| The Yangtze River Estuary and its adjacent waters are one of the key water areas for the study of coastal interactions in my country.The Yangtze River Dilute Water has an important impact on the hydrological and ecological environments of the Yellow Sea and the East China Sea.Therefore,studying the mixing characteristics of the water in the Yangtze River Estuary is important for understanding the Yangtze River Dilute Water the transportation of nutrients and pollutants carried has important scientific significance and economic value.This thesis uses the winter observation results from March 3 to March 14,2019 and the summer observation results from July 11 to July 17 in the Yangtze River Estuary and its adjacent waters to obtain the two seasons.Results of temperature and salt distribution characteristics and turbulence distribution characteristics.In winter,the isotherms of the four sections in the range of 122.2°-123°east longitude are arc-shaped,and the isotherms are almost perpendicular to the sea surface at 123°-124°east longitude.In winter,the vertical distribution of salinity is relatively uniform,and the Yangtze River Dilute Water with a salinity less than 32 is restricted to the west of 123°E.The dilute water of the Yangtze River is affected by the north wind in winter,and the influence of the dilute water of the Yangtze River on salinity is limited to the narrow strip near the coast,while other waters show a state of fully mixed salinity,which is consistent with the temperature distribution characteristics.The turbulent energy dissipation rate of section A8 in winter varies between 10-7-10-10W/kg,and the turbulent energy dissipation rates of the other three sections are all around 10-10W/kg,and the four sections are averaged from north to south.The turbulent energy dissipation rate gradually increases,and the turbulent diffusion coefficient is the smallest near the shore.The water body stratification in the study area is obvious in summer,and the thickness of the halocline gradually decreases from north to south,and the intensity weakens.The upwelling process inside the frontal zone strengthens mixing and leads to the detachment of the low salt water mass.In summer,the vertical turbulent diffusion coefficients of the four sections are larger in the surface layer,and decrease with the increase of water depth.In summer,there is an upwelling current in the observation sea area,and the turbulent energy dissipation rate is relatively large in the areas where upwelling and downflowing currents exist.The runoff of the Yangtze River in summer is significantly higher than that in winter,but the concentration of surface nutrients in summer is lower than that in winter.This is because the concentration of surface chlorophyll a is the largest in summer,and the strong photosynthesis makes phytoplankton uptake a lot of nutrients.This thesis conducted a 25-hour continuous observation in the waters near the Yangtze River Estuary at 122.814°east longitude and 30.741°north latitude from July 26 to July 27,2019,and found that the temperature during the entire observation day gradually decreased from top to bottom,and the salinity Increase with the increase of water depth.The shear of the vertical velocity caused by the tidal current throughout the observation day promotes turbulent mixing.The existence of the cline limits the intensity of turbulent mixing at this depth and limits the vertical transport and mixing process of the water body.This thesis finds that in the sea area driven by strong tides,strong tidal currents will cause greater energy dissipation in the bottom boundary layer.As the height of the tidal current increases from the bottom of the sea,the turbulent energy dissipation rate and vertical turbulent diffusion coefficient and other parameters will gradually decrease.The short-period cline disturbance caused by the internal wave process that may exist in the observation area promotes the vertical mixing at the cline. |
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