Impact of tides and winds on estuarine circulation in the Pearl River Estuary

The Finite-Volume Coastal Ocean Model (FVCOM) is used to simulate the dynamics of the circulation in the Pearl River Estuary (PRE), validated against the in-situ measurements of a cruise survey. The model simulation agrees well with observed sea level at local tide gauge stations and reproduces observed characteristics of the currents. A simplified model run without wind forcing reveals that there is a significant spring-neap variation in the along-estuary circulation. Additional sensitivity runs that include up-estuary and/or down-estuary winds are also implemented. These results reveal that the cross-estuary adjustment of stratification and mixing induced by along-estuary winds is stronger than the along-estuary wind straining effect; these yields enhanced stratification and weakened mixing under the up-estuary wind. During spring tide, the response of the along-estuary circulation to the along-estuary wind forcing is weak, while during neap tide, the up-estuary and down-estuary winds may induce substantial variations in the along-estuary circulation. The analysis on the momentum budget and turbulent stress reveals the different dynamic response of the estuarine circulation in the PRE to different wind forcing conditions, identifying a significant modification to estuarine circulation by the wind-tide interaction.