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1.
A three-dimensional baroclinic shelf sea model was employed to simulate the seasonal characteristics of the South China Sea (SCS) upper circulation. The results showed that: in summer, an anticyclonic eddy, after its formation between the Bashi Channel and Dongsha Islands in the northeastern SCS, moves southwestward until it disperses slowly. There exists a northward western boundary current along the east shore of the Indo-China Peninsula in the western SCS and an anticyclonic gyre in the southern SCS. But at the end of summer and beginning of autumn, a weak local cyclonic eddy forms in the Nansha Trough, then grows slowly and moves westward till it becomes a cyclonic gyre in the southern SCS in autumn. At the beginning of winter, there exists a cyclonic gyre in the northern and southern SCS, and there is a southward western boundary current along the east shore of the Indo-China Peninsula. But at the end of winter, an anticyclonic eddy grows and moves toward the western boundary after forming in the Nansha Trough. The eddy‘s movement induces a new opposite sign eddy on its eastern side, while the strength of the southward western boundary current gets weakened. This phenomenon continues till spring and causes eddies in the southern SCS.  相似文献   

2.
为了合理有效地分析和挖掘海洋涡旋移动数据中的规律和模式,本文以基于空间交互性流聚类的区域化方法为基础,提出了一种海洋涡旋移动特征的网格区域化方法。该方法以网格为统计单元,对涡旋移动数据进行组织,通过图论模型构建海洋涡旋的移动网络图,然后采用基于平均邻接的层次聚类和基于模块度的划分2个步骤,实现涡旋移动特征的区域划分。基于该算法,对1992-2011年中国南海海洋涡旋移动数据进行算法实验,结果表明,南海海洋涡旋按照其移动频繁性特征可分为越南东南部（R1）、越南东部-巴拉望岛（R2）、南海北部（R3）3个区域。其中,R1区域包含了南海西南部深海盆地区的涡旋活跃条带;R2区域体现了南海中部涡旋向西移动的活动规律;R3区域则包含了南海北部东北-西南走向条带。3个区域内冷涡和暖涡具有明显的季节性变化特征：R1和R3区域冷暖涡变化相似,暖涡在夏秋季移动最多,冬季最少,而冷涡则相反,夏秋季移动最少,随后逐渐增加,并在春季达到峰值;R2区域暖涡在春季移动最多,而冷涡在夏冬移动最多,春秋移动相对较弱。  相似文献   

3.
Using a 1.5 layer nonlinear shallow-water reduced-gravity model, we executed numerical simulations to investigate the possibility of a western boundary current (WBC) path transition due to mesoscale eddies based on the background of the Kuroshio intrusion into the South China Sea (SCS) from the Luzon Strait. Because the WBC existed different current states with respect to different wind stress control parameters, we chose three steady WBC states (loop current, eddy shedding and leaping) as the background flow field and simulated the path transition of the WBC due to mesoscale eddies. Our simulations indicated that either an anticyclonic or cyclonic eddy can lead to path transition of the WBC with different modes. The simulation results also show that the mesoscale eddies can lead to path transition of the WBC from loop and eddy shedding state to leaping state because of the hysteresis effect. The leaping state is relatively stable compared with the mesoscale eddies. Moreover, an anticyclonic eddy is more effective in producing the WBC path transition for the path transition than a cyclonic eddy. Our results may help to explain some phenomena observed regarding the path transition of the Kuroshio due to the mesoscale eddies at the Luzon Strait.  相似文献   

4.
Based on the EOF analyses of Absolute Dynamic Topography satellite data,it is found that,in summer,the northern South China Sea(SCS) is dominated by an anticyclonic gyre whilst by a cyclonic one in winter.A connected single-layer and two-layer model is employed here to investigate the dynamic mechanism of the circulation in the northern SCS.Numerical experiments show that the nonlinear term,the pressure torque and the planetary vorticity advection play important roles in the circulation of the northern SCS,whilst the contribution by seasonal wind stress curl is local and limited.Only a small part of the Kuroshio water intrudes into the SCS,it then induces a positive vorticity band extending southwestward from the west of the Luzon Strait(LS) and a negative vorticity band along the 200 m isobath of the northern basin.The positive vorticity field induced by the local summer wind stress curl is weaker than that induced in winter in the northern SCS.Besides the Kuroshio intrusion and monsoon,the water transports via the Sunda Shelf and the Sibutu Passage are also important to the circulation in the northern SCS,and the induced vorticity field in summer is almost contrary to that in winter.The strength variations of these three key factors(Kuroshio,monsoon and the water transports via the Sunda Shelf and the Sibutu Passage) determine the seasonal variations of the vorticity and eddy fields in the northern SCS.As for the water exchange via the LS,the Kuroshio intrusion brings about a net inflow into the SCS,and the monsoon has a less effect,whilst the water transports via the Sunda Shelf and the Sibutu Passage are the most important influencing factors,thus,the water exchange of the SCS with the Pacific via the LS changes dramatically from an outflow of the SCS in summer to an inflow into the SCS in winter.  相似文献   

5.
A three-dimensional baroclinic shelf sea model‘ s numerical simulation of the South China Sea (SCS) middle and deep layer circulation structure showed that: 1. In the SCS middle and deep layer, a seulhward boundary current exists along the east shore of the Indo-China Peninsula all year long.A cyclonic eddy (gyre) is formed by the current in the above sea areas except in the middle layer in spring, when an anticyclonic eddy exists on the eastern side of the current. In the deep layer, a larges-cale anticyclonic eddy often exists in the sea areas between the Zhongsha Islands and west shore of southern Luzon Island. 2. In the middle layer in snmmer and autumn, and in the deep layer in autumn and winter, there is an anticyclonic eddy (gyre) in the northeastern SCS, while in the middle layer in winter and spring, and in the deep layer in spring and snmmer, there is a cyclonic one. 3. In the middle layer,there is a weak northeastward current in the Nansha Trough in spring and snmmer, while in autumn and winter it evolves inl~ an anticyclonic eddy ( gyre), which then spreads westward l~ the whole western Nansha Islands sea areas.  相似文献   

6.
Bottom currents at about 1000 m depth in and around a submarine valley on the continental slope of the northern South China Sea were studied by a 14-month long experiment from July 2013 to September 2014. The observations reveal that bottom currents are strongly influenced by the topography, being along valley axis or isobaths. Power density spectrum analysis shows that all the currents have significant peaks at diurnal and semi-diurnal frequencies. Diurnal energy is dominant at the open slope site, which is consistent with many previous studies. However, at the site inside the valley the semi-diurnal energy dominates, although the distance between the two sites of observation is quite small(11 km) compared to a typical horizontal first-mode internal tide wavelength(200 km). We found this phenomenon is caused by the focusing of internal waves of certain frequencies in the valley. The inertial peak is found only at the open slope site in the first deployment but missing at the inside valley site and the rest of the deployments. Monthly averaged residual currents reveal that the near-bottom currents on the slope flow southwestward throughout the year except in August and September, 2013, from which we speculate that this is a result of the interaction between a mesoscale eddy and the canyon/sag topography. Currents inside the valley within about 10 mab basically flow along slope and in the layers above the 10 mab the currents are northwestward, that is, from the deep ocean to the shelf. The monthly mean current vectors manifest an Ekman layer-like vertical structure at both sites, which rotate counter-clockwise looking from above.  相似文献   

7.
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 differs 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 affected by variations of local SCS circulation,which is more strongly than in the first step in which it is affected 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.  相似文献   

8.
The method proposed by Stammer (1998) is modified using eddy statistics from altimeter observation to obtain more realistic eddy diffusivity (K) for the North Pacific. Compared with original estimates, the modified K has remarkably reduced values in the Kuroshio Extension (KE) and North Equatorial Counter Current (NECC) regions, but slightly enhanced values in the Subtropical Counter Current (STCC) region. In strong eastward flow areas like the KE and NECC, owing to a large difference between mean flow velocity and propagation velocity of mesoscale eddies, tracers inside the mesoscale eddies are transported outside rapidly by advection, and mixing length L is hence strongly suppressed. The low eddy probability (P) is also responsible for the reduced K in the NECC area. In the STCC region, however, L is mildly suppressed and P is very high, so K there is enhanced. The zonally-averaged K has two peaks with comparable magnitudes, in the latitude bands of the STCC and KE. In the core of KE, because of the reduced values of P and L, the zonally-averaged K is a minimum. Zonally-integrated eddy heat transport in the KE band, calculated based on the modified K, is much closer to the results of previous independent research, indicating the robustness of our modified K. The map of modified K provides useful informationfor modeling studies in the North Pacific.  相似文献   

9.
We addressed the mesoscale structure variation of the central South China Sea (SCS) with the measurements by a long-lived Argo float and a high-resolution ATLAS buoy during 1998–2002. T-S diagram indicates cooling and freshening events in 2000 and 2001 with lower salinity (0.5–0.8) and lower temperature (1–1.7°C). Significant decrease in the net heat flux and increase in the precipitation suggest that the cooling and freshening is due to extra forcing by the atmosphere. Additional to large year-to-year changes, intraseasonal variability is moderate in the research area. The axis of the maximum intraseasonal temperature and salinity signals are mainly located on the thermocline. Typically, amplitude and period of intraseasonal temperature is about 2°C and 40–60 days, and that of salinity is 0.3–0.5 and 35–60 days. Rapidly-changing winds, heat flux, and precipitation are critical in controlling the intraseasonal fluctuations of the mixed layer of the area. Studies on heat and freshwater balance in the mixed-layer further suggest that horizontal advection plays an important role in intraseasonal fluctuation in the upper ocean. In addition, the energetic mesoscale propagation radiated from the east boundary is linked to the intraseasonal variability in winter.  相似文献   

10.
Using a Finite-Volume Community Ocean Model, we investigated the dynamic mechanism of the South China Sea Warm Current(SCSWC) in the northern South China Sea(NSCS) during winter monsoon relaxation. The model reproduces the mean surface circulation of the NSCS during winter, while model-simulated subtidal currents generally capture its current pattern. The model shows that the current over the continental shelf is generally southwestward, under a strong winter monsoon condition, but a northeastward counter-wind current usually develops between 50-and 100-m isobaths, when the monsoon relaxes. Model experiments, focusing on the wind relaxation process, show that sea level is elevated in the northwestern South China Sea(SCS), related to the persistent northeasterly monsoon. Following wind relaxation, a high sea level band builds up along the mid-shelf, and a northeastward current develops, having an obvious vertical barotropic structure. Momentum balance analysis indicates that an along-shelf pressure gradient provides the initial driving force for the SCSWC during the first few days following wind relaxation. The SCSWC subsequently reaches a steady quasi-geostrophic balance in the cross-shelf direction, mainly linked to sea level adjustment over the shelf. Lagrangian particle tracking experiments show that both the southwestward coastal current and slope current contribute to the northeastward movement of the SCSWC during winter monsoon relaxation.  相似文献   

11.
Using 19-year satellite altimetric data, variations in the eddy kinetic energy, energy exchanges and interaction between the eddy field and mean flow are discussed for the Kuroshio south of Japan. In the seasonal cycle, the eddy kinetic energy level is a minimum in December/January and a maximum in April/May. In addition to seasonal variations, the eddy kinetic energy undergoes interannual changes. The energy transfers mainly from the mean flow to the eddy field in the Kuroshio south of Japan, and dominant energy exchanges mainly occur along the Kuroshio path south of Japan in each year from 1993 to 2011. In addition, there is often barotropic instability south of Honshu. Regarding interactions between the eddy field and mean flow, cyclonic and anticyclonic accelerations are also found along the Kuroshio path and they flank each other. There is cyclonic acceleration always imposed on southeast of Kyushu, and anticyclonic acceleration dominates south of Honshu from 2001 to mid-2005. Reynolds stress is used to explain the dynamic process of energy exchange. Furthermore, lag-correlation and linear regression analysis show that variability of the energy conversion rate and Reynolds stress involve responses to eddy acceleration at two time scales. The enhanced eddy acceleration induces large Reynolds stress, and enhanced Reynolds stress or barotropic instability further enforces energy transfer from the mean flow to the eddy field.  相似文献   

12.
Zhao  Bo  Xu  Zhenhua  Li  Qun  Min  Wenjia  Wang  Yang  Yin  Baoshu 《中国海洋湖沼学报》2022,40(2):413-427
Journal of Oceanology and Limnology - The generation and propagation characteristics of near-inertial waves (NIWs) generated spontaneously from a quasi-geostrophic anticyclonic mesoscale eddy in a...  相似文献   

13.
Using a 19-year altimetric dataset, the mean properties and spatiotemporal variations of eddies in the Kuroshio recirculation region are examined. A total of 2 001 cyclonic tracks and 1 847 anticyclonic tracks were identifi ed using a geometry-based eddy detection method. The mean radius was 57 km for cyclonic eddies and was 61 km for anticyclonic eddies, respectively, and the mean lifetime was about 10 weeks for both type eddies. There were asymmetric spatial distributions for eddy generation and eddy termination, which were domain-dependent. Mean eddy generation rates were 2.0 per week for cyclonic eddies and were 1.9 per week for anticyclonic eddies. Both type eddies tended to deform during their lifetime and had different propagation characteristics, which mainly propagated westward and southwestward with velocities 4.0–9.9 cm/s, in the Kuroshio recirculation region. Further discussion illustrates that the eddy westward speed maybe infl uenced by the combined effect of vertical shear of horizontal currents and nonlinearity of eddy. To better understand the evolution of eddy tracks, a total of 134 long-lived tracks(lifetime ≥20 weeks) were examined. Comparison between short-span eddies(lifetime ≥4 weeks and 20 weeks) and long-lived eddies is also conducted and the result shows that the short-span and long-lived eddies have similar time evolution. Finally, eddy seasonal variations and interannual changes are discussed. Correlation analysis shows that eddy activity is sensitive to the wind stress curl and meridional gradient of sea surface temperature on interannual timescales. Besides, the strength and orientation of background fl ows also have impacts on the eddy genesis.  相似文献   

14.
Wind measurements derived from QuikSCAT data were compared with those measured by anemometer on Yongxing Island in the South China Sea (SCS) for the period from April 2008 to November 2009. The comparison confirms that QuikSCAT estimates of wind speed and direction are generally accurate, except for the extremes of high wind speeds (>13.8m/s) and very low wind speeds (<1.5m/s) where direction is poorly predicted. In-situ observations show that the summer monsoon in the northern SCS starts between May 6 and June 1. From March 13, 2010 to August 31, 2010, comparisons of sea surface temperature (SST) and rainfall from AMSR-E with data from a buoy located at Xisha Islands, as well as wind measurements derived from ASCAT and observations from an automatic weather station show that QuikSCAT, ASCAT and AMSR-E data are good enough for research. It is feasible to optimize the usage of remote-sensing data if validated with in-situ measurements. Remarkable changes were observed in wind, barometric pressure, humidity, outgoing longwave radiation (OLR), air temperature, rainfall and SST during the monsoon onset. The eastward shift of western Pacific subtropical high and the southward movement of continental cold front preceded the monsoon onset in SCS. The starting dates of SCS summer monsoon indicated that the southwest monsoon starts in the Indochinese Peninsula and forms an eastward zonal belt, and then the belt bifurcates in the SCS, with one part moving northeastward into the tropical western North Pacific, and another southward into western Kalimantan. This largely determined the pattern of the SCS summer monsoon. Wavelet analysis of zonal wind and OLR at Xisha showed that intra-seasonal variability played an important role in the summer. This work improves the accuracy of the amplitude of intra-seasonal and synoptic variation obtained from remote-sensed data.  相似文献   

15.
Vertical structure and evolution of the Luzon Warm Eddy   总被引：4，自引：0，他引：4  
Eddies are frequently observed in the northeastern South China Sea (SCS). However, there have been few studies on vertical structure and temporal-spatial evolution of these eddies. We analyzed the seasonal Luzon Warm Eddy (LWE) based on Argo float data and the merged data products of satellite altimeters of Topex/Poseidon, Jason-1 and European Research Satellites. The analysis shows that the LWE extends vertically to more than 500 m water depth, with a higher temperature anomaly of 5°C and lower salinity anomaly of 0.5 near the thermocline. The current speeds of the LWE are stronger in its uppermost 200 m, with a maximum speed of 0.6 m/s. Sometimes the LWE incorporates mixed waters from the Kuroshio Current and the SCS, and thus has higher thermohaline characteristics than local marine waters. Time series of eddy kinematic parameters show that the radii and shape of the LWE vary during propagation, and its eddy kinetic energy follows a normal distribution. In addition, we used the empirical orthogonal function (EOF) here to analyze seasonal characteristics of the LWE. The results suggest that the LWE generally forms in July, intensifies in August and September, separates from the coast of Luzon in October and propagates westward, and weakens in December and disappears in February. The LWE’s westward migration is approximately along 19°N latitude from northwest of Luzon to southeast of Hainan, with a mean speed of 6.6 cm/s.  相似文献   

16.
Historical hydrographic data across several sections in the South China Sea (SCS) and Taiwan Strait have been reconsidered. The year-around existence of the South China Sea Warm Current (SCSWC) along the shelf break off the Guangdong coast and the seemingly year-around southwestward current to the east of SCSWC are both evident in the data. The data also showed that the northward current in the Taiwan Strait seemed to be the extension of SCSWC. A barotropic numerical model is employed to explain some of the observed features. Reasonable simulation of the circulation in the northeast part of SCS has been found.  相似文献   

17.
A three-dimensional isopycnic-coordinate ocean model for the study of internal tides is presented. In this model, the ocean interior is viewed as a stack of isopycnic layers, each characterized by a constant density. The isopycnic coordinate performs well at tracking the depth variance of the thermocline, and is suitable for simulation of internal tides. This model consists of external and internal modes, and barotropic and baroclinic motions are calculated in the two modes, respectively. The capability of simulating internal tides was verified by comparing model results with an analytical solution. The model was then applied to the simulation of internal tides in the South China Sea (SCS) with the forcing of M2 and K1 tidal constituents. The results show that internal tides in the SCS are mainly generated in the Luzon Strait. The generated M2 internal tides propagate away in three different directions (branches). The branch with the widest tidal beam propagates eastward into the Pacific Ocean, the most energetic branch propagates westward toward Dongsha Island, and the least energetic branch propagates southwestward into the basin of the SCS. The generated K1 internal tides propagate in two different directions (branches). One branch propagates eastward into the Pacific Ocean, and the other branch propagates southwestward into the SCS basin. The steepening process of internal tides due to shoaling effects is described briefly. Meridionally integrated westward energy fluxes into the SCS are comparable to the meridionally integrated eastward energy fluxes into the Pacific Ocean.  相似文献   

18.
Using merged sea level anomaly and absolute geostrophic velocity products from satellite altimetry and Argos drifter data,we analyzed the reversal process of the South China Sea(SCS) western boundary current(SCSwbc) from a summer to winter pattern in 2011 and important oceanic phenomena during this process.Results show that the outbreak time of the northeast monsoon over the southern SCS lagged that over the northern SCS by about 1 month.During the SCS monsoon reversal period,the SCSwbc reversed rapidly into the winter pattern at the Guangdong continental slope in late September.Subsequently,the southward Vietnam coastal boundary current strengthened.However,the northward Natuna Current maintained a summer state until mid-October.Thus,the balance between the southward and northward currents was lost when they met,their junction moved gradually southward.However,a loop current formed southeast of Vietnam because the main stream of the Vietnam Offshore Current(VOC) remained near its original latitude.Meanwhile,the VOC and associated dipole circulation system strengthened.After midOctober,the northward Natuna Current began to weaken,the loop current finally shed,becoming a cool ring.The VOC and its associated dipole sub-basin circulation system also weakened gradually until it disappeared.  相似文献   

19.
We investigated the interaction between mesoscale eddies and the Kuroshio Current east of Taiwan,China,using a fine-resolution regional general circulation model.Mesoscale eddies are injected into a region east of Taiwan,China,according to the quasi-geostrophic theory of stratified fluids.Modeled eddies propagated westward at the velocity of the first baroclinic mode Rossby wave.When eddies collide with the Kuroshio Current east of Taiwan,China,the spatial structure and volume transport of the Kuroshio Current shows a significant variation.The upper 600 m of the anticyclonic eddy cannot cross the Kuroshio Current to reach the region west of the Kuroshio Current;rather,these waters flow northward along the eastern side of the Kuroshio Current.The upper water carried by the anticyclonic eddies cannot reach the shelf of the East China Sea(ECS).In contrast,the waters in the upper layer of the cyclonic eddy reach the western side of the Kuroshio Current and then flow northward.The dynamic mechanism analysis shows that the interaction between the Kuroshio Current and the cyclonic(anticyclonic) eddy decrease(increase)the horizontal potential vorticity(PV) gradient,or PV barrier,whereby the cyclonic(anticyclonic) eddy can(cannot) cross the Kuroshio Current.This study implies that the continental shelf could potentially be influenced by cyclonic eddies in the open ocean,which can transport heat and material from the upper open ocean acro s s the Kuroshio Current to the shelf waters.  相似文献   

20.
The sensitivity of the global atmospheric and oceanic response to sea surface temperature anomaly (SSTA) throughout the South China Sea (SCS) is investigated using the Fast Ocean-Atmosphere Model (FOAM). Forced by a warming SST, the experiment explicitly demonstrates that the responses of surface air temperature (SAT) and SST exhibit positive anomalous center over SCS and negative anomalous center over the Northern Pacific Ocean (NPO). The atmospheric response to the warm SST anomalies is characterized by a barotropical anomaly in middle-latitude, leading to a weak subtropical high in summer and a weak Aleutian low in winter. Accordingly, Indian monsoon and eastern Asian monsoon strengthen in summer but weaken in winter as a result of wind convergence owing to the warm SST. It is worth noting that the abnormal signals propagate poleward and eastward away in the form of Rossby Waves from the forcing region, which induces high pressure anomaly. Owing to action of the wind-driven circulation, an anomalous anti-cyclonic circulation is induced with a primary southward current in the upper ocean. An obvious cooling appears over the North Pacific, which can be explained by anomalous meridional cold advection and mixing as shown in the analysises of heat budget and other factors that affect SST.  相似文献   

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