An introduction to the South China Sea throughflow: Its dynamics, variability, and application for climate

The South China Sea throughflow (SCSTF) involves the inflow through the Luzon strait and the outflow through the Karimata, Mindoro, and Taiwan straits. Recent studies have suggested that the SCSTF act as a heat and freshwater conveyor, playing a potentially important role in regulating the sea surface temperature pattern in the South China Sea and its adjoining tropical Indian and Pacific Oceans. In this introductory paper, we attempt to convey the progress that has recently been made in understanding the SCSTF. We first provide an overview of existing observations, theories, and simulations of the SCSTF. Then, we discuss its interaction with the Pacific western boundary current and Indonesian throughflow. Finally, we summarize issues and questions that remain to be addressed, with special reference to the SCSTF's dynamics, variability, and implication for climate.     

Implication of the South China Sea Throughflow for the Interannual Variability of the Regional Upper-Ocean Heat Content

In this study the interannual variability of the upper-ocean heat content in the South China Sea (SCS) was revisited using simple ocean data assimilation (SODA) combined with objective analyzed data sets that included the horizontal and vertical structures.The results confirmed that the upper-ocean heat content in the SCS is lower than normal during the mature phase of El Nin o events,and two super El Nin o events,1982/1983 and 1997/1998 were also included.The variability of the heat content was consistent with the variability of the dynamic height anomalies.The SCS throughflow (SCSTF) plays an important role in regulating the interannual variability of the heat content,especially during the mature phase of El Nin o events.     

Impact of the South China Sea Throughflow on the Pacific Low-Latitude Western Boundary Current: A Numerical Study for Seasonal and Interannual Time Scales

Prior studies have revealed that,as a part of the Pacific tropical gyre,the South China Sea throughflow(SCSTF) is strongly influenced by the Pacific low-latitude western boundary current(LLWBC).In this study,ocean general circulation model(OGCM) experiments with and without connection to the South China Sea(SCS) were performed to investigate the impact of the SCSTF on the Pacific LLWBC.These model experiments show that if the SCS is blocked,seasonal variability of the Kuroshio and Mindanao Current becomes stronger,and the meridional migration of the North Equatorial Current(NEC) bifurcation latitude is enhanced.Both in seasonal and interannual time scales,stronger Luzon Strait transport(LST) induces a stronger Kuroshio transport combined with a southward shift of the NEC bifurcation,which is unfavorable for a further increase of the LST;a weaker LST induces a weaker Kuroshio transport and a northward shifting NEC bifurcation,which is also unfavorable for the continuous decrease of the LST.     

Covariation of the Indonesian Throughflow and South China Sea Throughflow Associated with the 1976/77 Regime Shift

Changes in the Indonesian Throughflow(ITF) and the South China Sea throughflow—measured by the Luzon Strait Transport(LST)—associated with the 1976/77 regime shift are analyzed using the Island Rule theory and the Simple Ocean Data Assimilation dataset.Results show that LST increased but ITF transport decreased after 1975.Such changes were induced by variations in wind stress associated with the regime shift.The strengthening of the easterly wind anomaly east of the Luzon Strait played an important role in ...     

Three inflow pathways of the Indonesian throughflow as seen from the simple ocean data assimilation

The SODA product is used to investigate three Indonesian throughflow (ITF) branches: the flow through the Makassar Strait; through the South China Sea; and through the eastern Indonesian basins. The results reveal strong interannual variation in the Makassar Strait and the eastern Indonesian basins throughflow. Inspection of vertically integrated dynamic height (0–1000 db), a proxy of transport function, suggests that this interannual variation can be traced to the New Guinea Coastal Current, indicative of a strong influence of the South Pacific. The vertically integrated dynamic height along the south Java coast is related to variation in the North Pacific and in particular near the east coast of Mindanao Island, whereas the vertically integrated dynamic height along the coast of West Australia is related to variation in the South Pacific, and in particular near the coast of New Guinea. The integrated dynamic height difference between the Java and New Guinea coast appears to be a good proxy of ITF transport on the interannual time scale. Regression analysis shows a phase dependence of the three ITF pathways on the Nino3.4 index. Decoupling of current anomalies between the surface and subsurface layers is identified in the developing and mature phase of El Nino, reflecting different effects of local and remote forcing through oceanic pathways at the Makassar Strait and eastern Indonesian basins.     

Climatology and variability of the Indonesian Throughflow in an eddy-permitting oceanic GCM

A quasi-global eddy permitting oceanic GCM, LICOM1.0, is run with the forcing of ERA40 daily wind stress from 1958 to 2001. The modelled Indonesian Throughflow (ITF) is reasonable in the aspects of both its water source and major pathways. Compared with the observation, the simulated annual mean and seasonal cycle of the ITF transport are fairly realistic. The interannual variation of the tropical Pacific Ocean plays a more important role in the interannual variability of the ITF transport. The relationshipbetween the ITF and the Indian Ocean Dipole (IOD) also reflects the influence of ENSO. However, the relationship between the ITF transport and the interannual anomalies in the Pacific and Indian Oceans vary with time. During some years, (e.g., 1994), the effect of a strong IOD on the ITF transport is more than that from ENSO.     

渤海西岸边界层东风与暴雪天气的机理分析

2008年12月20—21日和2010年1月3日天津地区分别出现了历史同期罕见的暴雪天气。为了提高对这种极端天气发生机理的认识,利用多种资料对这两次天气过程进行了分析。结果表明：两次暴雪过程均属于回流型降雪,但环流形势和影响系统的演变却不尽相同。影响系统分别为高空横槽（高空槽）、850 hPa切变（850 hPa低涡切变）和地面倒槽（地面气旋）,水汽源自700 hPa西南气流和边界层东风的水汽输送。由于两次过程均与边界层东风相伴,特别对渤海西岸边界层东风对降雪天气的影响和作用进行探讨,表明偏东风不仅为本地输送一定量级的水汽,同时这种具有冷湿特征的东风还会与内陆具有暖湿结构的偏南风形成地面辐合线,加强地面的动力抬升作用,产生上升运动,有利于雨雪天气的加强和维持,因此可以认为边界层东风对暴雪的发生发展起到了显著的作用。     

渤海西岸边界层东风与暴雪天气的机理分析

2008年12月20-21日和2010年1月3日天津地区分别出现了历史同期罕见的暴雪天气。为了提高对这种极端天气发生机理的认识,利用多种资料对这两次天气过程进行了分析。结果表明：两次暴雪过程均属于回流型降雪,但环流形势和影响系统的演变却不尽相同。影响系统分别为高空横槽（高空槽）、850 hPa切变（850 hPa低涡切变）、地面倒槽（地面气旋）,水汽源自700 hPa西南气流和边界层东风的水汽输送。由于两次过程均与边界层东风相伴,特别对渤海西岸边界层东风对降雪天气的影响和作用作了探讨,表明偏东风不仅为本地输送一定量级的水汽,同时这种具有冷湿特征的东风还会与内陆具有暖湿结构的偏南风形成地面辐合线,加强地面的动力抬升作用,产生上升运动,有利于雨雪天气的加强和维持,因此可以认为边界层东风对暴雪的发生发展起到了显著的作用。     

The seasonal variation of the upper layers of the South China Sea (SCS) circulation and the Indonesian through flow (ITF): An ocean model study

The upper layer, wind-driven circulation of the South China Sea (SCS), its through-flow (SCSTF) and the Indonesian through flow (ITF) are simulated using a high resolution model, FVCOM (finite volume coastal ocean model) in a regional domain comprising the Maritime Continent. The regional model is embedded in the MIT global ocean general circulation model (ogcm) which provides surface forcing and boundary conditions of all the oceanographic variables at the lateral open boundaries in the Pacific and Indian oceans. A five decade long simulation is available from the MITgcm and we choose to investigate and compare the climatologies of two decades, 1960–1969 and 1990–1999.The seasonal variability of the wind-driven circulation produced by the monsoon system is realistically simulated. In the SCS the dominant driving force is the monsoon wind and the surface circulation reverses accordingly, with a net cyclonic tendency in winter and anticyclonic in summer. The SCS circulation in the 90s is weaker than in the 60s because of the weaker monsoon system in the 90s. In the upper 50 m the interaction between the SCSTF and ITF is very important. The southward ITF can be blocked by the SCSTF at the Makassar Strait during winter. In summer, part of the ITF feeds the SCSTF flowing into the SCS through the Karimata Strait. Differently from the SCS, the ITF is primarily controlled by the sea level difference between the western Pacific and eastern Indian Ocean. The ITF flow, consistently southwestward below the surface layer, is stronger in the 90s.The volume transports for winter, summer and yearly are estimated from the simulation through all the interocean straits. On the annual average, there is a ∼5.6 Sv of western Pacific water entering the SCS through the Luzon Strait and ∼1.4 Sv exiting through the Karimata Strait into the Java Sea. Also, ∼2 Sv of SCS water enters the Sulu Sea through the Mindoro Strait, while ∼2.9 Sv flow southwards through the Sibutu Strait merging into the ITF. The ITF inflow occurs through the Makassar Strait (up to ∼62%) and the Lifamatola Strait (∼38%). The annual average volume transport of the ITF inflow from the simulation is ∼15 Sv in the 60s and ∼16.6 Sv in the 90s, very close to the long term observations. The ITF outflow through the Lombok, Ombai and Timor straits is ∼16.8 Sv in the 60s and 18.9 Sv in the 90s, with the outflow greater by 1.7 Sv and 2.3 Sv respectively. The transport estimates of the simulation at all the straits are in rather good agreement with the observational estimates.We analyze the thermal structure of the domain in the 60s and 90s and assess the simulated temperature patterns against the SODA reanalysis product, with special focus on the shallow region of the SCS. The SODA dataset clearly shows that the yearly averaged temperatures of the 90s are overall warmer than those of the 60s in the surface, intermediate and some of the deep layers and the decadal differences (90s − 60s) indicate that the overall warming of the SCS interior is a local effect. In the simulation the warm trend from the 60s to the 90s in well reproduced in the surface layer. In particular, the simulated temperature profiles at two shallow sites at midway in the SCSTF agree rather well with the SODA profiles. However, the warming trend in the intermediate (deep) layers is not reproduced in the simulation. We find that this deficiency is mostly due to a deficiency in the initial temperature fields provide by the MITgcm.     

A Note on the South China Sea Shallow Interocean Circulation

1. IntroductionThe South China Sea (SCS) has many channelsconnecting with the outer oceans/seas (Fig. 1). Thewidest and deepest channel is the Luzón Strait, whichis the main entrance to the SCS from the WesternPacific Ocean, having a sill depth of about 2500 m.On the north, the Taiwan Strait connects with theEast China Sea, with a sill depth of about 70 m. Inthe vicinity of Mindoro Island, there are a numberof channels connecting the SCS with the Sulu Sea.The main channel is the M…     

Interocean circulation and heat and freshwater budgets of the South China Sea based on a numerical model

The South China Sea (SCS) interocean circulation and its associated heat and freshwater budgets are examined using the results of a variable-grid global ocean model. The ocean model has a 1/6° resolution in the SCS and its adjacent oceans. The model results from 1982 to 2003 show that the western Pacific waters enter the SCS through the Luzon Strait with an annual mean volume transport of 4.80 Sv, of which 1.71 Sv returns to the western Pacific through the Taiwan Strait and East China Sea and 3.09 Sv flows toward the Indian Ocean. The heat in the western Pacific is transported to the SCS with a rate of 0.373 PW (relative to a reference temperature 3.72 °C), while the total heat transport through the outflow straits is 0.432 PW. The net heat transport out of the SCS is thus 0.059 PW, which is balanced by a mean net downward heat flux of 17 W/m² across the SCS air–sea interface. Therefore, the interocean circulation acts as an “air conditioner”, cooling the SCS and its overlaying atmosphere. The SCS contributes a heat transport of 0.279 PW to the Indian Ocean, of which 0.240 PW is from the Pacific Ocean through the Luzon Strait and 0.039 PW is from the SCS interior gained from the air–sea exchange. The Luzon Strait salt transport is greater than the total salt transport leaving the SCS by 3.97 Gg/s, implying a mean freshwater flux of 0.112 Sv (or 3.54 × 10¹² m³/year) from the land discharge and P − E (precipitation minus evaporation). The total annual land discharge to the SCS is estimated to be 1.60 × 10¹² m³/year, the total annual P − E over the SCS is thus 1.94 × 10¹² m³/year, equivalent to a mean P − E of 0.55 m/year. The SCS freshwater contribution to the Indian Ocean is 0.096 Sv. The pattern of the SCS interocean circulation in winter differs greatly from that in summer. The SCS branch of the Pacific-to-Indian Ocean throughflow exists in winter, but not in summer. In winter this branching flow starts at the Luzon Strait and extends to the Karimata Strait. In summer the interocean circulation is featured by a north-northeastward current starting at the Karimata Strait and extending to the Taiwan and Luzon Straits, and a subsurface inflow from the Luzon Strait that upwells into the surface layer in the SCS interior to supply the outward transports.     

Ground-based remote sensing observation of the complex behaviour of the Marseille boundary layer during ESCOMPTE

Ground-based remote sensing systems have been used during the ESCOMPTE campaign, to continuously characterize the boundary-layer behaviour through many atmospheric parameters (wind, extinction and ozone concentration distribution, reflectivity, turbulence). This analysis is focused on the comparison of the atmospheric stratification retrieved from a UV angular ozone lidar, an Ultra High Frequency wind profiler and a sodar, above the area of Marseille, on June 26th 2001 (Intensive Observation Period 2b). The atmospheric stratification is shown to be very complex including two superimposed sea breezes, with an important contribution of advection. The temporal and spatial evolution of the stratification observed by the UV lidar and by the UHF radar are in good agreement although the origin of the echoes of these systems is quite different. The complexity of the dynamic situation has only partially been retrieved by a non-hydrostatic mesoscale model used with a 3 km resolution.     

斯里兰卡南部西向沿岸流在西南季风期间的动力学研究

北半球夏季,北印度洋环流主要受到西南季风流控制,将热带印度洋水体从西向东进行跨海盆输运,然而在斯里兰卡南部沿岸存在一支与西南季风流方向相反的西向沿岸流,即南斯里兰卡沿岸流（SSLCC）.本文主要利用ECCO2资料进行南斯里兰卡沿岸流的动力学特征研究.结果表明,SSLCC的形成和孟加拉湾局地环流密切相关.当斯里兰卡穹顶区（SLD）环流偏强时,斯里兰卡南部形成局地气旋式涡旋,斯里兰卡东部沿岸流在SLD西部向南流动,随着气旋式涡旋北部转向西流形成强的SSLCC.相比之下,SLD较弱时,沿岸流仅存在斯里兰卡东部沿岸,斯里兰卡东部沿岸流无法向西转向,SSLCC和西南季风流一起向东流动,其可能的主要原因是局地风应力对SLD产生的强度影响.研究还表明,SLD强度对SSLCC流向和强度有着重要影响.     

南海上层海洋热结构的年循环与半年循环

根据南海季风试验(SCSMEX)期间南海内区的三个ATLAS(Autonomous Temperature Line Acquisition System)锚碇浮标资料(1998年4月～1999年4月),采用谐波分析方法对南海上层海洋水温年循环、半年循环加以分离,发现无论在年循环还是在半年循环尺度上,18°N附近SCS1站与13°N附近SCS3站的水温变化次表层与表层呈反位相;15°20′N附近SCS2站水温变化基本上次表层与表层同位相.这说明不同区域上层海洋热变化受不同的正压与斜压模态控制.其次,SCS2、SCS3两点水温年循环振幅均在次表层达到极值;而SCS1在表层达到极大值,在100 m深度达到次极大值.3个站位水温半年循环振幅极值均出现在次表层内,这说明该层内的水温半年循环在温度变化趋势中所占的权重比在表层的权重大.     

南海夏季海流的数值模拟

用一个水平分辨率较高的区域海洋模式计算了中国海的海流。本文给出了南海７月份的上层环流的数值模拟结果。结果表明:在南海北部的陆架区，一支较强的东北向海流穿过台湾海峡流入东海；在海南岛东南和越南沿岸以东海域有一个气旋式的涡旋；南海南部被一个反气旋式的大涡旋所占据。计算得到的这些环流特征与观测结果十分一致。另外，数值模拟结果还显示出，黑潮的一个分支通过巴士海峡的南部进入南海，虽然一部分海水不断被陆架诱导流向东北，但是仍有一部分海水可以一直向西流到海南岛以东海域。     

Low frequency variations in currents on the southern continental shelf of the Caspian Sea

The Caspian Sea (CS) is the largest enclosed basin in the world, located inside the Eurasian continent in the Northern Hemisphere. Although there have been few studies of the dynamics of the coastal zone in the CS, observations show that oscillations with periods from 2–3 days to 1–3 weeks dominate. These oscillations are presumed to be related to the synoptic variability of direct wind impact and to coastally-trapped waves (CTW). Here, we describe and interpret current meter observations on the continental margins of the southern CS from 2012 to 2014 to identify and characterize CTW there. Time series analysis provides evidence for both remote and locally wind-forced eastward traveling signals with time lags consistent with CTW theory. A wind-forced model with two CTW modes is able to reproduce the structure, amplitudes, and phases of observed alongshore current fluctuations, explaining half of the variance at frequencies less than 1 cpd. Remote forcing effects are present at all times, but are most striking when the local winds are weak, as in summer. The CTW calculations also suggest that the source region for the remote forcing may extend farther north along the west coast of the CS.     

Impacts of the South China Sea Throughflow on seasonal and interannual variations of the Indonesian Throughflow

Impacts of the South China Sea Throughflow (SCST) on seasonal and interannual variations of the Indonesian Throughflow are studied by comparing outputs from ocean general circulation model (OGCM) experiments with and without the SCST. The observed subsurface maximum in the southward flow through the Makassar Strait is simulated only when the SCST, which is driven by the large-scale wind, is allowed in the model. The mean volume and heat transport by the Makassar Strait Throughflow are reduced by 1.7 Sv and 0.19 PW, respectively, by the existence of the SCST in the model. The difference is particularly remarkable during boreal winter when the SCST reaches its seasonal maximum. Furthermore, the SCST is strengthened during El Niño, leading to the weakening in the southward volume and heat transport through the Makassar Strait by 0.37 Sv and 0.05 PW, respectively. These findings from the OGCM experiments suggest that the SCST may play an important role in climate variability of the Indo-Pacific Ocean.     

南海海域海-气耦合模式及其数值模拟试验

在ＮＣＡＲ区域气候模式ＲｅｇＧＭ２和普林斯顿海洋模式ＰＯＭ基础上发展适用于区域海－气相互作用研究的区域海－气耦合模式,模式采用同步耦合、海洋模式将海表温度提供给大气模式,大气模式为海洋模式提供太阳短波辐射、感热能量、潜热通量。海洋与大气模式每１５ｍｉｎ交换一次通量。耦合过程没有使用通量校正。使用该模式对中国南海区域１９９５年５－７月大气和海洋进行了模拟试验,将模拟结果与ＣＯＡＤＳ通量强迫的模拟结果     

Laboratory studies of the effects of interrupted, sloping topography on intermediate depth boundary currents in linearly stratified fluids

Laboratory experiments are described which provide insight into the interaction of intermediate depth boundary currents (IDBCs) with interrupted sloping topography. Specifically, they contribute to the debate over meddy formation on the Iberian continental slope. The experiments were performed in a rectilinear rotating tank filled initially with a linearly-stratified fluid. A false bottom sloped away from the side-wall along which the current flowed, and was interrupted by a gap of variable length. The effects of varying gap length and rotation rate on the boundary current were observed.In the first of two sets of experiments, the current flowed above the slope, along the vertical sidewall. In the second, the current flowed along the sloping bottom. In the former, current nose speed was consistent with geostrophic predictions, but decreased in the presence of a gap in the topography. Kelvin wave radiation is postulated as a reason for this. The IDBCs exhibited vortical lateral intrusions at values of the Burger number Bu=(N₀/Ω)² at which counterpart flat-bottom studies had been stable, implying that the sloping topography had a de-stabilising effect. Energy measurements and qualitative observations suggest the intrusions were due to mixed barotropic/baroclinic instabilities, the latter dominating at higher rotation rates.In the second configuration, four distinct flows were observed, distinguished by the deformation radius:gap width ratio R_D/G^*. For a range of values of R_D/G^*, attached eddies formed at the upstream end of the gap. They remained at this position, unlike those in similar studies of surface boundary currents (Klinger, 1993). Their persistence and ability to move downstream – salient factors for meddy – formation were greater for a finite gap size than a permanent change from sloping to flat bottom.     

Summer Monsoon Impacts on Chlorophyll-a Concentration in the Middle of the South China Sea: Climatological Mean and Annual Variability

Climatological mean and annual variations of Chlorophyll-a(Chl-a) distribution,sea surface wind(SSW),and sea surface temperature(SST) from 1998 to 2008 were analyzed in the middle of the South China Sea(SCS),focusing on the typical region off the east coast of Vietnam(8.5-14°N,109.5-114°E).Based on remote sensing data and SCS summer monsoon index(SCSSMI) data,high Chl-a concentrations in the middle of the SCS in the southwest summer monsoon season(June-September) may be related to strong Ekman pumping and strong wind stress.The maximum of the monthly averaged climatological Chl-a in the summer appeared in August.According to the annual variation,there was a significant negative correlation(r =-0.42) between the SCSSMI and SST,a strongly positive correlation(r=0.61) between the SCSSMI and Chl-a,and a strongly negative correlation(r =-0.74) between the SST and Chl-a in the typical region off the east coast of Vietnam during 1998-2008.Due to the El Ni?o event specifically,the phenomena of a low Chl-a concentration,high SST and weak SCSSMI were extremely predominant in the summer of 1998.These relationships imply that the SCSSMI associated with the SST could be used to predict the annual variability of summer Chl-a in the SCS.