Numerical Study On Circulation And Water Exchange In Bohai Sea With High Wind

Bohai Sea, a semi-enclosed shelf sea in the coastal China, playsimportant roles on the domestically economic development with the uniquelocation. The water in Bohai Sea is continuously deteriorating with thecoastal economy flourishing. While the marine self-purification capacitydepends on the physical dynamics. So in this paper, we focus on the impactsof the external forcing and using the ROMS model to simulate the changesof the seasonal circulation, temperature and water exchange, whichresponses to the different wind field(CFSR daily and monthly mean wind)and different topography(real and Etopo2topography).The research shows the winter current field changes obviously, whichup to6cm/s, with the change of the wind. During a strong wind in Decemberof2005,the instantaneous sea level could decreased by2m.Because of theBohai Sea prevails northwesterly wind and strong wind occurs frequentlyin winter, the winter circulation is dominated by the winter wind field.The pattern of the winter circulation driven by the strong wind,whichoccupied only25%of the total winter, is very similar to that of the wintermean. On the other hand, the structure of the summer circulation iscollectively controlled by the wind and topography. The lack of theBozhong Shoal will largely alter the coverage, shape and velocity of theclockwise circulation in this area.As the winter wind has an huge influence on the temperature, the wholepattern of the temperature changes little without the Bozhong Shoal,besides three Bay Tops slightly warming. Through the distribution oftemperature in the summer section, we find that the depth of thethermocline and the formation of the central high temperature water column are collectively controlled by the wind field and topography. The lackof the Bozhong Shoal in the topography will not form the thermocline insummer. The summer distribution of the vertical temperature will besimilar to the winter, which displays the correspondence from the surfaceto bottom. When the external forcing is daily mean wind, the central hightemperature water column will continuously exist without the tidal mixing.Thereby, when we consider the formation of the vertical distribution ofthe summer section in the Bohai Sea, as well as the tidal mixing, waveand topography (Lin et al,2006), we should also take the high spatialand temporal resolution wind field into account, especially for the mixinginduced by the strong wind.The average residence time is analyzed under the different wind fieldand topography. The result shows that the average resident time on thewhole Bohai Sea driven by the daily mean wind is smaller than that of themonthly mean wind, which is about100days and up to200days nearby theBozhong Shoal. When the Bozhong Shoal is missing in the topography, theaverage resident time will obviously decrease by up to about100days inthe middle of the sea and the Liaodong Bay. In addition, the capacity ofthe water exchange is related to the circulation to some extent.The main innovative point of this paper is firstly using thehigh-resolution wind data as the external forcing and comparing with theclimatology on circulation, temperature and average resident time.Through the comparison in our research, we find the current field, drivenby the strong wind during the spring and winter, has an essential impacton the hydrological environment inside and outside Bohai Sea. Hence, usingclimatological wind as the external forcing in the model will mislead ourunderstanding about the hydrological dynamics of the Bohai Sea.