Study On Characteristics And Effect Factors Of Storm Surges In Bohai Sea

Bohai Sea is the only inland sea in China and its coastal area is economically developed and densely populated.Due to geographical factors,Bohai Sea is often affected by weather processes like strong wind or extratropical cyclone which may cause severe storm surges and it is one of the areas where storm surges occur frequently.In order to protect people's lives and property in this area,it is necessary to get a thorough understanding on characteristics of storm surges and develop a prediction model so that relevant department could forecast and mitigate storm surge disasters effectively and take essential guard measures.Storm surges can be influenced by several factors,such as geography,meteorology,astronomical tides and surface waves.Characteristics of different kinds of storm surges are also different.Based on large amount of data,the storm surges in Bohai Sea can be divided into four main types:Cold front fit low pressure,Cold front,Strong extratropical cyclone and Typhoon.Combine the finite-volume coastal ocean model FVCOM and the wave mode SWAN to simulate four typical storm surge processes.The features of set-up caused by wind,air pressure,waves and topography were also analyzed.Verify wind field data from the National Center for Environmental Prediction(NCEP)and the European Center for Medium-Range Weather Forecasts(ECMWF)with the measured one respectively,and choose the NCEP data for its better conformity.Establish a wave-current coupled model based on the collected basic data like topographic,coastline,hydrological and meteorological data.The computational domain is covered the whole Bohai Sea and the northern Yellow Sea.The coupled model is calibrated and validated with the measured data.The results show that the model can be used for subsequent research.Numerical simulations of four typical storm surge processes in Bohai Sea were carried out by using the coupled model.The results show that the effect of air pressure in Cold front storm surge process is not obvious compared with the Cold front fit low pressure process.The moving path of the low-pressure center plays an important role in the Strong extratropical cyclone and Typhoon process.Wind is the most important factor of storm surges,while waves' influence cannot be ignored as well.If the effect of waves on sea surface roughness is not considered in numerical simulation,the extreme value of set-up could be underestimated.Coastal currents caused by wave breaking in the shallow coastal area(such as the southwest of Bohai Bay,Laizhou Bay,the north of Liaodong Bay and the east of Caofeidian port)could cause tiny amounts of set-up.The direction of wave induced longshore current in the surf zone of southwest Bohai Bay is clockwise.This current has an obvious shoreward trend on the sea surface and an unobvious shoreward trend at the bottom.Outside the surf zone,the wave induced current direction is offshore on the sea surface and shoreward at the bottom with a lower velocity.