The influence of the Three-Gorges Dam on hydrographic and hydrodynamic conditions of the East China Sea

A fine resolution model has been applied to get more insight into the effects of a modified runoff due to the Three-Gorges-Dam (TGD) on the East China Sea (ECS). The region of interest was confined to the offshore area in the vicinity of the Changjiang River. To the east, it extended up to the area southwest of Cheju Island. The model was used to evaluate the effect of a modified runoff on the water properties of the adjacent regions like the Changjiang diluted water (CDW) and the Zhoushan Fishing Ground. The sensitivity of the ECS to a modified Changjiang runoff was explored firstly by sensitivity studies and secondly by experiments based on historical runoff records and water management plans of the TGD. These experiments led to the general conclusion that the most affected area by runoff is located close to the Changjiang River mouth. The area of influence has an extension of about 150 km￡150 km. In the realistic experiment, the related anomalies reached their maximum value in early summer (May). In normal years the related salinity anomalies can get to as large as 2.     

Numerical investigation of the South China Sea deep circulation

Based on a two-level nested model from the global ocean to the western Pacific and then to the South China Sea（SCS）, the high-resolution SCS deep circulation is numerically investigated. The SCS deep circulation shows a basin-scale cyclonic structure with a strong southward western boundary current in summer（July）, a northeastsouthwest through-flow pattern across the deep basin without a western boundary current in winter（January）,and a transitional pattern in spring and autumn. The sensitivity ...     

基于TerraSAR-X卫星数据的内孤立波参数和海表流速信息提取的探索研究

本文利用TerraSAR-X(TSX)卫星于2010年4月22日在南海东沙岛附近海域获取的数据进行海洋内孤立波动力要素和海表流速信息的提取研究。基于TSX数据的后向散射强度信息,利用经验模态分解法得到内孤立波半波宽度,再利用两层模型法和参数化法计算得到内孤立波振幅和相速度。反演结果显示,利用参数化方法得到的振幅(约21～39 m)和两层模型法得到的相速度(约1.07 m/s)与历史实测资料较为一致。进而利用TSX的顺轨干涉数据获取研究海域内的多普勒速度,再分别采用M4S模型法和直接分离法处理,进而提取海表流速。结果显示,两种方法得到的海表流速的全场平均值较为一致,均为1.10 m/s左右。M4S模型法对流速最大值的改变量较大而直接分离法对流速最小值的改变量较大。M4S模型对内孤立波波峰线区域海表流速的修正大于无内孤立波的海域。最后,基于KdV方程计算得到内孤立波引起的表面流的流速约为0.28 m/s,对反演出的海表流速贡献占比23%。     

台风外围下沉区大气波导成因的数值模拟

受台风鹿莎影响,处在其西侧外围下沉区域的南京地区于2002年8月31日出现了一次大气波导过程,利用大气中尺度模式WRF对其成因进行了详细的数值模拟研究。WRF数值模拟较好地再现了此次波导的演变过程,即波导在31日傍晚开始形成,次日凌晨达到最强,日出后迅速减弱消失。基于数值模拟高时空分辨率的输出结果,对波导成因进行细致分析,结果表明:湿度突变层和逆温层的同时存在导致了波导的发生,前者是其形成的关键因素,而后者的作用主要体现在增强其强度;台风前期流场从海上带来大量的水汽,台风后期流场将北方高空干空气输送到受高压下沉运动控制的南京地区,造成近地层出现下湿上干的剧烈湿度梯度;下沉运动强度并不足以直接导致南京地区的逆温层,但其控制下的晴朗天气非常有利于夜间地面长波辐射冷却而形成逆温。     

Numerical study of current fields near the Changjiang Estuary and impact of Quick-EnKF assimilation

A 30-d current numerical simulation is running for the Yangshan Port, the Changjiang Estuary, the Hangzhou Bay and their adjacent seas using a finite volume coastal ocean model (FVCOM), with Changjiang River runoff and wind effect being considered. At the open boundary, this model is driven by the water level obtained from prediction including eight main partial tides. After the harmonic analysis, the cotidal chart and the iso-amplitude line as well as the current ellipse distribution map are displayed to illustrate the propagation property of a tidal wave. Horizontal velocity of both the U and V components coincides with the actual measurement, which shows that the model result is credible to describe the hydrodynamic pattern in this sea area. On this basis, real-time current data from high-frequency radar is assimilated with the implementation of quick ensemble Kalman filter, which takes the variation tendency of the state vector to compute the analysis field, instead of integrating the field for N (the number of ensemble) times as it used to in the standard EnKF, aiming at raising the efficiency of computation, reducing the error of prediction and at the same time, improving the forecast effect.     

基于潜标资料的中南半岛外海水文特征分析

基于2012年9月—2013年12月中南半岛外海累计16个月的长时间序列潜标观测数据,结合AVISO海表面高度异常（sea level anomaly,SLA）数据,首次详细分析了中南半岛外海典型中尺度涡的运动规律和垂向特征及其对环境水文特征的影响,揭示了该海域深层海流的时间变化特征。在观测期间共捕捉到3次中尺度涡过程,中尺度涡对站位所在海域主温跃层深度变化的最大影响振幅可达50 m。研究发现：1)观测站位所在海域各深度的温度异常时间变化与站位SLA时间变化的相关性随深度增加逐渐减弱。2)上层和中层的海水流动受中尺度涡影响显著。1 500 m和2 000 m的深层环流主要表现为季节变化;在强中尺度涡暖涡经过期间,中尺度涡能影响到1 500 m的环流场,同时出现30 d周期震荡。2 000 m流场则不受中尺度涡影响。3)中南半岛以东南海1 500 m处深层海流月平均流速夏季大于冬季,月平均可达3～5 cm·s-1;2 000 m处深层海流最大流速出现在冬季,月平均可达2～6 cm·s-1。深层海流受潮汐影响显著,潮汐作用主要影响深层海流东西向流速的变化。     

近70年胶州湾水动力变化的数值模拟研究

采用无结构三角形网格海洋模式FVCOM,基于胶州湾不同年代的岸线和水深地形条件,建立胶州湾及其邻近海域各年代的三维潮汐潮流数值模型,从数值模拟角度分析和比较胶州湾不同年代纳潮量、潮汐潮流、水交换率等水动力参数的变化。结果表明:随着胶州湾水域总面积不断缩小,纳潮量在逐渐减小,2008年全湾的纳潮量相对于1935年减少了31.5%,约合3.9×108 m3;海湾流场结构变化很小,流速呈减小趋势;胶州湾欧拉余流"团团转"的多涡结构基本保持不变,最大值都发生在团岛附近;海湾的水交换能力趋弱,对整个胶州湾水体的半交换时间进行海湾平均,不同年代5套岸线下海湾的水体半交换时间分别是37.0 d,36.7 d,39.2 d,39.7 d和40.8 d。