China is a complicated hydrodynamic system affected by various forcing functions including tides, wind forcing, and sea surface heat and freshwater fluxes. The PRE also receives a large amount of freshwater runoff from the Pearl River through eight major river inlets. In this study, the three-dimensional circulation, hydrography, and associated temporal variability in the PRE and adjacent coastal waters during the dry season from December to March are examined using a triple-nested coastal ocean circulation modelling system based on the Princeton Ocean Model. Four numerical experiments are conducted by driving the triple-nested modelling system with different combinations of external forcing functions. Analysis of multi-year model results from the four experiments demonstrates that the estuarine plume in the dry season is close to the western shore of the PRE, mainly due to the combination of the low Pearl River discharge and the influence of the southwestward coastal current over the inner shelf of the northern South China Sea. Temperature and salinity inside the estuarine plume in the dry season are weakly stratified in the vertical, with large horizontal salinity gradients near the frontal zone of the plume. Baroclinic dynamics play a very important role in the plume, with the frontal circulation forced by the combination of wind, tides and the Pearl River discharge. In the offshore deep waters of the PRE during the dry season, vertical stratification in the top 15 m is weak and circulation can be approximated by barotropic dynamics forced by wind and tides.