Formation of an anticyclonic eddy and the mechanism involved: a case study using cruise data from the northern South China Sea

Data from satellite altimetry and in situ observations together with the Hybrid Coordinate Ocean Model (HYCOM) reanalysis data were used to investigate the mechanism and formation of an anticyclonic eddy in the northeastern South China Sea (SCS). Analysis of water mass using cruise data indicated that the water captured in the eddy diff ers from those in the SCS, the Kuroshio intrusion, and the eddy-forming region. Data from sea surface height (SSH) and sea level anomaly (SLA) indicate that the eddy formed due both to the Kuroshio intrusion and the local circulation in the SCS. The Kuroshio intrusion is present at the start of the eddy growth (March 5-9) before Kuroshio leaps the Luzon Strait. The eddy then becomes larger and stronger in the absence of the Kuroshio intrusion. From the eddy budget of the HYCOM reanalysis data, the formation of the eddy goes in three steps. By the third step, the eddy had become aff ected by variations of local SCS circulation, which is more strongly than in the fi rst step in which it is aff ected more by the Kuroshio intrusion. The variability of the temperature and salinity inside the eddy provide a support to this conclusion. The water in the SCS intruded into the eddy from the southeast, which decrease the salinity gradually in the southern part of the eddy during the growth period.     

近岸波浪和波生流环境中泥沙输运的数值模拟

Owing to lack of observational data and accurate definition,it is difficult to distinguish the Kuroshio intrusion water from the Pacific Ocean into the South China Sea(SCS).By using a passive tracer to identify the Kuroshio water based on an observation-validated three-dimensional numerical model MITgcm,the spatio-temporal variation of the Kuroshio intrusion water into the SCS has been investigated.Our result shows the Kuroshio intrusion is of distinct seasonal variation in both horizontal and vertical directions.In winter,the intruding Kuroshio water reaches the farthest,almost occupying the area from 18°N to 23°N and 114°E to 121°E,with a small branch flowing towards the Taiwan Strait.The intrusion region of the Kuroshio water decreases with depth gradually.However,in summer,the Kuroshio water is confined to the east of 118°E without any branch reaching the Taiwan Strait;meanwhile the intrusion region of the Kuroshio water increases from the surface to the depth about 205 m,then it decreases with depth.The estimated annual mean of Kuroshio Intrusion Transport(KIT) via the Luzon Strait is westward to the SCS in an amount of –3.86×106 m3/s,which is larger than the annual mean of Luzon Strait Transport(LST) of –3.15×106 m3/s.The KIT above 250 m accounts for 60%–80% of the LST throughout the entire water column.By analyzing interannual variation of the Kuroshio intrusion from the year 2003 to 2012,we find that the Kuroshio branch flowing into the Taiwan Strait is the weaker in winter of La Ni?a years than those in El Ni?o and normal years,which may be attributed to the wind stress curl off the southeast China then.Furthermore,the KIT correlates the Ni?o 3.4 index from 2003 to 2012 with a correlation coefficient of 0.41,which is lower than that of the LST with the Ni?o 3.4 index,i.e.,0.78.     

Role of Kuroshio frontal eddy in exchange between shelf water and Kuroshio water in East China Sea

Basic patterns of the reversal of the Kuroshio water toward the shelf, intrusion of the shelf mixed waterinto the Kuroshio and uplifting of the near-bottom nutrient-rich water into the upper layer by the pumping of the frontal eddy are analyzed on the basis of satellite infrared images and hydrologic, chemical and biological observations. Results show that the Kuroshio frontal eddies play a very important role in the exchange between the shelf water and the Kuroshio water. The estimation of the average volume transports for three frontal eddy events indicates that the shelf mixed water entrained by an eddy into Kuroshio is 0.44×10~6 m3/s and the reversal Kuroshio water onto the shelf region only 0.04×10~6 m3/s. Along the whole shelf edge, the volume transport of the shelf mixed water entrained by the eddies into the Kuroshio is 1.8×10~6 m3/s. The nutrient (NO3-N) flux pumped to the euphotic zone and input to the continental shelf through a column with 1 m wide is 974 μmol/(s·m) when there is frontal eddy and only 79 μmol/(s·m) in the case of no frontal eddy. Yearly nutrient (NO3-N) flux input to the shelf area caused by the frontal eddy is 1.7×10~5 t/a.     

南海冬季之西边界流：1998年2月的水文结构与体积输运

The unique survey in December 1998 mapped the entire western boundary area of the South China Sea(SCS),which reveals the three-dimensional structure and huge volume transport of the swift and narrow winter western boundary current of the SCS(SCSwwbc) in full scale. The current is found to flow all the way from the shelf edge off Hong Kong to the Sunda Shelf with a width around 100 km and a vertical scale of about 400 m. It appears to be the strongest off the Indo-China Peninsula, where its volume transport reached over 20×10~6 m~3/s. The current is weaker upstream in the northern SCS to the west of Hong Kong. A Kuroshio loop or detached eddy intruded through the Luzon Strait is observed farther east where the SCSwwbc no more exists. The results suggest that during the survey the SCSwwbc was fed primarily by the interior recirculation of the SCS rather than by the"branching" of the Kuroshio from the Luzon Strait as indicated by surface drifters, which is likely a near-surface phenomenon and only contributes a minor part to the total transport of the SCSwwbc. Several topics related to the SCSwwbc are also discussed.     

Case study on the three-dimensional structure of meso-scale eddy in the South China Sea based on a high-resolution model

Meso-scale eddies are important features in the South China Sea(SCS). The eddies with diameters of 50–200 km can greatly impact the transport of heat, momentum, and tracers. A high-resolution wave-tide-circulation coupled model was developed to simulate the meso-scale eddy in the SCS in this study. The aim of this study is to examine the model ability to simulate the meso-scale eddy in the SCS without data assimilations The simulated Sea Surface Height(SSH) anomalies agree with the observed the AVISO SSH anomalies well. The simulated subsurface temperature profiles agree with the CTD observation data from the ROSE(Responses of Marine Hazards to climate change in the Western Pacific) project. The simulated upper-ocean currents also agree with the main circulation based on observations. A warm eddy is identified in winter in the northern SCS. The position and domain of the simulated eddy are confirmed by the observed sea surface height data from the AVISO. The result shows that the model has the ability to simulate the meso-scale eddy in the SCS without data assimilation.The three-dimensional structure of the meso-scale eddy in the SCS is analyzed using the model result. It is found that the eddy center is tilted vertically, which agrees with the observation. It is also found that the velocity center of the eddy does not coincide with the temperature center of the eddy. The result shows that the model has the ability to simulate the meso-scale eddy in the SCS without data assimilations. Further study on the forming mechanism and the three-dimensional structure of the meso-scale eddies will be carried out using the model result and cruise observation data in the near future.     

Kuroshio intrusion into the South China Sea with an anticyclonic eddy: evidence from underwater glider observation

In this study, high-resolution temperature and salinity data obtained from three Sea-Wing underwater gliders were used together with satellite altimeter data to track the vertical thermohaline structure of an anticyclonic eddy that originated from the loop current of the Kuroshio southwest of Taiwan, China. One of the gliders crossed the entire eddy and it observed a remarkable warm anomaly of as much as 3.9℃ extending to 500 dbar from the base of the mixed layer. Conversely, a positive salinity anomaly was found to be above 200 dbar only in the anticyclonic eddy, with a maximum value of >0.5 in the mixed layer. Below the mixed layer, water of higher salinity (>34.7) was found, which could have been preserved through constrained vertical mixing within the anticyclonic eddy. The salinity in the upper layer of the anticyclonic eddy was much similar to that of the northwestern Pacific Ocean than the northern South China Sea, reflecting Kuroshio intrusion with anticyclonic eddy shedding from the loop current.     

Submesoscale eddies in the East China Sea detected from SAR images

Seven-year(2005–2011) Synthetic Aperture Radar(SAR) images are applied to study oceanic eddies in the East China Sea. It is found that most of these eddies detected from the SAR images are less than 10 km, which are submesoscale eddies. Seasonal differences are evident in the distribution of eddies, with the highest and the lowest number of eddies noted in summer and winter, respectively. Since slick streaks in SAR images look dark, an eddy identified due to the slicks is referred to as "black eddy". As a result of wave-current interactions in the zones of current shear, it can be seen that an eddy exhibits a bright curve, the eddy is called "white eddy". During the seven years, 95 black eddies and 50 white eddies are identified in the study area. Black eddies are found in the whole study area while white eddies are mainly distributed in the vicinity of the Kuroshio Current. This study suggests that the distribution of the white eddy is denser around the Kuroshio because of the strong shear in the Kuroshio region. In terms of the eddy sizes, white eddies are generally smaller than black eddies.     

南海浅层经向翻转环流及相关的内部水体流动

The structure of the annual-mean shallow meridional overturning circulation(SMOC) in the South China Sea(SCS) and the related water movement are investigated,using simple ocean data assimilation(SODA) outputs.The distinct clockwise SMOC is present above 400 m in the SCS on the climatologically annual-mean scale,which consists of downwelling in the northern SCS,a southward subsurface branch supplying upwelling at around 10°N and a northward surface flow,with a strength of about 1×10~6 m~3/s.The formation mechanisms of its branches are studied separately.The zonal component of the annual-mean wind stress is predominantly westward and causes northward Ekman transport above 50 m.The annual-mean Ekman transport across 18°N is about 1.2×10~6 m~3/s.An annual-mean subduction rate is calculated by estimating the net volume flux entering the thermocline from the mixed layer in a Lagrangian framework.An annual subduction rate of about 0.66×10~6m~3/s is obtained between 17° and 20°N,of which 87% is due to vertical pumping and 13% is due to lateral induction.The subduction rate implies that the subdution contributes significantly to the downwelling branch.The pathways of traced parcels released at the base of the February mixed layer show that after subduction water moves southward to as far as 11°N within the western boundary current before returning northward.The velocity field at the base of mixed layer and a meridional velocity section in winter also confirm that the southward flow in the subsurface layer is mainly by strong western boundary currents.Significant upwelling mainly occurs off the Vietnam coast in the southern SCS.An upper bound for the annual-mean net upwelling rate between 10° and 15°N is 0.7×10~6m~3/s,of which a large portion is contributed by summer upwelling,with both the alongshore component of the southwest wind and its offshore increase causing great upwelling.     

Seasonal characteristics and forcing mechanisms of the surface Kuroshio branch intrusion into the South China Sea

Using observational data of Argos satellite-tracked drifters from 1988 to 2012, we analyzed seasonal characteristics of the surface Kuroshio branch(KB) intrusion into the South China Sea(SCS). The analysis results are as follows.The surface KB originates from the southern Balintang Channel(BLTC) and Babuyan Channel(BBYC). It begins in late September, reaches peak strength in November–December, and declines at the end of March. The mean speed of drifters along the KB path during their traverse of the Luzon Strait(LS) was 43% faster than during the two days before entering the LS for the flow originating from the southern BLTC, but there was a 24% increase in speed for the flow from the BBYC. The observations show that in winter, monthly-mean sea-level anomalies(SLAs) were positive southwest of Taiwan Island and extended to the northern LS. The SLAs were negative northwest of Luzon Island and extended to the southern LS, which acted like a pump, forcing a part of Kuroshio water westward into the SCS. The condition under which the KB forms was solved by a set of simplified motion equations. The results indicate that whether the KB can form depends upon the sea-level gradient at the central LS and region to the west, as well as the location, speed and direction of Kuroshio surface water when it enters the LS.     

中尺度涡影响下的南海西部活性铝分布

To understand the distribution of aluminum(Al) under the influence of mesocale eddies in the western South China Sea(SCS), sea level anomaly, geostrophic current, environmental parameters and reactive Al were investigated in the western SCS in August 2013. The highest reactive Al concentration((180±64) nmol/L) was observed in the surface waters, indicating a substantial atmospheric input. Vertically, the reactive Al decreased from the surface high concentration to the subsurface minima at the depth of chlorophyll a(Chl a) maxima and then increased again with depth at most of the stations. The average concentration of reactive Al in the upper 100 m water column was significantly lower in the cyclonic eddy((137±6) nmol/L) as compared with that in the noneddy waters((180±21) nmol/L). By contrast, the average concentrations of Chl a and silicate in the upper 100 m water column were higher in the cyclonic eddy and lower in the anticyclonic eddy. There was a significant negative correlation between the average concentrations of reactive Al and Chl a in the upper 100 m water column. The vertical distribution of reactive Al and the negative correlation between reactive Al and Chl a both suggest that the reactive Al in the upper water column was significantly influenced by biological removal processes. Our results indicate that mesoscale eddies could regulate the distribution of reactive Al by influencing the primary production and phytoplankton community structure in the western SCS.     

Effects of cold eddy on phytoplankton production and assemblages in Luzon strait bordering the South China Sea

The biochemical effects of a cold-core eddy that was shed from the Kuroshio Current at the Luzon Strait bordering the South China Sea (SCS) were studied in late spring, a relatively unproductive season in the SCS. The extent of the eddy was determined by time-series images of SeaWiFS ocean color, AVHRR sea surface temperature, and TOPEX/Jason-1 sea surface height anomaly. Nutrient budgets, nitrate-based new production, primary production, and phytoplankton assemblages were compared between the eddy and its surrounding Kuroshio and SCS waters. The enhanced productivity in the eddy was comparable to wintertime productivity in the SCS basin, which is supported by upwelled subsurface nitrate under the prevailing Northeastern Monsoon. There were more Synechococcus, pico-eucaryotes, and diatoms, but less Trichodesmium in the surface water inside the eddy than outside. Prochlorococcus and Richelia intracellularis showed no spatial differences. Water column-integrated primary production (IPP) inside the eddy was 2–3 times that outside the eddy in the SCS (1.09 vs. 0.59 g C m⁻²d⁻¹), as was nitrate-based new production (INP) (0.67 vs. 0.25 g C m⁻²d⁻¹). INP in the eddy was 6 times that in the Kuroshio (0.12 g C m⁻²d⁻¹). IPP and INP in the eddy were higher than the maximum production values ever measured in the SCS basin. Surface chlorophyll a concentration (0.40 mg m⁻³) in the eddy equaled the maximum concentration registered for the SCS basin and was higher than the wintertime average (0.29 ± 0.04 mg m⁻³). INP was 3.5 times as great and IPP was doubled in the eddy compared to the wintertime SCS basin. As cold core eddies form intermittently all year round as the Kuroshio invades the SCS, their effects on phytoplankton productivity and assemblages are likely to have important influences on the biogeochemical cycle of the region.     

Seasonal variation of eddy shedding from the Kuroshio intrusion in the Luzon Strait

Altimeter data and output from the HYbrid Coordinate Ocean Model global assimilation run are used to study the seasonal variation of eddy shedding from the Kuroshio intrusion in the Luzon Strait. The results suggest that most eddy shedding events occur from December through March, and no eddy shedding event occurs in June, September, or October. About a month before eddy shedding, the Kuroshio intrusion extends into the South China Sea and a closed anticyclonic eddy appears inside the Kuroshio loop which then detaches from the Kuroshio intrusion. Anticyclonic eddies detached from December through February move westward at a speed of about 0.1 m s⁻¹ after shedding, whereas eddies detached in other months either stay at the place of origin or move westward at a very slow speed (less than 0.06 m s⁻¹). The HYCOM outputs and QuikSCAT wind data clearly show that the seasonal variation of eddy shedding is influenced by the monsoon winds. A comparison between eddy volume and integrated Ekman transport indicates that, once the integrated Ekman transport exceeds 2 × 10¹² m³ (which roughly corresponds to the volume of an eddy), the Kuroshio intrusion expands and an eddy shedding event occurs within 1 month. We infer that the Ekman drift of the northeasterly monsoon pushes the Kuroshio intrusion into the SCS, creates a net westward transport into the Strait, and leads to an eddy detachment from the Kuroshio.     

The Kuroshio East of Taiwan and in the East China Sea and the currents East of Ryukyu Islands during early summer of 1996

Using hydrographic data and moored current meter records and the ADCP observed current data during May–June 1996, a modified inverse method is applied to calculate the Kuroshio east of Taiwan and in the East China Sea and the currents east of Ryukyu Islands. There are three branches of the Kuroshio east of Taiwan. The Kuroshio in the East China Sea comes from the main (first) and second branches of the Kuroshio east of Taiwan. The easternmost (third) branch of the Kuroshio flows northeastward to the region east of Ryukyu Islands. The net northward volume transports of the Kuroshio through Section K₂ southeast of Taiwan and Section PN in the East China Sea are 44.4×10⁶ and 27.2×10⁶ m³s⁻¹, respectively. The western boundary current east of Ryukyu Islands comes from the easternmost branch of the Kuroshio east of Taiwan and an anticyclonic recirculating gyre more east, making volume transports of 10 to 15×10⁶ m³s⁻¹. At about 21°N, 127°E southeast of Taiwan, there is a cold eddy which causes branching of the Kuroshio there.     

2002年春季吕宋海峡海流:观测与改进逆模式计算

基于2002年春季航次在吕宋海峡海域锚碇测流站(20°49'57"N,120°48'12"E)200,500与800m处锚碇测流以及CTD观测,采用改进逆方法对调查海域进行海流计算.(1)主要观测的结果:1)在200m处,观测期间海流平均速度为(47.4cm/s,346°).在500m处,海流观测期间平均速度为(20.3cm/s,350°).这些都表明黑潮在吕宋海峡锚碇测流站200和500m处向西北方向入侵南海.2)在800m处,海流观测期间平均速度为(1.2cm/s,35°),它的方向为东北向.比较每层实测流结果,表明800m层海流状况与200和500m层流况不同.3)在观测期间,200,500和800m处,日平均流速在4月皆比3月时要强.4)在调查海区西部的中间区域存在一个高密、冷水中心(HDCW),其中心位置位于断面A的水文站3附近.5)在调查海区东南区域存在一个低密、暖水(LDWW)中心,其中心位置位于断面B的水文站8附近.(2)主要计算结果:1)通过断面B的偏北方向与偏南方向的流量分别为32.48×106m3/s(包括反气旋涡的流量)与3.34×106m3/s.因此通过断面B的净北向流量为29.14×106m3/s.2)通过断面A的东向与西向的流量分别为16.71×106m3/s与8.57×106m3/s(包括气旋涡的流量).因此,通过断面A的净东向流量为8.14×106m3/s.3)通过断面M北向的净流量为24.68×106m3/s.4)黑潮通过断面M后分为主流和一个支流,其主流,流量为16.54×106m3/s,流向断面C的东部分.主流通过断面C的东部分后,最后流向台湾以东海域.而其一个分支,净流量为8.14×106m3/s,在一个高密、冷水中心(HDCW)的区域以东作气旋式弯曲,然后向西北方向通过断面C的西部.因此,黑潮在断面C有两个流核.5)比较计算得到的在锚碇测流站M附近流方向与在200与500m处观测流方向为西北向,它们甚为一致.6)在断面B西侧位于550m以深水层南海水可能缓慢地从西北流向东南,通过断面B的南向流量大约为3.34×106m3/s.     

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。     

An anticyclonic eddy in the intermediate layer of the Luzon Strait in Autumn 2005

The complicated flow pattern in the intermediate layer of the Luzon Strait could directly affect the efficiency of the water and energy exchange between the South China Sea (SCS) and the North Pacific. Here we present a subsurface anticyclonic eddy in the Luzon Strait deduced using observations conducted in October 2005. On the basis of the hydrographic and current measurements, an anticyclonic eddy was found in the intermediate layer, i.e., about 26.8–27.3σ_θ, 500–900 m. It captures part of the SCS Intermediate Water outflow in the northern Luzon Strait, and carries it to flow southward and then westward back into the SCS in the southern Luzon Strait, with volume transport of about 1.9 × 10⁶ m³ s⁻¹. The simulated results from Hybrid Coordinate Ocean Model also suggest the existence of this anticyclonic eddy that develops and lingers for a month long.     

2001年冬春转换期间南海东北部水文和环流特征

根据2001年3月份南海东北部航次调查温、盐资料,分析了2001年冬末春初南海东北部温、盐结构和环流的特征.分析结果表明:观测期间南海东北部环流主要受一次海盆尺度气旋型冷环流支配,冷环流呈现双核结构,垂向尺度接近1000 m.吕宋海峡内侧断面的水交换在600 m以浅海水流入南海,在断面南部(20°N以南)中层和深层有流出,断面法向地转流向西净输运量为6.9×106m3/s;直接的黑潮入侵不超过120.5°E,但有部分的黑潮水沿陆坡达到台湾岛西南部海域,并更有一部分逸入东沙岛以西海域,与南海水混合变性.     

2002年4～5月琉球群岛两侧海流的研究

基于日本气象厅“长风丸”调查船在2002年4～5月航次期间的CTD资料,结合卫星风场资料,采用改进逆方法计算了琉球群岛两侧海域各断面的流速和流量分布,并分析卫星跟踪浮标资料和同期的卫星高度计资料,得出下面一些主要结论:(1)黑潮流速在PN断面上只有一个流核.通过断面PN的净东北向流量约为34.7×106m3/s,此流量包括台湾暖流、东海黑潮和黑潮以东的反气旋涡的流量.(2)黑潮流速在断面TK上有两个流核,通过断面TK净东向的流量为25.6×106m3/s,黑潮通过海峡后流向断面ASUKA.(3)冲绳岛东南海区琉球海流的流量约为8.8×106m3/s,并流向断面AM.(4)奄美大岛以东的北向海流的流量为12.7×106m3/s,并流向断面ASUKA.在断面ASUKA东南部出现一个中尺度反气旋涡,直径约240 km,其流量约为28.5×106m3/s.(5)四国以南黑潮第一层水体基本来源于通过吐噶喇海峡的黑潮,第二、三层水体来自吐噶喇海峡和奄美大岛以东海域的流量大致相当,而第四层的流量则主要来自于奄美大岛以东海域.(6)浮标资料显示,奄美大岛以东的海流部分来自于断面AM以东海区,并通过断面ASUKA.     

2000年东海黑潮和琉球群岛以东海流的变异Ⅰ.东海黑潮及其附近中尺度涡的变异

基于日本“长风丸”调查船在2000年5个航次水文资料及同时期QuikSCAT风场资料,采用改进逆方法计算了东海黑潮的流速与流量等,获得了这5个航次期间的主要结果:(1)在东海海区风速1~2月比其他月份时大,风海流也最强.只在7月表层风海流为北向,加强了黑潮流速.(2)表层最低盐度值夏季时最小,1~2月时最大.这再次表明,夏季时长江冲淡水向东北方向扩散,冬季时基本上向南,其他季节在上述两者之间.(3)PN断面流速结构及其变化:黑潮流核在1~2,10和11月时有两个,在4和7月皆只有1个.黑潮主流核在1月位于计算点9,在4,7,10与11月都位于计算点8,即向陆架方向移动.(4)黑潮在TK断面出现多流核结构特性.11月主流核出现在TK断面中部,存在于水深大于1 200 m区域,其余月份主流核皆出现在TK断面北部,存在于深度400m以浅水层.(5)通过PN断面的净东北向流量在11月最大,为28.1×106m3/s,7月时其次,10月时最小,为24.6×106m3/s.通过PN断面的净东北向流量年平均值为26.4×106m3/s.(6)1~2,4,7与10月在PN断面以东都出现暖的、反气旋式涡,10月份时,反气旋式涡最强.只在11月时出现弱的、气旋式涡.黑潮以东反气旋涡加强时,黑潮流量似乎减小(例如10月);相反,当黑潮以东反气旋涡减弱(例如7月)或者代之出现气旋涡时(例如11月),黑潮流量似乎增大.10和11月在PN断面附近流态的比较,揭示了环流变化较大,这进一步表明,黑潮和其附近中尺度涡的相互作用是重要的.(7)通过TK断面的净东向流量,11月最大,7月其次,10与1~2月最小.通过TK断面净东向流量年平均值为21.9×106m3/s.(8)通过A断面的北向流量在1~2与4月较大,分别为3.5×106与3.1×106m3/s,7月最小.通过A断面的年平均北向流量约为2.7×106m3/s,这表明,在2000年1~2与4月通过对马暖流的流量最大,7月时最小.