Hydrological analysis of Kuroshio water intrusion into the South China Sea

IN~crIONInvestigation of physical oceanography in the sleuth China Sea can be traced back tO the early17th century. America, England, Japan and Russia all carried out investigations in the sea. Butthe survey areas were limited and the data were scrappy. After entering this century big progresshas been achieved in the investigation of the sea both in the scale of survey and the depth ofstudy. So far the papers such as "Wind and drift currents in the mouth China Sea" (Dale, 1956)and "Phys…     

南海表层流场的卫星跟踪浮标观测结果分析

运用卫星跟踪漂移浮标资料分析南海表层海流 ,研究了有关海域的表层海流特征。结果表明 ,秋、冬季入侵南海的黑潮水有一小部分沿台湾南岸折回黑潮主干 ,并有时在台湾西南外海形成反气旋涡旋 ,其余大部分黑潮水西行进入南海内部。吕宋岛西部沿岸流始于 1 3°N以南 ,沿菲律宾西海岸北上抵达吕宋岛西北角 ,与黑潮水混合后西行     

Movement of the Kuroshio axis to the northeast shelf of Taiwan during typhoon events

We investigated the movement of the Kuroshio axis on the northeast shelf of Taiwan associated with the passage of typhoons, using sea surface current data observed by the ocean radar system on Yonaguni and Ishigaki islands. First, we examined daily Kuroshio axis variation on the northeast shelf of Taiwan during typhoon events. The ocean radar data showed that the Kuroshio axis moved onto the shelf after passages of typhoons. The Kuroshio moved onto the shelf and stayed there after the passage of Typhoon Hai-Tang; while the Kuroshio maintained this pattern, southerly wind blew continuously for 4 days. The mean current speed northeast of Taiwan after the typhoon's passage increased by 18 cm s⁻¹. In addition, the sea level difference between two satellite altimetry tracks east of Taiwan increased by 14.4 cm. These results suggest that coastal upwelling east of Taiwan caused by the southerly wind generated an east–west sea level difference that, in turn, generated a northward geostrophic current. This current could have enhanced the Kuroshio east of Taiwan, and pushed it onto the shelf.     

Source water of two-pronged northward flow in the southern Taiwan Strait in summer

It is generally accepted that the flow is northward in the Taiwan Strait during summer and that the strongest current is detected in the Penghu Channel between the Penghu Islands and the Taiwan Island. This current, the eastern prong flow, is made up of waters from the South China Sea (SCS) and the Kuroshio. North of the Penghu Islands, the current veers to the west before turning northward again because of the shallow Chang-Yuen Ridge, and extends westward off the coast of Taiwan. There is a second prong of northward flow existing between the Taiwan Bank and the China mainland coast. Here, we show with observational data as well as results from a numerical model that this water receives little influence from the Kuroshio and is distinctively cooler, fresher, less oxygenated and more acidic, and contains more dissolved inorganic carbon than waters at the same density level of the eastern prong. Evidence is provided to show that the source water of the western prong should be the subsurface water from the strong upslope advection flowing northward from the SCS to the southern Taiwan Strait and upwelling along the coast during the favorable southwesterly wind. Subsequently, the upwelled water flows over the saddle west of the Taiwan Bank and joins the main flow northwest of the Penghu Islands.     

黑潮水入侵南海的水文分析──Ⅱ.1994年8—9月期间的观测结果

利用1994年8－9月期间，由台湾海峡两岸的4艘海洋调查船在南海东北部海域所获之CTD和ADCP资料，并结合1992年3月间在同一海域获取的CTD资料及部分历史水文资料，对该区域的海水特性以及黑潮水入侵南海等问题进行了分析探讨。结果表明：调查期间，本海区水团分布与冬末、春初（1992年3月）航次基本相似，即南海和西北太平洋海域的海水结构有着各自相对独立的温、盐度特性。虽发现有黑潮水穿越巴上海峡进入南海，但其势力甚弱。因此，在夏末秋初，黑潮亦无直接的分支深入南海，即使在巴士海峡北端进入台湾海峡的黑潮水，其影响也是十分微弱的。由等密度面、地转流分析和实测ADCP资料显示，在调查海区的东南海域存在一支较强的N向流动。它沿菲律宾西海岸北上，绕过吕宋岛西北角流向东北，在巴上海峡呈现与黑潮水混合的迹象，其水体在冬季明显呈高温、低盐的特性；夏季则为相对低温、低盐。故在冬季的几幅卫星图像上也有较好的体现，很有可能长年存在。     

Surface current field and seasonal variability in the Kuroshio and adjacent regions derived from satellite-tracked drifter data

The muhiyear averaged surface current field and seasonal variability in the Kuroshio and adjacent regions are studied. The data used are trajectories and （1/4） ° latitude by （1/4） ° longitude mean currents derived from 323 Argos drifters deployed by Chinese institutions and world ocean circulation experiment from 1979 to 2003. The results show that the Kuroshio surface path adapts well to the western boundary topography and exhibits six great turnings. The branching occurs frequently near anticyclonic turnings rather than near cyclonic ones. In the Luzon Strait, the surface water intrusion into the South China Sea occurs only in fall and winter. The Kuroshio surface path east of Taiwan, China appears nearly as straight lines in summer, fall, and winter, when anticyclonic eddies coexist on its right side; while the path may cyclonically turning in spring when no eddy exists. The Kuroshio intrusion northeast of Taiwan often occurs in fall and winter, but not in summer. The running direction, width and velocity of the middle segment of the Kuroshio surface currents in the East China Sea vary seasonally. The northward intrusion of the Kuroshio surface water southwest of Kyushu occurs in spring and fall, but not in summer. The northmost position of the Kuroshio surface path southwest of Kyushu occurs in fall, but never goes beyond 31 °N. The northward surface current east of the Ryukyu Islands exists only along Okinawa-Amami Islands from spring to fall. In particular, it appears as an arm of an anti- cyclonic eddy in fall.     

A high-resolution numerical modeling study of the subtidal circulation in the northern South China Sea

A high-resolution, regional, numerical-model-based, real-time ocean prediction system for the northern South China Sea, called the Northern South China Sea Nowcast/Forecast System (NSCSNFS), has been used to investigate subtidal mesoscale flows during the time period of the Asian Seas International Acoustic Experiment (ASIAEX) field programs. The dynamics are dominated by three influences; 1) surface wind stress, 2) intrusions of the Kuroshio through Luzon Strait, and 3) the large-scale cyclonic gyre that occupies much of the northern South China Sea. Each component primarily drives currents in the upper ocean, so deep currents are rather weak. Wind stress is especially effective at forcing currents over the shallow China shelf. The Kuroshio intrusion tends to flow westward until it meets the northern edge of the large-scale cyclonic gyre. Together, these currents produce an intense, narrow jet directed northwest toward the continental slope, often in the region of the ASIAEX field programs. Upon reaching the slope, the current splits with part flowing northeastward along the slope and part flowing southwestward, producing large horizontal and vertical shears and making this region dynamically very complicated and difficult to simulate. The Kuroshio intrusion tends to be stronger (weaker) when the northeasterly winds are strong (weak) and the large-scale gyre is farther south (north), consistent with conclusions from previous model studies. At the northern boundary, the model produces a persistent northward flow through Taiwan Strait into the East China Sea. Data assimilation in the NSCSNFS model is shown to dampen the system, extracting energy and causing the entire system to spin down.     

黑潮跨陆架入侵东海年际变化的数值模拟

为了研究黑潮跨过200m等深线对东海入侵的年际变化特征,本文基于ROMS(Regional Ocean Modeling System)海洋模式,对西北太平洋海域进行了高分辨率的数值模拟,模式水平分辨率高达4km,该分辨率可以很好地分辨黑潮以东区域的中尺度涡旋等过程。模式首先进行了6年的气候态模拟,然后进行了1993到2015年的后报模拟。模式很好地再现了东海陆架已知的环流结构,模拟出的对马海峡和台湾海峡的年平均流量和观测结果也比较一致。基于模式结果,利用旋转经验正交函数(REOF)的方法,对黑潮跨过200m等深线流量的年际变化进行分析。REOF的主要模态表明,黑潮跨过200m等深线对东海陆架的入侵主要发生台湾东北,并且入侵主要集中在黑潮次表层水中。主要模态的时间系数表明,黑潮入侵东海陆架的年平均流量存在一个8年的变化周期。相关性分析表明,黑潮入侵东海陆架的年际变化和太平洋年代际振荡PDO(Pacific Decadal Oscillation)指标具有显著的负相关,其相关系数达–0.63。该相关可以通过如下过程解释:PDO会导致东太平洋风应力涡度异常,由Sverdrup关系可知向赤道的体积输运也会相应地产生异常,根据质量守恒,向赤道体积输运的异常必然通过西边界流-黑潮的异常来平衡,从而导致黑潮入侵东海陆架强烈的年际变化。     

黑潮与邻近东海生源要素的交换及其生态环境效应

黑潮与东海生源要素的交换对东海的生态环境有重大影响,交换主要是经台湾东北部海域输送至东海陆架和通过日本九州西南海域由东海陆架向外海的黑潮输出两个通道。中国科学院海洋先导专项对黑潮与邻近东海生源要素的交换特征进行了系统的调查和研究,获得了一些新的认识:(1)在台湾东北部区域,碳主要以表层水-次表层水为载体输入,秋季的输入量高于夏季;黑潮溶解态营养盐的输入占据绝对主导地位,且以黑潮次表层热带水-中层水的输入为主,输入通量春季高于夏、秋季,可为东海春季水华提供一定的物质基础,但输入到东海的黑潮水其氮磷比与Redfield比值(16:1)接近,这些"正常水"——黑潮的输入显然对调和东海异常高的氮磷比有重要的作用,从而对东海的生态环境起到"稳定和缓冲"作用。所以,黑潮水对东海的输入不仅维持补充了东海生态系统运转所需的生源要素,更为重要的是缓冲了受人为影响强烈的东海海水的高氮磷比,使东海本已失常的营养盐结构向合适的氮磷比方向转变。因此,黑潮与东海生源要素的输入在一定程度上起着稳定和缓和东海生态环境的作用。(2)通过构建的海水Ba-盐度新指标体系,定量细致刻画了黑潮对东海生源物质在台湾东北部区域的输入范围和程度,黑潮次表层水从台湾东北陆架坡折处沿底部向北偏西方向入侵东海,其近岸分支可以入侵到浙江近岸,其黑潮次表层水占比仍可达到65%左右。垂直方向上,陆架外侧站位受黑潮次表层水的影响范围更大,黑潮水占50%比例位置可延伸至外侧TW0-1站位(122.59°E,25.49°N)表层,而内侧靠近大陆的站位则只限于陆架中部位置底层。     

Effect of Taiwan Strait Current on the onshore intrusion of Kuroshio: A geostrophic adjustment model

The effect of the Taiwan Strait Current on the onshore intrusion of Kuroshio, both contributing to the formation of Tsushima Warm Current, is addressed theoretically by invoking a geostrophic adjustment model previously proposed. The idealized model assumes two unbounded basins, shallow and deep, separated by an infinitely long and thin barrier. On either side of the barrier, a western boundary current in the deep basin and a shelf current in the shallow basin flow along the barrier with the surface elevation of the former higher than that of the latter. When a part of the barrier is removed and a gap is created, the onshore part of the western boundary current intrudes onto the shallow basin through the gap while conserving its potential vorticity. Both the intruding current and the shelf current will later geostrophically adjust themselves to the disturbances created by the intrusion. Model results show that the transport of onshore intrusion increases with the sea level difference imposed initially between the deep and shallow basins across the barrier, indicating that the sea level rise associated with the strengthening of shelf current inhibits the shelf-ward intrusion. The intruding current is in jet mode when its transport is maximized, which otherwise is in coastal mode. The maximization of transport occurs when the sea level difference between the two basins is sufficiently large. Although this model greatly idealizes the problem, it explains well the observed fact that the transport of Tsushima Warm Current is fed mostly by the Taiwan Strait Current in summer when the latter becomes the strongest, and by the onshore intrusion of Kuroshio in winter when the Taiwan Strait Current nearly vanishes, suggesting that the seasonal variation of the onshore intrusion of Kuroshio is largely due to the seasonal variation in the strength of the Taiwan Strait Current.     

利用被动示踪物模拟对黑潮入侵南海的数值研究

由于缺少观测数据和对黑潮水准确定义,很难识别出从太平洋入侵到南海的黑潮水团。本文基于一个经过观测验证的三维模式MITgcm,利用被动示踪物标记黑潮水,研究了入侵南海的黑潮水的时空变化。研究表明,在冬季,黑潮水入侵的范围最广,几乎占据了18°N-23°N和114°E-121°E的区域;并有一个分支进入台湾海峡;黑潮入侵的范围随深度增加逐渐减小。在夏季,黑潮水被限制在118°E以东,且没有分支进入台湾海峡;入侵的范围从海面到约205米是增大的,之后随深度增加逐渐减小。通过分析从2003年到2012年黑潮入侵的年际变化,与厄尔尼诺年和正常年相比,冬季黑潮入侵后向台湾海峡的分支在拉尼娜年是最弱的,这可能与中国大陆东南方向的风应力旋度有关。通过吕宋海峡的黑潮入侵通量（KIT）是西向的,其年平均值约为-3.86×10⁶ m³/s,大于吕宋海峡通量（LST,约-3.15×10⁶ m³/s）。250米以上的KIT约占了全深度通量的60-80%。此外,从2003年到2012年KIT与Niño 3.4指数的相关系数到达0.41,小于LST与Niño 3.4指数的相关系数0.78。     

黑潮近岸分支流在2017年9月与2019年9月差异的研究

通过对比2017年9月和2019年9月的温盐大面观测数据,发现东海陆架上黑潮近岸分支流的路径在两次观测中存在显著差异。2019年9月黑潮近岸分支流中上游的路径相较2017年9月明显的东向偏移,造成黑潮次表层水入侵东海近岸海域的强度较弱。为了探究黑潮近岸分支流的上述显著年际差异的原因,利用卫星高度计数据和再分析风场数据,通过分析大面观测同期的绝对海表动力高度、地转流场以及海表风场的差异,阐述了黑潮近岸分支流路径产生显著年际差异的动力机制。2019年8—9月东海海表较2017年8—9月盛行更强的西南向沿岸季风,强的西南向沿岸风通过埃克曼输运促使水体向岸堆积并在近岸区域沿岸西南向堆积。因此, 2019年8—9月东海近岸海域的跨岸方向压力梯度与2017年8—9月相比较小而沿岸压力梯度则较大。2019年8—9月,受压力梯度分布的影响,东海近岸海域产生西南向的沿岸地转流和离岸地转流。其中西南向的沿岸地转流会在底部生成离岸的底埃克曼流,离岸底埃克曼流和离岸地转流共同抑制了黑潮近岸分支流的向岸入侵。这导致2019年9月黑潮近岸分支流的路径向东偏移,黑潮次表层水入侵浙江近海及长江口区域的强度随之减弱。通过分析研究实际观测案例,阐述了风影响黑潮近岸分支流入侵东海近岸海域的动力机制,同时明确指出海表风场会从黑潮近岸分支流的中上游区域改变其路径,进而对黑潮入侵东海近岸海域产生重要影响。     

西北太平洋黑潮源区沉积特征及黑潮输入对东海沉积物的影响

在对海流和地质背景分析的基础上将源区黑潮划分为3个区域,即北赤道流区、吕宋岛以东海区和台湾东部黑潮主干区,归纳总结了其沉积物矿物组成、元素组分特征和物源研究结论,探讨了黑潮输入对东海沉积物的影响。总体看来,黑潮源区沉积物的主要外来源是菲律宾群岛、菲律宾岛弧、台湾河流输入和亚洲大陆风尘的输入。黑潮源区沉积物矿物分布受菲律宾海沟的阻隔、北赤道流与黑潮的营力作用、海底火山热液活动和水深影响较大,常量元素组成主要与海底地形和水深有关,稀土元素组成表现出具有明显陆源输入的边缘海沉积特征,Sr、Nd同位素组成的研究在该区主要用于追踪亚洲风尘输入。由于黑潮入侵东海多分支的复杂性,东海黑潮对陆架沉积物的影响尚需深入研究。进一步研究应在台湾东部沉积物物源分析、黑潮输入对东海沉积物影响的历史变化、多指标整合的综合分析方法、有效物源识别端元的构建等方面展开。深入研究黑潮源区沉积特征及物源可有效揭示黑潮流域变化、构造活动和气候变化等,且探明黑潮输入对东海陆架沉积物分布的影响有利于揭示东海生态环境变化和海洋资源环境的可持续利用。     

风对中国东部海域海平面季节变化的影响

应用ROMS数值模式配置基本实验模拟了2004年到2006年中国东部海域海平面的季节变化。模拟结果与TOPEX／Poseidon（T／P）卫星高度计观测结果基本一致,海平面年较差从中国沿岸到黑潮路径逐渐变小。将数值模式的风应力项去掉,配置对比实验。与基本实验结果对比发现,对比实验海平面仍然具有季节变化,但是闽浙沿岸和苏北沿岸海平面春夏季异常偏低、秋冬季异常偏高现象消失,中国沿岸向太平洋的海平面变化减弱。春季和秋季,渤、黄海和黑潮附近海平面异于东海的现象减弱。对比实验海平面的年较差的数值明显减小,从近岸向黑潮海平面年较差渐变的过程消失。整个渤黄海的海平面年较差近似。对比实验海平面年较差占基本实验海平面年较差比率从近岸向黑潮路径逐渐增大。     

Numerical Study of the Upper-Layer Circulation in the South China Sea

Upper-layer circulation in the South China Sea has been investigated using a three-dimensional primitive equation eddy-resolving model. The model domain covers the region from 99° to 122°E and from 3° to 23°N. The model is forced by the monthly averaged European Centre for Medium-Range Weather Forecasts (ECMWF) model winds and the climatological monthly sea surface temperature data from National Oceanographic Data Center (NODC). Inflow and outflow through the Taiwan Strait and the Sunda shelf are prescribed monthly from the Wyrtki estimates. Inflow of the Kuroshio branch current in the Luzon Strait is assumed to have a constant volume transport of 12 Sv (1 Sv = 10⁶ m³/s), and the outflow from the open boundary to the east of Taiwan is adjusted to ensure the net volume transport through all open boundaries is zero at any instant. The model reveals that a cyclonic circulation exists all year round in the northern South China Sea. During the winter time this cyclonic eddy is located off the northwest of Luzon, coinciding with the region of positive wind stress curl in this season. This cyclonic eddy moves northward in spring due to the weakening of the northeast winds. The cyclonic circulation becomes weak and stays in the continental slope region in the northern South China Sea in the summer period. The southwest wind can raise the water level along the west coast of Luzon, but there is no anticyclonic circulation in the northern South China Sea. After the onset of the northeast monsoon winds in fall, the cyclonic eddy moves back to the region off the west coast of Luzon. In the southern South China Sea and off the Vietnam coast, the model predicts a similar flow structure as in the previous related studies. This revised version was published online in July 2006 with corrections to the Cover Date.     

孟加拉湾上层环流研究综述

综述了孟加拉湾上层环流研究的主要成果并指出,研究海区环流与季风转换不完全同步。在西南季风期间,南、北海区各有一气旋式环流;在秋季季风过渡期间,出现海湾尺度的气旋式环流;在东北季风期间,气旋式环流减弱北移,南部则为一反气旋式环流控制;春季与秋季的情形相反,整个湾出现一海湾尺度的反气旋式环流。研究海区环流的变异主要受季风、赤道远地作用和浮力通量等复杂外源作用的影响。东印度沿岸流的季节变化与季风转换也不同步,局地风、内部Ekman抽吸、远地沿岸风及赤道远地作用的影响对沿岸流周年变化有重要作用。孟加拉湾上层环流年际变化显著,此年际变化主要受赤道风场的影响。     

Argos漂流浮标的若干观测结果

表层漂流浮标是一种利用Argos卫星系统定位与传送数据的海洋观测设备,它可以利用Lagrangian法则连续观测表层海流及表层水温。文章利用近年在南海和西太平洋投放的部分卫星跟踪表层漂流浮标所取得的观测资料,分析观测海域的表层海流特征及其漂移路径上的温度变化,得出以下结果。(1)由浮标的漂移轨迹看出,黑潮表层流路年际变异相当大。(2)2003年1月,黑潮表层水有入侵南海的趋势,似无西北太平洋表层水深入南海的迹象;夏季南海表层水由南海流出经吕宋海峡汇入黑潮主干。(3)秋季台湾东北海区存在一个强反气旋涡,空间尺度约270km。(4)黑潮主干在秋末冬初经过东海时明显呈弯曲流动,并形成许多小尺度的气旋式涡。(5)在九州西南海域,黑潮表层流并无分支北上进入对马暖流区。(6)2003年春季,黑潮在日本以南的弯曲不明显,并伴随有冷、暖涡产生,暖涡的强度和空间尺度都要比冷涡大得多。(7)由漂流浮标观测得到的的表层海水的温度分布明显呈日变化和季节变化的特征。在浮标漂移路径呈反气旋或气旋式转动的区域,表层水温对应出现高或低温区;但出现在台湾以东的低温区则与此时期的台风过境有关。     

2006年夏季琼东、粤西沿岸上升流研究

利用2006年夏季广东、海南、广西近海的海洋水文调查资料和卫星遥感QuikSCAT风场资料分析琼东、粤西沿岸上升流的空间结构特征, 探讨风场、风应力旋度对上升流的影响以及上升流区水温、海流、海平面对上升流的响应。结果表明:琼东、粤西沿岸上升流区并非相互独立, 从10 m层以下已经连成一片。琼东沿岸上升流主要由夏季西南季风驱动而产生, 风应力旋度也有一定贡献。琼东沿岸上升流的强度比粤西强。琼东沿岸海域的上层海水(18 m以浅)以离岸运动为主, 中下层海水以向岸运动为主。上层的离岸流速大于中下层的向岸流速。琼东沿岸的上升流现象是间歇性的, 与沿岸风速强弱有关。琼东沿岸海域海平面的升降与上升流的强弱有良好的关系, 上升流的强弱滞后于海平面的升降约1～2 d。     

基于海色融合数据的东海黑潮锋面检测研究

海洋锋是典型的海洋中尺度现象之一。目前卫星遥感主要利用海表温度数据分析海洋锋,但由于西北太平洋海域夏季海表温度的趋同特性,不能进行有效的锋面监测;而不同水团所具有的生物光学特性往往是不同的,且不具有太阳辐射引起的显著性季节变化,因此海色资料也成为检测海洋锋的有效数据源。文中以东海黑潮为例,详细说明了基于叶绿素a浓度融合数据,采用梯度法进行海洋锋面检测的过程,通过比较不同季节不同梯度阈值得到的东海黑潮锋结果,从保持锋面的完整性及对零碎锋区的剔除效应方面,选取了不同季节较优的梯度阈值。总体来说,文中检测出的东海黑潮区域海色锋与海流黑潮强流区较吻合,12月至4月东海黑潮海色锋检测结果不如海温锋,而5-11月东海黑潮海色锋检测结果优于海温锋,特别是台湾以东黑潮区域,不论什么季节海温锋都没有体现,而海色锋始终很明显。利用文中提出的海洋锋检测算法、分析方法及选择的梯度阈值可以有效地检测东海黑潮区域的海洋锋面,结合海色锋和海温锋,可以监测分析东海黑潮强流区的时空变化。     

基于卫星高度计资料的黑潮入侵南海流径的时间变化规律研究

黑潮入侵南海对南海的温盐平衡、环流、涡旋和局地气候等具有重要作用。基于吕宋海峡处黑潮不同流径的识别方法,对1993～2021年的卫星高度计资料进行识别,获取黑潮不同流径的发生时间,探究黑潮入侵南海流径的时间变化规律。结果表明:(1)黑潮主要以流套(Looping)和分支(Leaking)两种流径入侵南海,Leaking流径发生的时长(710周)和概率(46.9%)要远高于Looping流径(时长218周,概率14.4%)。(2) Looping流径和Leaking流径均可将高温高盐的西北太平洋水带入南海,Looping流径下的平均吕宋海峡上层通量(6.3×10⁶ m³/s)略大于Leaking流径(5.6×10⁶ m³/s)Looping和Leaking流径在4×10⁶ m³/s～6×10⁶ m³/s区间发生时间最长。(3)季节变化上,Looping流径主要发生在冬季,Leaking流径在冬半年均较强,夏季二者发...