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1.
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.  相似文献   

2.
《大气与海洋》2012,50(4):40-58
The hydrography, wind, Argos and Argo measurements in the areas surrounding Luzon Strait were collected. Based on the hydrographic data obtained during September 1994, the improved Princeton Ocean Model using a generalized topography-following coordinate system together with a modified inverse method was applied to study the circulation in September. Observations and the diagnostic simulation produce a consistent circulation pattern, and the main dynamical features can be summarized as follows. (1) The Kuroshio has two branches with the main Kuroshio existing above 800 m depth and the western part existing above 400 m depth. The western branch of the Kuroshio leaves the main current near 20.5°N, then flows northwestward through Luzon Strait and finally flows out of the northern boundary southwest of Taiwan, consistent with the trajectory of Argos drifters. (2) The non-linear term is important and cannot be neglected in the momentum equations in the northern part of Luzon Strait under the baroclinicity field. Using non-linear dynamics, the westward intrusion of the Kuroshio into the northern part of Luzon Strait is more curved than when using linear dynamics. However, the non-linear term is smaller and so negligible around Luzon Strait under the homogeneous density field. (3) In the area from 117°E to 119°E and from 20.2°N to 21.7°N, an anticyclonic eddy appears east of Dongsha Islands. (4) At depths above 400 m, the circulation is mainly dominated by the basin-scale cyclonic gyre. (5) In the computational domain west of 121°E, the circulation below 800 m is mainly dominated by the basin-scale anticyclonic gyre. (6) The South China Sea water flows eastward across Luzon Strait in the middle layers, then turns cyclonically, finally flowing northward into the region east of Taiwan Island, which is qualitatively in agreement with the trajectories of Argo floats at about 1000 m depth in the area east of 121°E.

RÉSUMÉ?[Traduit par la rédaction] Nous avons rassemblé l'hydrographie, le vent, les Argo et les mesures Argo dans les régions avoisinant le détroit de Luçon. Sur la base des données hydrographiques relevées durant le mois de septembre 1994, nous avons appliqué le modèle océanique amélioré de Princeton utilisant un système de coordonnées « suivant le terrain » généralisé de pair avec une méthode inverse modifiée pour étudier la circulation en septembre. Les observations et la simulation diagnostique produisent une configuration de circulation cohérente dont on peut résumer comme suit les principales caractéristiques dynamiques. (1) Le Kuroshio possède deux branches : le Kuroshio principal existant au-dessus d'une profondeur de 800 m et la partie ouest existant au-dessus d'une profondeur de 400 m. La branche ouest du Kuroshio quitte le courant principal aux environs de 20,5°N et se dirige vers le nord-ouest à travers le détroit de Luçon pour finalement franchir la limite nord du détroit au sud-ouest de Taïwan, ce qui correspond à la trajectoire des bouées dérivantes Argos. (2) Le terme non linéaire dans les équations est important et ne peut pas être considéré négligeable de quantité de mouvement dans la partie nord du détroit de Luçon dans le champ de baroclinité. Lorsqu'on utilise la dynamique non linéaire, l'intrusion vers l'ouest du Kuroshio dans la partie nord du détroit de Luçon est plus incurvée que lorsqu'on utilise la dynamique linéaire. Cependant, le terme non linéaire est plus petit et donc négligeable autour du détroit de Luçon dans le champ de densité homogène. (3) Dans la région allant de 117°E à 119°E et de 20,2°N à 21,7°N, un remous anticyclonique apparaît à l'est des îles Dongsha. (4) Aux profondeurs inférieures à 400 m, la circulation est principalement dominée par le gyre cyclonique à l’échelle du bassin. (5) Dans le domaine de calcul à l'ouest de 121°E, la circulation sous 800 m est principalement dominée par le gyre anticyclonique à l’échelle du bassin. (6) Les eaux de la mer de Chine méridionale s’écoulent vers l'est à travers le détroit de Luçon dans les couches intermédiaires, puis tournent de façon cyclonique pour finalement s’écouler vers le nord dans la région à l'est de l’île Taïwan, ce qui, qualitativement, s'accorde avec la trajectoire des flotteurs Argo à environ 1000 m de profondeur dans la région à l'est de 121°E.  相似文献   

3.
分析了一个1/10°的涡分辨率全球环流模式LICOM(LASG/IAP Climate system Ocean Model)对吕宋海峡附近海洋环流的模拟能力。结果表明,模拟的吕宋海峡附近上层环流及输运具有明显的季节变化特征,除6月是东向净流出外,其余月份均为西向流入,冬季流量最大。年平均流量在-3.76 Sv(1 Sv=106 m3/s),其中上层(600 m以上)流量起主要贡献,为-3.60 Sv,与目前已有的研究结果基本一致。南海通过6个海峡完成与外界的水交换,其中吕宋海峡和巴拉巴克海峡是大洋水进入南海的主要通道,其余海峡均以流出为主,流出量最大的是台湾海峡(1.99 Sv),其次是卡里玛塔海峡(1.03 Sv)。进一步分析表明,由季风引起的埃克曼输送量约占吕宋海峡流量的11%,而由季风引起的吕宋海峡压力梯度形成的西向的地转流对吕宋海峡的输运起支配作用。作为黑潮源头的太平洋北赤道流流量对吕宋海峡输运的季节变化也有一定影响。  相似文献   

4.
The dynamics of the seasonal surface circulation in the Philippine Archipelago (117°E–128°E, 0°N–14°N) are investigated using a high-resolution configuration of the Regional Ocean Modeling System (ROMS) for the period of January 2004–March 2008. Three experiments were performed to estimate the relative importance of local, remote and tidal forcing. On the annual mean, the circulation in the Sulu Sea shows inflow from the South China Sea at the Mindoro and Balabac Straits, outflow into the Sulawesi Sea at the Sibutu Passage, and cyclonic circulation in the southern basin. A strong jet with a maximum speed exceeding 100 cm s−1 forms in the northeast Sulu Sea where currents from the Mindoro and Tablas Straits converge. Within the Archipelago, strong westward currents in the Bohol Sea carry the surface water of the western Pacific (WP) from the Surigao Strait into the Sulu Sea via the Dipolog Strait. In the Sibuyan Sea, currents flow westward, which carry the surface water from the WP near the San Bernardino Strait into the Sulu Sea via the Tablas Strait.These surface currents exhibit strong variations or reversals from winter to summer. The cyclonic (anticyclonic) circulation during winter (summer) in the Sulu Sea and seasonally reversing currents within the Archipelago region during the peak of the winter (summer) monsoon result mainly from local wind forcing, while remote forcing dominates the current variations at the Mindoro Strait, western Sulu Sea and Sibutu passage before the monsoons reach their peaks. The temporal variations (with the mean removed), also referred to as anomalies, of volume transports in the upper 40 m at eight major Straits are caused predominantly by remote forcing, although local forcing can be large during sometime of a year. For example, at the Mindoro Strait, the correlation between the time series of transport anomalies due to total forcing (local, remote and tides) and that due only to the remote forcing is 0.81 above 95% significance, comparing to the correlation of 0.64 between the total and local forcing. Similarly, at the Sibutu Passage, the correlation is 0.96 for total versus remote effects, comparing to 0.53 for total versus local forcing. The standard deviations of transports from the total, remote and local effects are 0.59 Sv, 0.50 Sv, and 0.36 Sv, respectively, at the Mindoro Strait; and 1.21 Sv, 1.13 Sv, and 0.59 Sv at the Sibutu Passage. Nonlinear rectification of tides reduces the mean westward transports at the Surigao, San Bernardino and Dipolog Straits, and it also has non-negligible influence on the seasonal circulation in the Sulu Sea.  相似文献   

5.
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.  相似文献   

6.
By analyzing the results of a realistic ocean general circulation model (OGCM) and conducting a series of idealized OGCM experiments, the dynamics of the Kuroshio Current System is examined. In the realistic configuration, the Kuroshio Current System is successfully simulated when the horizontal resolution of OGCMs is increased from 1/2° to 1/10°. The difference between the two experiments shows a jet, the model’s Kuroshio Extension, and a pair of cyclonic and anticyclonic, “relative,” recirculation gyres (RRGs) on the northern and southern flanks of the jet. We call them recirculation gyres because they share some features with ordinary recirculation gyres in previous studies, and we add the adjective “relative” to emphasize that they may not be apparent in the total field. Similar zonal jet and RRGs are obtained also in the idealized model with a rectangular basin and a flat bottom with a horizontal resolution of 1/6°. The northern RRG is generated by the injection of high potential vorticity (PV) created in the viscous sublayer of the western boundary current, indicating the importance of a no-slip boundary condition. Since there is no streamline with such high PV in the Sverdrup interior, the eastward current in the northern RRG region has to lose its PV anomaly by viscosity before connecting to the interior. In the setup stage this injection of high PV is carried out by many eddies generated from the instability of the western boundary current. This high PV generates the northern RRG, which induces the separation of the western boundary current and the formation of the zonal jet. In the equilibrium state, the anomalous high PV values created in the viscous sublayer are carried eastward in the northern flank of the zonal jet. The southern RRG is due to the classical Rhines–Young mechanism, where low PV values are advected northward within the western boundary inertial sublayer, and closed, PV-conserving streamlines form to the south of the Kuroshio Extension, allowing slow homogenization of the low PV anomalies. The westward-flowing southern branch of this southern RRG stabilizes the inertial western boundary current and prevents its separation in the northern half of the Sverdrup subtropical gyre, where the western boundary current is unstable without the stabilizing effect of the southern RRG. Therefore, in the equilibrium state, the southern RRG should be located just to the north of the center of the Sverdrup subtropical gyre, which is defined as the latitude of the Sverdrup streamfunction maximum. The zonal jet (the Kuroshio Extension) and the northern RRG gyre are formed to the north of the southern RRG. This is our central result. This hypothesis is confirmed by a series of sensitivity experiments where the location of the center of the Sverdrup subtropical gyre is changed without changing the boundaries of the subtropical gyre. The locations of the zonal jets in the observed Kuroshio Current System and Gulf Stream are consistent as well. Sensitivities of the model Kuroshio Current System are also discussed with regard to the horizontal viscosity, strength of the wind stress, and coastline.  相似文献   

7.
《大气与海洋》2012,50(4):27-39
On the basis of Acoustic Doppler Current Profiler (ADCP) measurements of current and hydrographic data obtained in October 2008, a diagnostic model of ocean circulation with a modified inverse method is used to study the circulation in Luzon Strait. Satellite-based geostrophic velocity calculated from the merged absolute dynamic topography is also used and compared with the in situ data. The analyses reveal that during the period of observations there were two branches of the Kuroshio current, and the maximum velocity of the current reached 175 cm s?1 at the surface. The main stream of the Kuroshio was located at 122°10′E to 122°40′E near the southern boundary of the study region and confined to the upper 700 m, while its western branch was located at 121°00′E to 121°35′E and confined to the upper 400 m. The Kuroshio water intruded into the South China Sea through the northern boundary of the study region east of 120°45′E. At 1000 m depth, the flow was dominated by southwestward or westward flow in the area north of 20°30′N, while the flow was mostly southeastward in the area south of 20°30′N. A cyclonic eddy was identified in the region east of Luzon Strait. At 1500 m depth, cyclonic eddies were seen on both sides of Luzon Strait. The volume transport across the longitudinal section 120°45′E between about 20.00°N and 21.20°N south of Taiwan during the period of observations was about 4?×?106 m3 s?1. One Argo float was tracked as it moved across Luzon Strait, reflecting the westward flow at both the surface and 1000 m depth.

RÉSUMÉ?[Traduit par la rédaction] En partant des mesures de courant par profileur de courant à effet Dopler (ADCP) et des données hydrographiques recueillies en octobre 2008, nous étudions la circulation dans le détroit de Luçon en nous servant d'un modèle diagnostique de la circulation de l'océan combiné à une méthode inverse modifiée. Nous nous servons également de la vélocité géostrophique mesurée par satellite, calculée à partir de la topographie dynamique absolue totale, pour la comparer avec les données in situ. Les analyses révèlent que pendant la période d'observation, il y avait deux ramifications du Kuroshio et que la vélocité maximale du courant a atteint 175 cm s?1 à la surface. La principale ramification du Kuroshio était située entre 122°10′E et 122°40′E à proximité de la limite sud de la région à l'étude et elle était confinée aux 700 premiers mètres; sa ramification ouest était située entre 121°00′E et 121°35′E et elle était confinée aux 400 premiers mètres. Le Kuroshio se déversait dans la mer de Chine occidentale en traversant la limite nord de la région à l'étude à l'est de 120°45′E. À 1000 m de profondeur, le courant s'écoulait essentiellement en direction sud-ouest ou ouest dans le secteur au nord de 20°30′N, et en direction sud-est dans la région au sud de 20°30′N. Nous avons identifié un tourbillon cyclonique dans la région à l'est du détroit de Luçon. Nous avons relevé des tourbillons cycloniques à une profondeur de 1500 m de part et d'autre du détroit de Luçon. Le transport volumique dans le profil longitudinal à 120°45′E entre 20.00° N et 21.20° N environ au sud de Taïwan pendant la période d'observation a atteint environ 4?×?106 m3 s?1. Nous avons suivi une bouée Argo dérivant au gré du courant dans le détroit de Luçon, ce qui a permis d’établir qu'il s'écoulait en direction ouest à la surface et à une profondeur de 1000 m.  相似文献   

8.
Response of the Kuroshio Current to Eddies in the Luzon Strait   总被引：1，自引：0，他引：1       下载免费PDF全文
The impact of eddies on the Kuroshio Current in the Luzon Strait (LS) area is investigated by using the sea surface height anomaly (SSHA) satellite observation data and the sea surface height (SSH) assimilation data. The influence of the eddies on the mean current depends upon the type of eddies and their relative position. The mean current is enhanced (weakened) as the cyclonic (anticyclonic) eddy becomes slightly far from it, whereas it is weakened (enhanced) as the cyclonic (anticyclonic) eddy moves near or within the position of the mean current; this is explained as the eddy-induced meridional velocity and geostrophic flow relationship. The anticyclonic (cyclonic) eddy can increase (decrease) the mean meridional flow due to superimposition of the eddy-induced meridional flow when the eddy is within the region of the mean current. However, when the eddy is slightly far from the mean current region, the anticyclonic (cyclonic) eddy tends to decrease (increase) the zonal gradient of the SSH, which thus results in weakening (strengthening) of the mean current in the LS region.  相似文献   

9.
A Note on the South China Sea Shallow Interocean Circulation   总被引：14，自引：1，他引：14  
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…  相似文献   

10.
A study of the circulation in the northern South China Sea （SCS） is carried out with the aid of a three-dimensional, high-resolution regional ocean model. One control and two sensitivity experiments are performed to qualitatively investigate the effects of surface wind forcing, Kuroshio intrusion, and bottom topographic influence on the circulation in the northern SCS. The model results show that a branch of the Kuroshio in the upper layer can intrude into the SCS and have direct influence on the circulation over the continental shelf break in the northern SCS. There are strong southward pressure gradients along a zonal belt largely seaward of the continental slope. The pressure gradients are opposite in the southern and northern parts of the Luzon Strait, indicating inflow and outflow through the strait, respectively. The sensitivity experiments suggest that the Kuroshio intrusion is responsible for generating the imposed pressure head along the shelf break and has no obvious seasonal variations. The lateral forcing through the Luzon Strait and Taiwan Strait can induce the southwestward slope current and the northeastward SCS Warm Current in the northern SCS. Without the lateral forcing, there is the continental slope. The wind forcing mainly causes the The wind-induced water pile-up results in the southward no high-pressure-gradient zonal belt seaward of seasonal variation of the circulation in the SCS. high pressure gradient along the northwestern boundary of the basin. Without the blocking of the plateau around Dongsha Islands, the intruded Kuroshio tends to extend northwest and the SCS branch of the Kuroshio becomes wider and stronger. The analyses presented here are qualitative in nature but should lead to a better understanding of the oceanic responses in the northern SCS to these external influence factors.  相似文献   

11.
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.  相似文献   

12.
The Florida Current flows through the Straits of Florida, which starts as a zonal channel and turns to become a meridional channel. The spatial structure of the Florida Current and its transport, potential vorticity, and related dynamical properties are investigated using a three-dimensional, baroclinic, primitive equation model with a mesoscale-admitting (5.6 km) horizontal resolution and 25 vertical (sigma: terrain-following) levels. At 83°W, the Florida Current fills only a portion of the channel; however, due to the interaction with the shoaling bottom topography (from a maximum depth of over 2000 m at 83°W to less than 800 m at 27°N) and the narrowing Straits of Florida (from a maximum width of about 170 km at 83°W to about 110 km at 27°N), the Florida Current fills the entire channel at 27°N, and the potential vorticity distribution is altered. The specified transport of 28.6 Sverdrup (1 Sv = 106 m3 s−1) from the Loop Current at the western boundary and the inflow from the Old Bahama Channel of 1.9 Sv converge into the meridional channel. With an additional inflow of 1.2 Sv from the Northwest Providence Channel, the simulated total transport of 31.8 Sv at 27°N is comparable to the STACS (Subtropical Atlantic Climate Studies) mean transport of 31.7 Sv. Both vertically and laterally integrated subsectional transports are examined at transects 83°W, 82°W, 81°W, 25°N, 26°N, and 27°N. The potential vorticity increases (decreases) on the cyclonic (anticyclonic) side of the Florida Current at 27°N compared to 83°W. The downstream variation of static stability, relative vorticity, and Froude number is also examined. While the vertical shear is strong only on the northern side at 83°W it is comparable on the both western and eastern sides downstream at 27°N, reaching to the bottom of the meridional channel. Large values of the Froude number exist only in the upper 300 m of the zonal channel, but they reach to the bottom of the meridional channel.  相似文献   

13.
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 ...  相似文献   

14.
南海夏季海流的数值模拟   总被引：3，自引：0，他引：3  
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。  相似文献   

15.
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.  相似文献   

16.
Summary The Gulf of Mexico (GOM) circulation is simulated using the DieCAST ocean model, with a horizontal resolution of 1/12° and 20 vertical layers. The results compare well with observations of both large and small scale features, including Loop Current frontal occlusions associated with frontal eddies. The simulation is carried out without any data assimilation. The frontal eddies tend to be spaced at about 90° intervals around the Loop Current, leading to a Loop Current head shaped like a square with rounded corners. The pattern rotates as the eddies circle the Loop, and frontal eddies elongate as they squeeze through the Florida Strait. Major warm core eddies separate regularly from the Loop Current and propagate to the western GOM. Old warm core eddies in the western Gulf dissipate through bottom drag effects, which also generate cyclonic parasitic eddies. Newly arrived warm core eddies merge with old ones in the western GOM. Recently separated elongated Loop Current eddies can rotate and reattach temporarily to the Loop Current. The barotropic flow component develops eddies between the main separated warm core eddy and the Loop Current due to eastward dispersion, as the main eddy itself propagates westward into the Gulf.With 10 Figures  相似文献   

17.
The Antarctic Circumpolar Current (ACC) is composed of three major fronts: the Sub-Antarctic Front (SAF), the Polar Front (PF), the Southern ACC Front (SACCF). The locations of these fronts are variable. The PF can shift away from its historical (mean) location by as much as 100 km. The transport of the ACC in Drake Passage varies from its mean (134 Sv) by as much as 60 Sv. A regional numerical circulation model is used to study frontal variability in Drake Passage as affected by a range of volume transports (from 95 Sv to 155 Sv with an interval of 10 Sv). Large transport shifts the fronts northward while the smaller transport causes a southward shift. The mean shifting distance of the PF from the historical mean location is minimum with 135 Sv transport. The SAF and the SACCF are confined by northern and southern walls, respectively, while the PF is loosely controlled by the topography. Due to impact of the eddies and meanders on the PF at several regions in Drake Passage, the PF may move northward to join the SAF or move southward to combine with the SACCF, especially in central Scotia Sea. The SAF and PF are more stable with higher transport. The SAF behaves as a narrow, strong frontal jet with large transport while displaying meanders with smaller transport. In the model simulations, the Ertel Potential Vorticity (EPV) is strongly correlated with the volume transport stream function. EPV at depths between 1000 and 2500 m is correlated with the transport stream function with a coefficient above 0.9. Near the bottom, the correlation is about 0.6 due to the disruptive influence of bottom topography. Within 750 m of the surface, the correlation is much reduced due to the effect of K-Profile Parameterization (KPP) mixing and eddy mixing.  相似文献   

18.
A legacy seismic section across the Luzon Strait was reprocessed using the pre-stack depth migration method to reveal thermohaline structures in the water column. Distinct finescale and mesoscale features can be seen from the seismic image. Vertically, reflective patterns are associated with three water layers: upper layer, intermediate layer, and deep layer. The upper layer can be divided into three areas by two opposing weak-to-transparent zones from west to east with individual thicknesses: ～400, 550, and 700 m. They are interpreted as the South China Sea upper water, the Kuroshio water, and the Pacific upper water, respectively, separated by two Kuroshio frontal zones. Internal waves are ubiquitous in the Kuroshio water fluctuating in different amplitudes and wavelengths laterally. The finestructure shows the western Kuroshio front zone is composed of three subparallel blanking zones with an average eastward dipping angle of 2.3°. They are regarded as the well-mixed frontal interfaces developed in and along a multi-frontal frontal zone. The transparent reflection of the intermediate water above the Hengchun is suggestive of a well-mixed layer by the near-bottom turbulence. In the Pacific intermediate water near the eastern mouth of the Bashi Channel, there is an inverted crescent-shaped structure, which is likely associated with the intrusion of the South China Sea intermediate water through the Bashi Channel. These imaged features are consistent with the observed oceanographic phenomena in the region.  相似文献   

19.
中国南海夏季风强、弱年多尺度相互作用能量学特征   总被引：1，自引：0，他引：1  
杨悦  徐邦琪  何金海 《气象学报》2016,74(4):556-571
中国南海夏季风为东亚季风的主要系统之一,其具有多重尺度特征,除季节平均环流场外,低频（季节内振荡）和高频（天气尺度）扰动也十分活跃,各尺度系统存在明显的年际变化。该研究使用ERA-Interim和NCEP/NCAR两套再分析资料,从季风平均动能（MKE）诊断的角度出发,探讨了1979-2010年中国南海夏季风环流年际变化的能量来源及其和扰动场的相互作用过程。结果表明:中国南海夏季风对流活跃年份,中国南海南部（12°N以南）及中南半岛一带为季风平均动能显著增强区,此与南亚季风区西风急流的增强并向东延伸有关;中国南海北部（12°N以北）及西太平洋为气旋性环流盘踞,季风槽加深。中国南海南部季风平均动能增强的能量源自于扰动动量通量与平均环流的相互作用,强季风年,平均环流失去较少的动能给扰动场（亦即平均环流保留较多的动能）。通过进一步探讨高频（<10 d）及低频（10-90 d）扰动场与平均环流不同分量的（散度、涡度、风垂直切变）相互作用过程,发现季风平均动能的增长主要来自于<10 d扰动与季风平均散度和涡度的相互作用。中国南海北部季风槽区季风平均动能的维持来自于大气热源和平均上升运动的相互作用,但同时有较多的季风平均动能向扰动动能转换,有利于扰动的成长。因此,强季风年,中国南海北部热带气旋生成数目增多,夏季北传的季节内振荡也增强,导致中国南部沿海及华南地区出现较多的灾害天气。   相似文献   

20.
Mesoscale resolution ocean general circulation model (EGCM) experiments have been carried out under a variety of different model physical assumptions, and the different model systems often produce very different deep mean flow fields. The flat bottom, rectangular basin experiments exhibit two distinct types of deep mean flow, which are here called “corotating” and “counterrotating”. Counterrotating deep flow, in which two adjacent deep gyres, with circulation of opposite senses, underlie the upper ocean eastward jet and its recirculation, has been found only in models with adiabetic two-layer model physics. None of the more complex model systems exhibit counterrotating deep flows; this type of flow is apparently restricted to a particular range of forcing/dissipation parameter space and/or particular model physical assumptions.Since the deep flow in these EGCM systems is generally weak, geostrophic dynamics provides the basic deep flow interior balance and the mean vertical velocity field, through the lower layer vorticity equation, largely determines the deep interior flow. The dynamical constraints on the mean vertical velocity field introduced by different model physical equations are reviewed and the adiabatic quasi-geostrophic (QG) two-layer model system is shown to be strongly constrained in several respects. In particular, the idea that eddy and mean heat flux divergence (or “layer thickness flux divergence”) drive the mean vertical velocity does not generalize to more complicated dynamical systems in which there is the possibility of altering the mean vertical density profile and/or in which the horizontal flow can be divergent. As a consequence of the constraints, there can be no basin net vorticity input to the lower layer via vortex stretching in the QG system.Because of the adiabatic QG constraints and the particular parametric regime in which the published adiabatic QG EGCM experiments exist, a very plausible explanation can be found for the existence of the deep cyclonic circulation of the model subtropical gyre. It is this cyclonic circulation that causes these deep flows to differ so dramatically from those of the more physically complex model systems. Because all the published adiabatic QG experiments that have non-trivial deep flows exhibit the counterrotating behavior, and because available ocean data do not support the existence of such a gyre in the North Atlantic, it seems important to thoroughly understand the reasons for the existence or absence of the deep cyclonic circulations. If they are an invitable feature of adiabatic QG systems, these models may need to be treated with caution as tools for understanding the mean ocean circulation.  相似文献   

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