Investigation of storm surges over the Pearl River Estuary during typhoon No. 9316 using a Nested-Grid Coastal Circulation Model
【摘要】：The Pearl River Estuary (PRE) is a sub-tropical estuary with highly irregular topography and dynamically complicated circulations and hydrographic distributions. Astronomical high tide, storm surge and rainstorm make typhoon No. 9316 one of the most destructive tropical cyclones to impact the China coast. In this study, a nested-grid coastal circulation modelling system is used to examine the storm surge over the PRE during typhoon No. 9316. Based on the Princeton Ocean Model (POM), the nested-grid system consists of a coarse-resolution outer model over China Seas from Bohai Sea to the northern South China Sea, a medium-resolution middle model of the northern South China Sea, and a fine-resolution inner model of the PRE. The modelling system is forced by tides, meteorological forcing and buoyancy forcing associated with freshwater runoff from the Pearl River system. The verification and the parameter calibration are made with the field measured data of the tidal level process, the sea surface temperature and salinity distributions during both the summer and the winter (Tang et al., Ji et al.[2-3]). The nested-grid system is then used to simulate the tidal level changes, and the horizontal and vertical distributions of currents over the PRE and adjacent coastal waters during typhoon No. 9316. The tidal level in the adjacent coastal waters is mainly influenced by the non-linear effect of the typhoon and the tides. The tidal level rises during higher high tide and lower low tide, while drawdown during higher low tide and lower high tide. The larger the tidal range, the more obvious the diurnal inequality. The tidal level near the river inlets is not only influenced by the non-linear effect of the typhoon and the tides, but also affected by the shallow water topography, the freshwater runoff and the complicated coastlines, especially in the Modamen, Yamen and Hongqimen inlets. The strong wind during the typhoon period causes dramatic changes of the velocity fields over the sea surface, and lead to corresponding anti-clockwise cyclonic circulation. In the Lingding Bay, vertical circulations are generated while the northwest rotating airflow encounters the southeast currents. The vertical circulations increase the vertical mixing effects, and the sea surface currents become smaller, then the water accumulates, and the worst adverse storm surge is formed under the combined effect of strong typhoon wind, freshwater runoff and high tides.