Three-dimensional structure of tidal current in the East China Sea and the Yellow Sea

A three-dimensional tidal current model is developed and applied to the East China Sea (ECS), the Yellow Sea and the Bohai Sea. The model well reproduces the major four tides, namely M₂, S₂, K₁ and O₁ tides, and their currents. The horizontal distributions of the major four tidal currents are the same as those calculated by the horizontal two-dimensional models. With its high resolutions in the horizontal (12.5 km) and the vertical (20 layers), the model is used to investigate the vertical distributions of tidal current. Four vertical eddy viscosity models are used in the numerical experiments. As the tidal current becomes strong, its vertical shear becomes large and its vertical profile becomes sensitive to the vertical eddy viscosity. As a conclusion, the HU (a) model (Davieset al., 1997), which relates the vertical eddy viscosity to the water depth and depth mean velocity, gives the closest results to the observed data. The reproduction of the amphidromic point of M₂ tide in Liaodong Bay is discussed and it is concluded that it depends on the bottom friction stress. The model reproduces a unique vertical profile of tidal current in the Yellow Sea, which is also found in the observed data. The reason for the reproduction of such a unique profile in the model is investigated.     

2004年东海及黄海部分海域表层水温分布状况

分析了2004年东海及黄海部分海域表层水温的分布状况,结果表明,不同水团具有不同的温度年变化,大陆水系的均极差远大于多年平均值,说明沿岸海域的表层水温该年变化比常年大,但黑潮主干区的均极差却比多年平均值低;夏季沿岸海域以及中间水域出现了异常的高温现象,在8月,浙江沿岸、江苏沿岸、长江口以及福建部分沿岸海域的表层水温都突破了近20年的历史最高纪录;在春末、秋末沿岸海域表层水温远高于多年平均值.在暖流区域,除冬季的表层水温高于常年外,其它时间与多年平均差不多,所以年变化相对较小.     

渤海、黄海、东海冬季海流场温度场数值模拟和同化技术

利用NASA高分辨率的卫星遥感资料SST,采用Nudging同化来模拟渤海、黄海、东海的三维温度场,减小用热通量作上边界条件所带来的误差.结果表明,模拟的海流场能较好地反映渤海、黄海、东海的环流特征.数据同化后的温度场优于未经同化的温度场.3个选择站点的同化值与实测值的均方根误差分别为1.307,0.526,0.744,用热通量资料模拟的水温与实测值的均方根误差分别为2.160,0.979,1.330.尽管只同化了海表温度,但数据同化对三维温度场结构都有影响.     

Derivation of sea surface current field from sequential satellite images of the East China Sea

ThisprojectwassupportedbytheGermanMinistryofScienceandTechnology(BMFTBEO/7103F0016A)andtheStateOceanicAdministration,China.INTRoDUCTIONTheEastChinaSea,withanaveraged5oOkmcontinentalshe1f,containslargeamountofnaturalresourcesandfishinggrounds.ThewarmandsalineKuroshiowhichoriginatesfromtheNorthEquatorialCurrentintrudesintothisarea.ManylargeriverssuchastheChangjiangRiverandtheQiantangRiverprovidea1otoffreshwatertotheEastChinaSea.Somanywatersource%thecomplicatedoceantoPOgraphyasw…     

The calculation of Kuroshio current structure in the East China Sea—early summer 1986

On the basis of hydrographic data and moored current meter records obtained during an early summer cruise (May 20–June 23) of 1986, a three dimensional diagnostic calculation of the circulation is performed in the survey area, which covers the East China Sea continental shelf, Okinawa Trough and an area east of the Ryukyu Island. The Kuroshio Current condition and structure in the East China Sea, its branches and their interrelationship as well as the eddies around the Kuroshio, are discussed. When the Kuroshio entered the area northeast of Taiwan, there were two branches. The main branch flowed northeastward along the continental slope and the other branch was at the eastern part of the Okinawa Trough. The main axis of the Kuroshio followed the continental slope above the 300 m level, but moved gradually eastward to the Okinawa Trough below the 300 m level.     

Recent changes of the halocline characteristics and warming of the intermediate water in the Kamchatka current and the Oyashio

The upper Oyashio intermediate water, one of the source waters for the Sea of Okhotsk intermediate water, is exhibiting a warming trend. The historical data show that the upper Oyashio temperature increased by 2.4°C during 1953 to 2007 at the potential density of 26.75 at depths of approximately 170 m. This rate of warming is much faster than that of the global ocean and the Sea of Okhotsk. The upper Oyashio warming is likely linked to the penetration of warm water of the Alaskan Stream westward. One mechanism of this warm Alaskan Stream water penetration is associated with large Aleutian eddies.     

Study on short-range numerical forecasting of ocean current in the East China Sea——Ⅰ Basic problems of ocean current forecasting and structure of the models

Ocean current forecasting is still in explorative stage of study. In the study, we face some problems that have not been met before. The solving of these problems has become fundamental premise for realizing the ocean current forecasting. In the present paper are discussed in depth the physical essence for such basic problems as the predictability of ocean current, the predictable currents, the dynamical basis for studying respectively the tidal current and circulation, the necessity of boundary model, the models on regions with different scales and their link. The foundations and plans to solve the problems are demonstrated. Finally a set of operational numerical forecasting system for ocean current is proposed.     

东海黑潮强度与东亚冬季风关系的分析研究

利用卫星高度计资料和再分析资料,本文分析研究了东海黑潮强度与东亚冬季风的关系,并初步探讨了二者相互作用的可能机制。结果表明,位置相近的断面,其流强变化具有相似的特征;在年际尺度上,冬季风与东海黑潮存在相互作用。当冬季风偏强,将削弱次年2-4月SC、SD断面的流强,弱冬季风年的情况相反。冬季风对流强影响的动力过程主要通过改变Ekman输送来实现;热力过程则表现为强（弱）冬季风增大（减少）了黑潮向大气释放的热通量,从而削弱（增强）流强,这一过程主要为冬季风对黑潮的影响。当冬季风偏强时,次年10-12月黑潮中下游流强偏弱,弱冬季风年的情况相反。这一过程与2-4月情况不同,其热力过程主要表现为黑潮对冬季风的影响。强冬季风通过准两年振荡对次年冬季的黑潮流强产生影响,由此构成了一个包含海洋和大气耦合过程的正反馈机制。黑潮流域的海气相互作用过程可能受冬季风和黑潮流强相对强弱的调制,海洋过程和大气过程主导一方的转换中存在一个“临界值”。     

黑潮与东海水交换研究

利用高分辨率ROMS(regional ocean modeling system)数值模式模拟东海地区的多年平均流态。数值模拟结果在黑潮的流速、路径、流量等方面与近年来对黑潮的认识相一致。利用模式结果,计算东海及邻近海域主要水道的水通量。结果表明:台湾海峡、中国台湾-西表岛之间水道是海水进入东海的主要通道,对马海峡、吐噶喇海峡、大隅海峡与西表岛-宫古岛-冲绳岛-庵美大岛之间水道是海水流出东海的主要通道。分析PN断面的流量的变化特征,结果表明黑潮流量在春季与夏季较大,秋季与冬季较小,年平均流量为24.16 Sv,与前人研究结果一致。计算跨越200 m等深线的年平均净向岸体积输送为0.99 Sv,在台湾东北与九州西南地区表现为黑潮入侵陆架地区,年平均入侵流量分别为1.907 Sv与0.065 Sv,在黑潮中段地区,跨越200 m等深线流量呈现交错状分布,年平均净通量为0.982 Sv,表现为由东海陆架地区流向黑潮。上述结果对黑潮与东海之间物质与能量交换研究有一定参考价值。     

Horizontal structure of the temperature field of the upper layer in the northwest part of the Tropical Atlantic

By using the data of observations over the spatial variability of the temperature field in the northwest part of the Tropical Atlantic carried out in a test range 400 × 400 miles in size with a horizontal resolution Δx ≈ 2 km and a vertical resolution Δ_z ≈ 0.5 m, we recorded quasiperiodic fluctuations of temperature with semidiurnal period in the subsurface layer. The internal baroclinic waves with the same period generated, most likely, on the northeast shelf of South America and propagating to the northeast are detected in the seasonal thermocline. The vertical fine structure of the temperature field has different intensities in the test range. The maximum levels of dispersions of temperature fluctuations are recorded on the boundary of the North Equatorial Countercurrent and the North Equatorial Current. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 44–52, November–December, 2006.     

台风背景下海浪对海表流场和海表温度的影响

海浪作为海-气界面中重要的物理过程,对海洋上混合层的近表面分布具有重要作用。本文以台风"威马逊"和"麦德姆"为背景,基于FVCOM耦合模式模拟了台风浪及上层海洋的响应过程,探讨了海浪对海表流场和海表温度的影响。结果表明耦合模式能够较准确地模拟出有效波高,台风过境后海表流场在海浪的作用下反映出与台风相对应的气旋性特性,改变的流场量级可达0.4 m/s;海表温度出现不同程度的下降,最大降温约4℃,最大降温中心与流场变化区域相对应,且降温区相对台风路径呈显著的"右偏性"。最大降温滞后台风中心过境2 d左右,恢复时间一般超过10 d,与实况相吻合。     

东中国海潮流结构数值模拟与分析

采用FVCOM海洋数值模式建立了东中国海三维潮汐潮流的数值模型,并模拟了该海域的潮波运动。通过潮流的数值实验结果与实测结果的对比分析发现,半日分潮流的最大流速值随经度和纬度的增加逐渐减小,且极值点出现的深度呈递增趋势;最大流速的流向从低纬至高纬右旋,但随经度增大会发生左旋,流向极值点深度随纬度增大会逐步减小。低纬度海区的全日分潮流最大流速值高于高纬度海区;最大流速的流向的变化与半日分潮流相同,但流向极值点深度随经度增大会逐步增加。在垂向上,半日分潮流最大流速随深度的增加先增大后减小,最大流速的流向在流向极值点深度的上层右旋(顺时针),在下层左旋(逆时针);全日分潮流的最大流速在垂向上呈递减趋势,其流向同样是在流向极值点深度的上层右旋,在下层左旋。     

渤黄东海40年温盐流模拟与初步分析

使用ROMS(regional oceanic modeling system)模式模拟了40年的渤黄东海温盐流,数据包括三维的温度、盐度、流速、流向和海表高度,同时包含了逐小时的潮汐信息。将模拟结果与观测资料和卫星反演数据进行对比,检验了模式准确性。整体上,模式模拟的水位与近岸观测值基本一致,能够准确再现风产生的增水;模式较为准确的再现了渤黄东海的温度分布,在深水区模拟的温盐剖面与观测值基本一致;模式模拟渤黄东海区域的海表高度和海表流与卫星反演结果相比偏小,但分布趋势相近。模式结果可以为研究气候变化对水位的影响和黄海暖舌的扩散过程等现象提供数据支持。     

Meander of the Kuroshio front and current variability in the East China Sea

To investigate the fluctuation of the Kuroshio front, moored current meters were deployed near the shelf break and on the continental slope in the East China Sea, northwest of Okinawa Island, during a period from 25 June to 22 July 1984. Two mooring arrays were deployed on the slope of about 800 m water depth (under the Kuroshio), about 30 km apart along the path of the Kuroshio. Another two arrays were set near the shelf break of about 300 m water depth. The fluctuation of current on the slope is found to have a predominant period of 11–14 days and a were length of 300–350 km, propagating toward the downstream direction of the Kuroshio with a phase velocity of about 30 cm sec^?1. When the Kuroshio front approaches the shelf break and the crest of the meander covers the mooring site, the current direction moves toward the downstream direction of the Kuroshio and the water temperature increases. On the other hand, when the trough of the meander covers the mooring site, the current direction changes off-shoreward across the Kuroshio or in the upstream direction of the Kuroshio, and the water temperature decreases. Three-dimensional distributions of water temperature and salinity around the mooring site were observed with a CTD twice at 5.5 days intervals, which indicate the meanders of the front is about 180° out of phase. This coincides with a period of 11–14 days obtained with the moored current meters. Wave lengths of the dominant meander of the front in the satellite thermal images were about 350 km and 100–200 km, which also coincides with results obtained with the moored current meters.     

1991-2011年东海黑潮PN断面流结构与季节变化分析

基于日本海洋信息中心提供的东海黑潮PN断面CTD资料,本文采用动力高度法计算了1991-2011年间90个航次的断面流速,并对流场结构、最大流速、流幅和流量进行了统计分析。结果表明:东海黑潮PN断面流场存在单核、双核、多核3种结构;其中单核结构出现的概率为50%,双核结构为39%,多核结构为11%。东海黑潮的流结构存在显著的季节变化:秋季多核结构所占的比重为4个季节最大,平均流核数最多;冬季主要为单核结构,平均流核数最少;夏季和春季则没有明显的倾向性,单核、双核、多核3种结构出现概率相近,平均流核数介于秋季和冬季之间。其次东海黑潮的流量也存在显著的季节变化:冬季与夏季最强,秋季最小,春季居中。最后东海黑潮的最大流速和流幅也存在季节变化:夏季最大,秋季最小,春季和冬季居中。     

吕宋海峡海面涡度场与地转流场的特征分类

基于AVISO卫星高度计数据计算得到的地转流场,利用SOM神经网络对吕宋海峡海面涡度场与地转流场进行特征分析,研究吕宋海峡上层流场的变化特征。结果表明:在SOM 2×2的网络结构实验中,4个分类结果的空间形态类似于气候态的季节分布形式,其中冬季型可以由11月延续至次年3月,夏季型在5月至9月都会存在。时间序列显示分类结果存在年际变化信号,其中在ENSO较强的年份,季节变化信号明显。SOM 3×4网络结构的结果显示,12个分类结果可以分为4类,即冬季型、春季型、夏季型、秋季型。每种类型内的分类图形形态存在差别;在时间上,分类图形存在连续性,并集中出现在某个月份。时间序列显示季节变化信号与年际变化信号同时存在。     

A note on the horizontal momentum exchange in combined waves and current

The horizontal exchange of momentum due to the organized motion in combined waves and current has been analyzed. The combination of the vertical orbital wave motion and the mean current gives a periodic variation in the horizontal velocity in addition to the wave orbital motion. This periodic variation, combined with the wave orbital motion, gives a significant contribution to the momentum exchange. Two examples are considered, the interaction of a pure wave motion and a current normal to the direction of wave propagation, and a wave driven longshore current with an undertow velocity profile. It is demonstrated that the new contribution changes the resulting momentum exchange considerably.     

Numerical modelling of the tide-induced residual current in the East China Sea

-A two-dimensional.nonlinear numerical model is used to study the residual current generated by tides in the East China Sea (ECS)and the South Huanghai Sea (SHS). At first, the principal semidiurnal lunar tide (M2)and the tidal current are derived in these areas. The results obtained with the model are strongly supported by the observational results available. Then, the tide-induced residual flow is determined by using the currents generated by the tidal input. The main features of the residual current in ECS and SHS are presented by analyzing the calculated results. Some of the problems are discussed such as the cause of generating residual current and the contribution of the residual current to the observed current.     

Fine vertical structure of currents and hydrological elements in the Black Sea

Data on the fine vertical structure of currents and hydrological elements in the Black Sea, obtained through the use of a hydrophysical OLT profiler, are examined. Vertical exchange coefficients are evaluated, whose distribution is characterized by the occurrence of minima in the seasonal pycnocline and main halocline, a maximum in the core of the cold intermediate layer (CIL), and relatively steady values within the 300–500 m layer. The vertical exchange coefficient values, are consistent with the data acquired through other techniques, and the profiles of this parameter vertically are more detailed.Translated by Vladimir A. Puchkin.     

Water exchange in a time-varying transport field

The average residence time and the remnant function which are quantitative expressions of water exchange in coastal waters are investigated in a timevarying transport field by using a simple model. It is shown that the influence of temporal variation on the average residence time and concentration is small, when the ratio of the period of variation to the average residence time in the average state is small, and the influence is large when the ratio is large. The results are applied to the Seto Inland Sea, Lake Hamana, and Osaka Bay.