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 Dataset of Global Ocean Surface Currents for 1999-2007 Derived from Argo Float Trajectories: A Comparison with Surface Drifter and TAO Measurements

A dataset of surface current vectors with error estimate from 1999 to 2007 is derived from the trajectories of the Array for Real-time Geostrophic Oceanography (Argo) drifting on surface over the global ocean. The error of the estimated surface currents is about 4.7 cm s-1 which is equivalent to the accuracy of the currents determined from the surface drifters. Geographically, the Argo-derived surface currents can fill many gaps left by the Global Drifter Program due to the greater number of floats, and can provide a complementary in situ observational system for monitoring global ocean surface currents. The surface currents from the Argo floats are compared with the surface drifter-derived currents and the Tropical Atmosphere Ocean program (TAO) measurements. The comparisons show good agreement for both the current amplitude and the direction of surface currents. Results indicate the feasibility of obtaining ocean surface currents from the Argo array and of combining the surface currents from Argo and the ocean surface drifters for in situ mapping of the global surface currents. The authors also make the dataset available to users of interest for many types of applications.

Surface circulation patterns observed by drifters in the Yellow Sea in summer of 2001,2002 and 2003

In summer of 2001, 2002 and 2003, ten, six and seventeen satellite-tracked surface drifters with drogues centered at 15 and 4 m were deployed, respectively, in the southern Yellow Sea (YS). 23 drifters of them transmitted useful data of at least 30 days. The wind-driven component of the drift was removed from the original drift velocity of drifters. The wind data used are from NCEP (National Center for Environmental Prediction), USA.Trajectories and drift velocities of the 23 drifters depicted the upper circulation structure in the southern YS.There exists an anti-cyclonic eddy with a mean speed and radius of 0.063 m/s and 50km in the central southern YS, whose center lingered within 35.3-36.0°N / 123.5-124.0°E. Showed by 6 drifters, a basin-scale elliptic cyclonic gyre with a mean speed of 0.114 m/s, long and short radius of 250 and 200 km surrounds the anti-cyclonic eddy. In the southwestern part of the southern YS has obvious frontal eddy activities within about100 km with a mean speed about 0.076 m/s. All the drifters passing Korean coast were staggering for more than10 days west of a protruding cape of central Korea. A small-scale cyclonic eddy centered at around 120.5°E/35.1°N with a mean speed of 0.048 m/s was observed in western part of the southern YS.

Observations of near surface current at the Luzon Strait in winter

One hundred and ninety-one Argos satellite-tracked drifters deployed at the Luzon Strait in winter during 1991 to 2004 were analyzed to understand the near surface current in northern South China Sea (SCS). Several major track patterns of these drifters have been found. There are:(1)shelf slope landing way (SLW); (2)deep basin way (DBW);(3) weak loop current pattern;(4) northward movement directly driven by the Kuroshio. These observations show the effects of the basin scale gyre circulation, mesoscale eddies and the Kuroshio on the drifters'ovement.

Surface currents measured by GPS drifters in Daya Bay and along the eastern Guangdong coast

GPS-based surface drifters were used to investigate the surface currents in Daya Bay and along the eastern Guangdong coast in China.Surface current vectors were measured based on the GPS location and corresponding time information sent by drifters through the mobile phone network.The analysis of data from 120 drifters,deployed in late spring 2018 in the case-study region,shows that the drifters are generally capable of capturing the surface(tidal and residual)currents.The drifter trajectories suggest an anticlockwise surface current inside Daya Bay and a north-eastward current along the eastern Guangdong coast,where the coastal current along the eastern Guangdong coast is faster than that inside Daya Bay.The surface currents in the investigated region follow an irregular semidiurnal cycle due to the influence of the tidal current,while the currents inside Daya Bay are strongly affected by the topography.According to the harmonic analysis,an irregular semidiurnal type of tidal current is evident at a study grid inside Daya Bay,with an Eulerian residual current speed of 9.0 cm/s and a direction of 276°.The Lagrangian residual current outside Daya Bay moves north-eastward with a mean speed of 22 cm/s along the eastern Guangdong coast,while the current inside Daya Bay moves northward to the bay head with a mean speed of about 8.0 cm/s,which agrees well with the one reported in other literatures.

利用漂流浮标资料对黑潮及其邻近海域表层流场及其季节分布特征的分析研究

利用1987年以来WOCE项目及我国自行投放或进入黑潮及其邻近海域（15°-36°N,114°-135°E）的共计323个卫星跟踪海表面漂流浮标资料,得到全年平均及季节平均的浮标轨迹及（1/4）°×（1/4）°格点平均的表层流矢量结果。分析认为：对于全年平均的表层流场,黑潮表层流路主要表现了对大洋西边界地形的适应,并呈现出6个较大的弯曲,其中在反气旋型弯曲处都发生分支或入侵现象、气旋型弯曲处这种现象却不明显。对于季节平均的表层流场,黑潮表层不同流段分别表现出各自显著的季节差异：吕宋海峡附近海域,表层水向南海的入侵只发生在秋、冬两季,而春、夏两季却不发生;在台湾以东海域,黑潮表层流路与黑潮右侧反气旋涡的存在与否密切相关,春季没有涡旋存在时,黑潮表层流路常出现气旋式大弯曲,其他三个季节反气旋涡存在时,黑潮表层流路相对平直;在台湾东北海域,黑潮表层水向东海南部陆架区的入侵以秋、冬季最强,春季次之,而夏季几乎不发生;在赤尾屿以北的东海黑潮中段,黑潮流动比较稳定,其表层平均流径走向由偏北到偏东依次约为冬（北偏东30°）、春（北偏东33°）、秋（北偏东38°）、夏（北偏东45°）;流路宽度由宽至窄依次约为秋（90 km）、春（80 km）、冬（70 km）、夏（60 km）,而流速由大至小依次为夏、春、秋、冬,且各季节都表现出北段流速大于南段的现象;在九州西南海域,春、秋两季黑潮表层水发生明显的向北入侵,入侵的黑潮水与东海外陆架水共同成为对马暖流的一部分来源,而夏季这种现象不明显,九州西南海域黑潮表层流路北界的位置以秋季最为偏北（但最北不超过31°N）、流路也最宽;在琉球群岛外缘海域,南半部基本没有北上的表层流存在,只有在冲绳群岛-奄美群岛以东海区,秋、夏、春三季表层反气旋涡旋都比较活跃,在涡旋的西侧有顺着冲绳群岛-奄美群岛的东北向流,其中秋季最为明显。这些结果可以为黑潮及其邻近海域的深入研究提供较为客观、直接的参考。

利用南大洋漂流浮标数据评估AMSR-E SST

利用AOML(Atlantic Oceanographical and Meteorological Laboratory)SVP漂流浮标的海表面温度数据,针对30°S以南的南大洋海域,对目前主要使用的微波遥感产品(AMSR-E,Ad-vanced Microwave Scanning Radiometer for the Earth Observing System)反演的SST进行了较为系统的评估。结果表明,AMSR-E SST比浮标数据偏冷,偏差为-0.01℃,标准差为0.70℃。夏季的偏差为0.004℃,标准差为0.64℃;冬季的偏差为-0.06℃,标准差为0.75℃,冬季的偏差和标准差较大。温差ΔT受流速影响,随着流速的增大而减小,且这种趋势在夏季更为显著。具备托伞结构的浮标与总体情况基本一致,而无托伞结构的浮标受流速的影响要大一些。同时,温差ΔT受水汽的影响,随着水汽的增加而减小,且这种影响在冬季更大一些。进一步对4个穿极和绕极浮标的追踪分析表明,温差ΔT受大洋海流系统的影响显著。在海流大的大西洋边界流和南极绕极流中,温差ΔT的不确定性要明显大于总体情况。

北斗一号卫星导航定位系统在抛弃式海洋移动观测平台的应用

作为抛弃式海洋移动观测平台,自持式剖面探测漂流浮标和海表面漂流浮标已经为国际上大量使用,该两类平台一般采用Argos卫星系统定位和传输数据。随着我国具有全部自主知识产权的北斗系统的逐步完善和发展及通信单元的小型化和低功耗化,北斗系统取代Argos系统,成为两类平台的数据传输和定位手段成为可能。文章简要介绍了自持式剖面探测漂流浮标和海表面漂流浮标的技术发展及我国北斗系统的发展情况,重点介绍了具有全部自主知识产权的采用北斗系统的C-Argo浮标和海表面漂流浮标的研制和应用情况。

台湾东北部黑潮表层水入侵东海陆架的季节变化规律

基于1998-2011年进入台湾东北部的WOCE-SVP（World Ocean Circulation Experiment -Surface Velocity Programme）计划的Argos浮标运行轨道数据，分析了台湾东北部的环流特征、黑潮表层水入侵东海陆架的季节变化规律。结果表明：在春夏季，黑潮表层水入侵仅限于陆架外缘，而在秋冬季，黑潮表层水可深入东海陆架或进入台湾海峡。自黑潮区入侵至100 m和150 m等深线的浮标数量在秋冬季较多，春夏季较少。台湾海峡的浮标轨迹在春夏季几乎皆为北向，在秋冬季皆为南向。在秋季，东海中部和南部陆架会在黑潮西侧出现逆流和涡旋。可见，台湾东北部环流具有显著的季节特征；黑潮表层水入侵东海陆架在秋冬季较强，春夏季较弱。本研究采用最新的Argos浮标数据，揭示了台湾东北部黑潮入侵东海陆架的季节变化规律。

南极绕极流的表层环流结构和能量分布特征

利用历史的表面漂流浮标资料研究了南极绕极流的平均结构、变化规律和能量特征。强劲的南极绕极流沿着纬向从西向东流动,并伴随着复杂多变的海洋锋面,主导着整个南大洋的海洋环流系统。首先,标准方差椭圆表明,阿加勒斯回流和东澳大利亚暖流是南极绕极流重要的流量补充。在南半球的冬季,南极绕极流的流速随着西风的增强而增强。在南极绕极流经向摆动的影响下,流核上的经向流速比纬向流速具有更加不稳定的特征。另外,南极绕极流从非洲南部开始自西向东逐渐减弱。其次,从能量的角度讨论了南极绕极流的细节特征。平均动能、扰动动能及其均方根在流核区域都很强,扰动动能和平均动能比值的趋势恰恰相反,强(弱)能量分布区域的涡旋耗散反而比较弱(强)。除了扰动动能和平均动能的比值之外,所有的能量形式都呈现了从西向东减弱的趋势。涡动耗散对南大洋北部的平均动能影响更大。

Monsoonal impact on circulation pathways in the Indian Ocean

Monsoon driven water mass exchange between the Bay of Bengal(Bo B) and Arabian Sea(AS) is the common experience. However, it is not yet firmly confirmed that the exchange pathway is either passing through southern tip of Sri Lanka or Palk Strait. Local circulation patterns impact the pathways followed by the East Indian Coastal Currents(EICC) that drive exchange, thereby modulating mixing and water mass transformation in the Bay of Bengal around Sri Lanka. In this study, observations from surface drifters were incorporated with the satellite derived data to understand the monsoonal impact on circulation patterns in the Indian Ocean. This was the first multi-national scientific effort which was conducted in the Bo B and AS during 2013 to 2015 to understand the monsoonal impact on circulation patterns in the complex region. The results indicated that seasonally reversing monsoonal currents of southern Sri Lanka, traced by the wintertime freshwater export pathways of the EICC. The deflection of monsoon currents running along the east coast of Sri Lanka by forming cyclonic and anti-cyclonic eddies, which influence the mixing and stirring associated with these flows. Results further indicate the low salinity cold water flows from the Bo B to AS along the western boundary of the Bo B during northeast monsoon. In the same way, reverses the phenomena during southwest monsoon, transporting high salinity warm water from AS to the Bo B. This maintain the bay status which occurred due to freshwater influx from large rivers and high saline water from AS. However, no evidences were observed for the exchange through Palk Strait during the study.Also, there are some mis-matches in in-situ and remotely sensed measurements which imply the necessity of systematic observation system for the complex region as an alternative approach.

Dynamical features of near-inertial motions in global ocean based on the GDP dataset from 2000 to 2019

Based on the latest oceanic surface drifter dataset from the global drifter program during 2000–2019,this study investigated the global variation of relative frequency shift(RFS),near-inertial energy(NIE)and inverse excess bandwidth(IEB)of near-inertial motions,and analyzed their relations with oceanic mesoscale dynamics,relative vorticity and strain.Compared with previous works,we have some new findings in this study:(1)the RFS was high with negative values in some regions in which we found a significant blue shift of the RFS in the equatorward of 30°N(S)and from 50°N to 60°N in the Pacific,and a red shift in the western boundary currents and their extension regions,the North Atlantic and the Antarctic Circumpolar Current regions;(2)more peak values of the NIE were found in global regions like the South Indian Ocean,the Luzon Strait and some areas of the South Ocean;(3)the global distribution of the IEB were characterized by clear zonal bands and affected by vorticity and wind field;(4)the RFS was elevated as the absolute value of the gradient of vorticity increased,the IEB did not depend on the gradient of vorticity,and the eddy kinetic energy(EKE)weakened with the decrease of the absolute value of RFS;(5)the NIE decreased with increasing absolute value of the relative vorticity and the gradient of vorticity,but it increased with increasing strain and EKE when EKE was larger than 0.0032 m2/s2.

南印度洋表层副热带环流的漂流示踪

基于历史表层漂流浮标数据,利用轨迹跟踪方法分析了南印度洋表层副热带环流的平均态特性.浮标路径反映出南印度洋海水由高纬向低纬输运的过程大体可分为2种:海水沿南印度洋东边界北上,汇入南赤道流后绕过马达加斯加岛北侧,沿非洲东岸跨越赤道进入北半球;或者由南印度洋中部北上,受南赤道流影响转向,到达马达加斯加岛东部后返回南印度洋构成副热带环流.漂流浮标获得的流速和能量结果表明,部分海区流的空间变率十分显著,如阿古拉斯回流区、马达加斯加北部、南印度洋西部海盆和澳大利亚西侧海区等.特别地,虽然可能受到如季节变化和涡旋扰动等因素的干扰,在漂流浮标拉格朗日式的观测下没有发现显著的副热带逆流,但是可以通过平均动能和涡动能分布观察到逆流的微弱特征.此外,基于浮标示踪,还反推留尼汪岛附近漂流浮标的可能来源,得到其沿南副热带环流的3种移动路径,这对海上搜索具有现实指示意义.

Variation of the Kuroshio intrusion pathways northeast of Taiwan using the Lagrangian method

The seasonal variations of the Kuroshio intrusion pathways northeast of Taiwan were investigated using observational data from satellite-tracked sea surface drifters and a numerical particle-tracking experiment based on a high-resolution numerical ocean model. The results of sea surface drifter data observed from 1989 to 2013 indicate that the Kuroshio surface intrusion follows two distinct pathways: one is a northwestward intrusion along the northern coast of Taiwan Island, and the other is a direct intrusion near the turn of the shelf break. The former occurs primarily in the winter, while the latter exists year round. A particle-tracking experiment in the high-resolution numerical model reproduces the two observed intrusion paths by the sea surface drifters. The three-dimensional structure of the Kuroshio intrusion is revealed by the model results. The pathways, features and possible dynamic mechanisms of the subsurface intrusion are also discussed.