东海沿岸海区垂直环流及其温盐结构动力过程研究 I.环流的基本特征

DYNAMIC PROCESS OF VERTICAL CIRCULATION AND TEMPERATURE──SALINITY STRUCTURE IN COASTAL AREA OF EAST China SEA I. BASIC CHARACTERISTICS OF THE CIRCULATION

利用三维斜压流体动力学模型 ,通过对东海沿岸海区冬、夏季的斜压环流及其温盐结构的数值研究 ,揭示研究海区垂直环流及其温盐结构的动力过程及其成因。垂直环流的模拟结果表明 :冬季 ,沿岸海区的垂直环流以逆时针流动 ,近表层为向岸流 ,沿岸为下降流 ,近表层以下为离岸流 ,其在外海有明显的上升趋势 ,沿岸下降流自表层至底层逐渐由强变弱 ;夏季 ,沿岸海区的垂直环流以顺时针流动 ,近表层以下为向岸流 ,沿岸为上升流 ,近表层为离岸流 ,其在外海有明显的下降趋势 ,沿岸上升流自底层至表层逐渐由弱变强。就整个沿岸海区而论 ,冬季沿岸下降流和夏季沿岸上升流的强度都随着岸界地形坡度、风速及风向与岸线偏角的变化而变化。沿岸下降流形成的主要原因是由于冬季东北风与岸界地形的耦合效应及海区温盐分布不均匀所致 ,而沿岸上升流形成的主要原因则是由于夏季西南风与岸界地形的耦合效应及海区温盐分布不均匀所致。

Upwelling in coastal area of the East China Sea is an important phenomenon and raised extensive interests in this field. In order to understand the dynamic process and cause of vertical circulation in the area,based on real topography, surface wind stress, temperature and salinity distribution in this area, using 3D baroclinic ocean model, numerical simulations were performed for picturing vertical circulation and temperature/salinity patterns of wintertime and summertime. Results of the vertical circulation simulated are discussed in this paper. The numerical results of the vertical circulation demonstrated different patterns in wintertime and summertime. In wintertime, the vertical circulation in this area is counterclockwise, flowing shoreward in near-surface layer, downwelling in the coastal zones, and moving seaward below the surface layer with a rising tendency in outer sea. The current width of the shoreward current is narrow and its speed is strong. The current width of the seaward current is broad, and its speed is weak. The current width of the coastal downwelling is broader than that of the shoreward current and narrower than that of the seaward current. Its speed is weaker than that of the shoreward current, and is stronger than that of the seaward currents whose intensity gradually weakens with depth. In summertime, the vertical circulation there is clockwise being shoreward flow below the near-surface layer, upwelling in the coastal area, and seaward in the near-surface layer with a falling tendency in the outer sea. The current width of the shoreward current is broad, and its speed is weak. The current width of the seaward current is narrow, and its speed is strong. The current width of the coastal upwelling is narrower than that of the shoreward current and broader than that of the seaward currents. Its speed is stronger than that of the shoreward current, and is weaker than that of the seaward currents and gradually enhances from the bottom layer to the surface layer. As for whole coastal sea area, the intensity of the coastal downwelling increases gradually with increasing of continental slope, heightening of wind velocity, and decreasing of the angle between wind direction and coastline from the north to the south during the wintertime. The intensity of the coastal upwelling increases and then decreases gradually with decreasing of continental slope, increasing of wind velocity, and decreasing and then increasing of the angle between wind direction and coastline from the south to the north during the summertime. The continental slope, wind speed and the angle between wind direction and coastline influence the intensity of the coastal downwelling or upwelling, in which the angle between wind direction and coastline is a key factor for forming coastal downwelling or upwelling. The mechanism of the coastal downwelling is attributed mainly to coupling effects between the northeast wind and the coastline during the wintertime. However, the mechanism of the coastal upwelling is attributed mainly to coupling effects between the southwest wind and the coastline during the summertime.