Model diagnostic study of cross-shelf flow in the northern South China Sea

基于POM诊断模型，利用GDEM、WOA13和SCSTS气候态温盐数据，对南海环流作诊断计算。根据三套数据诊断结果在南海的气候态流场，剖析南海北部跨陆坡运动的特征，并探讨其动力机制。结果表明，南海北部存在跨陆坡运动，且具有明显的空间分布特征：水平结构上，陆坡海区广泛分布跨陆坡运动，并以向陆架方向运动为主，且随陆坡地形呈现不均匀分布；垂向结构上，沿200 m、500 m和1000 m等深线断面的跨陆坡运动垂向分布，均存在多处向陆架方向的强跨陆坡运动中心。为了解陆架与外洋的水交换，估算此三个沿等深线断面的跨陆坡体积输运，并进一步估算其热盐含量输运。沿200 m和500 m等深线断面主要表现为向陆架方向的跨陆坡输运，而1000 m等深线断面主要表现为向外洋方向的跨陆坡输运，且在量值上前二者大于后者。跨陆坡运动伴随着热盐输运，大量的热量和盐分向近岸输送，而少量向外洋输送。根据动量平衡分析发现，陆坡环流较好地满足地转平衡关系，其中沿陆坡运动占主要部分，跨陆坡运动约占15-20 %。并且跨陆坡运动或沿陆坡运动主要受压强梯度力和科氏力的调控，同时受地形梯度的影响。Model diagnostic method is utilized in the South China Sea with a regional, three-dimensional, primitive equation model (POM). The climatological temperature and salinity data of GDEM, WOA13, and SCSTS are applied in the diagnostic calculation. The diagnostic results from three data sources agree well with the observations in sea surface height, and reflect the remarkable spatial distribution of the cross-shelf flow in the northern South China Sea. The cross-shelf flow is active in the continental slope region, and it flows towards to the shelf. The cross-shelf flow indicate a uniform structure in horizontal direction between 200 m and 2000 m isobaths. The cross-shelf velocity has several local maximum along the shelf direction in different sections. The estimation of the cross-shelf volume transport explain that, the cross-shelf volume transport in the 200 m and 500 m isobath is towards the shelf direction, and that of the 500 m and 2000 m isobath is in the opposite way. Therefore, much heat and salt contents is transported towards the shelf region, and a small amount come down off the slope region. With the analysis of momentum balance we found that, the along-slope flow is primary in the two components of slope current, and the cross-shelf flow is minor component, it is about 15-20 % of the slope current. The cross-shelf flow is mainly controlled by the pressure gradient and Coriolis force in the momentum balance analysis, simultaneously it is affected by the gradient of topograph