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1.
E.
zsoy A. Hecht Ü. Ünlüata S. Brenner H.I. Sur J. Bishop M.A. Latif Z. Rozentraub T. Oguz 《Deep Sea Research Part II: Topical Studies in Oceanography》1993,40(6)
The Levantine Basin circulation derived from recent data consists of a series of sub-basin-scale to mesoscale eddies interconnected by jets. The basin-scale circulation is masked by eddy variability that modulates and modifies it on seasonal and interannual time scales. Long-term qualitative changes in the circulation are reflected in the bifurcation pattterns of ther mid-basin jets, relative strengths of eddies and the hydrographic properties at the core of these eddies. Confinement within the Basin geometry strongly influences the co-evolution of the circulation features.Surface measurements, satellite images and the mass field indicate an entire range of scales of dynamical features in the region. The complexity of the circulation is consistent with the basin-wide and mesoscale heterogeneity of the hydrographic properties. The interannual variability of LIW (Levantine Intermediate Water) formation in the region appears correlated with the changes in the circulation. Wintertime convective overturning of water masses reach intermediate depths and constitute a dominant mechanism of LIW formation, especially in anticyclonic eddies and along the coasts of the northern Levantine Basin. 相似文献
2.
根据珠江口外沿岸海域2006年夏季(7-8月)及冬季(2006年12月-2007年1月)航次的CTD调查资料,分析了调查海域夏季与冬季的温度、盐度分布,温度、盐度、密度跃层特征及其与上升流、中尺度涡旋和海流的关系.结果表明:1)夏季调查海域冲淡水扩展、上升流、中尺度涡等现象在温度、盐度分布中都有很明显的表征,并对跃层分布有显著的影响,形成了复杂的跃层类型;在冲淡水扩展的影响下,还形成了双跃层与障碍层现象.2)冬季海水混合剧烈,沿岸浅水区域跃层现象不明显,在陆坡深水区存在跃层现象. 相似文献
3.
The residual currents in Tokyo Bay during four seasons are calculated diagnostically from the observed water temperature, salinity and wind data collected by Unokiet al. (1980). The calculated residual currents, verified by the observed ones, show an obvious seasonal variable character. During spring, a clear anticlockwise circulation develops in the head region of the bay and a strong southwestward current flows in the upper layer along the eastern coast from the central part to the mouth of the bay. During summer, the anticlockwise circulation in the head region is maintained but the southwestward current along the eastern coast becomes weak. During autumn, the preceding anticlockwise circulation disappears but a clockwise circulation develops in the central part of the bay. During winter, the calculated residual current is similar to that during autumn. As a conclusion, the seasonal variation of residual current in Tokyo Bay can be attributed to the variation of the strength of two eddies. The first one is the anticlockwise circulation in the head region of the bay, which develops in spring and summer and disappears in autumn and winter. The second one is the clockwise circulation in the central part of the bay, which develops in autumn and winter, decreases in spring and nearly disappears in summer. 相似文献
4.
Intercomparison of three South China Sea circulation models 总被引：2，自引：1，他引：1
1IntroductionTheSouthChinaSeaisthelargesttropicalmarginaldeepsealocatingbetweenthewesternPacificOceanandtheeasternIndianOcean.AsapartofAsia-Australiamaritimecontinent,monsoonisaprimaryfactorforcingtheSouthChinaSeaCurrent(SCSC)variation.Drivenbynortheasterlymonsooninwinterandsouth-westerlymonsooninsummer,respectively,theSCSCbehavesacyclonicgyreandananticy-clonicgyre,correspondingly(Wyrtki,1961;Xuetal.,1982).Owingtotheshortageandexpen-sivenessofdirectobservationsintheSCS,fur-therunder… 相似文献
5.
Macrofauna Communities in the Eastern Mediterranean Deep Sea 总被引：1，自引：0，他引：1
Abstract. During two expeditions with RV ‘Meteor’ in summer 1993 and winter 1997/98 the structural and functional diversity of the benthic system of the highly oligotrophic eastern Mediterranean deep sea was investigated. The macrofauna communities were dominated by polychaetes even at the deepest stations. The fauna at shallow stations was dominated by surface deposit feeders, whereas subsurface deposit feeders and predators generally increased with depth. A high percentage of suspension‐feeding Porifera was found in the Levantine Basin. Mean abundance and number of taxa of both expeditions were significantly correlated to depth and distance to the nearest coast as well as to the total organic carbon (TOC) content in sediments. Numbers of taxa and abundance decreased generally with depth, although lowest numbers were not found at the deepest stations but in the extremely oligotrophic Levantine and Ierapetra Basin. Biomass measured during the second cruise was extremely low in the Ierapetra Basin and comparable to other extreme oligotrophic seas. The significant correlations found for TOC contents and macrofauna with distance to coast during both expeditions apparently reflect the role of hydrographically governed transport of organic matter produced in coastal regions into greater and extreme depths of the Mediterranean Sea. Seasonal differences in macrofauna communities due to seasonal differences in food supply were not found. However, recent large‐scale hydrographic changes (Eastern Mediterranean Transient, EMT) might change the oligotrophy and, thus, the structure of the benthic communities in the Eastern Mediterranean deep sea. 相似文献
6.
利用调查数据及遥感数据揭示了2013年南沙群岛海域温跃层的季节变化特征,温跃层上界深度平均值春、夏、冬季基本一致,介于45~47 m之间,秋季最大,达60 m;温跃层厚度平均值夏、秋、冬季基本一致,介于85~87 m之间,春季相对较小,为78 m。温跃层强度平均值春、夏、秋、冬季几乎一致,介于0.13~0.15℃/m之间。调查海域温跃层上界深度季节变化的形成机理为:春季西深东浅的原因是西部受净热通量较小、大风速、负的风应力旋度以及中南半岛东部外海的中尺度暖涡和反气旋环流共同作用,东部近岸海域净热通量高值、风速相对较小及风应力旋度引起的Ekman抽吸效应共同控制;夏季深度分布较均匀的原因是10°N以北风致涡动混合强但受Ekman抽吸影响,10°N以南风致涡动混合弱但风应力旋度为负值;秋季深度较其他季节平均加深15 m的原因是南沙群岛海域被暖涡占据,暖涡引起的反气旋式环流使得温跃层上界深度被海水辐聚下压;冬季正的风应力旋度产生的Ekman抽吸和冷涡引起的气旋式环流共同作用,使得温跃层上界深度较秋季平均抬升15 m。 相似文献
7.
A. Raghunadha Rao G. Nageswara Rao P. Sreenivas P. V. Hareesh Kumar 《Marine Geodesy》2013,36(3):319-333
Spatial current data were collected from South eastern Arabian Sea during July 2009 (summer monsoon) and December 2009 (winter monsoon) using the vessel mounted Acoustic Doppler Current Profiler (ADCP). During July 2009, observed ADCP currents were flowing southward along 75°E longitude with a complex pattern near the coast. During winter (December 2009), an anti-clockwise rotation of currents was observed in the study region, with its eastern arm along the southwest coast of India. The circulation pattern observed during the two seasons from ADCP measured data does not seem to follow any pattern described in climatology. To investigate this aspect, the geostrophic currents were computed utilizing the multi-mission altimeter sea surface height anomaly data for the corresponding months. The analysis of geostrophic currents indicates the presence of multiple eddies embedded in the Laccadive Low (LL) /Laccadive High (LH). Our present study shows that the meso-scale eddies embedded in the LL and LH play a significant role in deviating the observed circulation from climatology in this region. In addition, generating mechanisms of these eddies are addressed to substantiate our findings. The formation of these eddies is attributed to the local wind force during July 2009 and the enhanced baroclinic instability during December 2009. 相似文献
8.
The seasonal variation of water circulation in the Seto Inland Sea is investigated using a high resolution, three-dimensional
numerical ocean model. The model results are assessed by comparison with long-term mean surface current and hydrographic data.
The simulated model results are consistent with observations, showing a distinct summer and winter circulation patterns. In
summer the sea water is highly stratified in basin regions, while it is well mixed near the straits due to strong tidal mixing
there. During this period, a cold dome is formed in several basins, setting up stable cyclonic eddies. The cyclonic circulation
associated with the cold dome develops from May and disappears in autumn when the surface cooling starts. The experiment without
freshwater input shows that a basin-scale estuarine circulation coexists with cyclonic eddy in summer. The former becomes
dominant in autumn circulation after the cold dome disappears. In winter the water is vertically well mixed, and the winter
winds play a significant role in the circulation. The northwesterly winds induce upwind (downwind) currents over the deep
(shallow) water, forming a “double-gyre pattern” in the Suo-Nada, two cyclonic eddies in Hiuchi-Nada, and anticyclonic circulation
in Harima-Nada in vertically averaged current fields. 相似文献
9.
《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(11):2347-2372
The spatial and seasonal variability of nutrients and dissolved oxygen concentrations as well as the chemical characterization of the different water masses of the Southern Levantine Basin were determined in detail. In summer, the upper 150 m of the water body was stratified and the cross basin distribution of dissolved oxygen and nutrients was fairly constant. Surficial waters were saturated with dissolved oxygen, and a shallow oxygen maximum (oversaturated) was present at about 80 m depth. Oversaturation was attributed mainly to the physical process of rapid capping and trapping of oxygen in the Atlantic water (AW) mass, with only 28% of the excess oxygen originating from biological production. Nutrient concentrations were very low and showed an increase in the intermediate levels, coupled with a decrease in oxygen. The winter cross-section distribution showed an upper mixed layer of 100 m, with dissolved oxygen and nutrient concentrations fairly constant across the basin. The concentration of nitrate was higher than in summer, while phosphate was slightly lower and silicic acid similar. In winter, the influence of the physical features (gyres) could be detected up to the surface, and in summer they were detected by the chemical properties in the 150–600 m layer. In the transition layer between the Levantine intermediate water (LIW) and the deep water (DW) (400–700 m) there was a gradual decrease in dissolved oxygen and an increase in nutrient concentrations eastwards. The DW showed no seasonal variation, only spatial variability: dissolved oxygen decreased and silicic acid increased eastwards. No differences were found in nitrate and phosphate concentrations between the DW in the western and eastern provinces, indicating the oxidation of organic matter poor in N and P.N : P ratios in the upper water masses were seasonally dependent. The largest variation was found in the Levantine surface water (LSW), from an average of 52 in winter to 5 in summer. It is hypothesized that the gradual decrease from winter to summer values was due mainly to preferential atmospheric input of N in winter and P in summer, together with biological consumption and differential regeneration of N and P. In the DW, the N : P ratios were constant throughout the year (25.2±2.7, n=567), and higher than Redfield's ratio. It was speculated that the high N : P ratio in the DW was a result of oxidation of particulate organic matter deficient in P.The winter wet atmospheric input of N provided 12% of new N to the LSW. Average new production for the Southern Levantine Basin was estimated from the new N as 4.75 g C m−2 yr−1. The dry atmospheric contribution of P was estimated to significantly increase the P pool in the LSW. Dry deposition is not evenly distributed and occurs in episodic and localized events, which may have a large effect on productivity in the short periods when deposition occurs.There have been recently reported changes in the deep thermohaline circulation of the Eastern Mediterranean, with main contribution of the Aegean Sea as a source of DW. The data presented here can serve as a reference for assessing future changes in the chemical composition of the water masses in the Southern Levantine. 相似文献
10.
基于POM(Princeton Ocean Model)海洋模式,对南海不同深度环流的季节性变化进行了数值模拟研究。模拟结果表明:南海表层和上层环流受季风影响,在夏季西南季风驱动下,南海表层环流在南部呈现强反气旋式结构,在南海北部则是一个弱的气旋环流;在冬季东北季风驱动下,南海表层环流结构呈气旋式,并且明显加强了沿越南沿岸向南流动的西边界流;春季和秋季为南海季风的转换期,其对应的环流特征也处于冬季环流与夏季环流的过渡流型,流速与冬季和夏季相比较弱。南海200m层环流的季节变化与表层相似。在500与1 000m层,则出现许多处中尺度漩涡,流场也变得较为紊乱。 相似文献
11.
海浪混合参数化的渤海、黄海、东海水动力环境数值模拟 总被引：9，自引：2，他引：9
在浪-流耦合的概念下,对Princeton Ocean Model(POM)模式进行改进,增加特征波参数下的海浪混合作用,并把潮流和环流同时模拟,得到了渤海、黄海、东海典型的环流和水文特征,特别是夏季黄海的温跃层现象,夏季长江冲淡水扩展路径以及我国东部海域冬季和夏季典型环流等.研究表明,海浪的作用使海洋上层混合得更均匀,潮流的作用使海洋底层混合得更均匀,二者是温跃层形成的重要原因;考虑潮效应模拟流场,由于潮扩散和潮余流的作用,长江冲淡水路径与实际观测更为符合. 相似文献
12.
Repeated hydrographic casts, mooring time series and satellite sea surface temperature collected during the CANALES experiment (1996–98) are used to describe the thermohaline circulation in the Balearic Channels (western Mediterranean) and to analyze its variability. Mass transports are estimated by inverse calculations. The role played by each channel in the meridional water exchange is clarified: the Ibiza Channel funnels southward cool, saline, northern waters whereas the Mallorca Channel appears as the preferred route for the northward progression of warm, fresh, southern waters. A neat interannual trend is revealed by the continuous decrease of the amount of Western Mediterranean Intermediate Waters (WIW) brought by the Northern Current, reflecting the increase in temperature of the winter mixed layer in the northern Mediterranean that occurred each year between 1996 and 1998. A clear seasonal signal was also seen in the transport of the Northern Current which decreased from 1 to 1.4 Sv in winter to < 0.5 Sv in summer. The current intensified again in fall. A number of mesoscale eddies, from 20 to 70 km in size, most of them anticyclonic vortex eddies were brought by the unstable Northern Current, these eddies strongly perturbed the water exchange in the Ibiza Channel forcing retroflections of northern waters back to the north-east into the Balearic Current. These eddies either stayed stalled for several months in the Gulf of Valencia to the north of the channel, or were slowly funnelled southward through the channel narrows. A decreasing trend was observed in the mesoscale activity of the Northern Current between 1996 and 1998. Conversely, large, anticyclonic eddies, 150-km diameter, progressively invaded the Algerian Basin to the south of the channels in 1997–98 and forcing northward inflows (up to 0.75 Sv) of fresh and warm waters of Atlantic origin (AW) into the Mallorca Channel. The marked interannual differences observed in both northern and southern eddy activity may be linked to the interannual variability of the large scale thermohaline circulation. 相似文献
13.
This paper describes the water circulation in the Kuril Basin and its role in the formation and seasonal variation in intensity
of the large anticyclonic eddies which occur in the basin. Oceanographic data for the period June 1977 through June 1979 suggest
that these eddies develop in summer and decay in winter. In summer, the eddy development is associated with a deepening of
the isopycnals caused by the surface flow of the Soya Warm Current over the basin, and the deep advection of cold, less saline,
oxygen-rich water from Terpenia Bay and the eastern continental shelf of Sakhalin Island. In winter, the eddy decay is caused
by surface cooling and convective mixing downward of the warm, saline surface water, which causes the isopycnals to rise and
leads to an attenuation of the eddies. This combination of the summer influx of water into the region, and the fall and winter
cooling of the eddies leads to the annual variation in eddy intensity. 相似文献
14.
为研究帕里西维拉海盆区上层水体中悬浮体分布特征,对2003年冬季在该海区现场测得的上层水体悬浮体质量浓度数据进行详细分析。结果表明,调查期间研究区悬浮体质量浓度在水平上表现出西高东低的特征,垂向上的差异较小。现场大面站调查和同期卫星高度计数据显示,调查期间在研究区海域同时存在冷涡和暖涡活动,其中冷涡活动区位于研究区西部,暖涡活动区位于东部。分层分析表明,调查区中尺度涡活动对悬浮体分布有明显的控制效应:在冷涡活动区内,深层的富营养盐水体上涌,使冷涡内部的浮游生物量增多,导致冷涡活动区内的悬浮体质量浓度明显高于周围;在暖涡活动区内,因上层的寡营养盐水体下沉,使暖涡区的浮游生物量减少,导致悬浮体质量浓度明显低于周围。受洋流和中尺度涡活动的影响,调查海区西北部岛礁的物质供应也是导致研究区悬浮体分布呈现西高东低格局的重要因素。 相似文献
15.
Features of eddy kinetic energy and variations of upper circulation in the South China Sea 总被引：8，自引：3，他引：8
The features of eddy kinetic energy (EKE) and the variations of upper circulation in theSouth China Sea (SCS) are discussed in this paper using geostrophic currents estimated from Maps of Sea Level Anomalies of the TOPEX/Poseidon altimetry data. A high EKE center is identified in the southeast of Vietnam coast with the highest energy level 1 400 cm2 ·s~(-2) in both summer and autumn. This high EKE center is caused by the instability of the current axis leaving the coast of Vietnam in summer and the transition of seasonal circulation patterns in autumn. There exists another high EKE region in the northeastern SCS, southwest to Taiwan Island in winter. This high EKE region is generated from the eddy activities caused by the Kuroshio intrusion and accumulates more than one third of the annual EKE, which confirms that the eddies are most active in winter. The transition of upper circulation patterns is also evidenced by the directions of the major axises of velocity variance ellipses between 10°and 14.5°N 相似文献
16.
南海的季节环流─TOPEX/POSEIDON卫星测高应用研究 总被引：57，自引：8，他引：49
应用1992～1996年的TOPEX/POSEIDON卫星高度计遥感资料,研究了冬、夏季风强盛期多年平均的南海上层环流结构。研究结果表明,南海上层流结构呈明显的季节变化,在很大程度上受该海区冬、夏交替的季风支配。冬季总环流呈气旋型,并发育有两个次海盆尺度气旋型环流;夏季总环流大致呈反气旋型、但在南海东部18°N以南海域未见明显流系发育。研究还表明,南海环流的西向强化趋势明显,无论冬、夏在中南半岛沿岸和巽他陆架外缘均存在急流,其流向冬、夏相反,是南海上层环流中最强劲的一支。鉴于该海流的动力特征与海洋动力学中定义的漂流不同,有相当大的地转成分,建议称为“南海季风急流(South China Sea MonsoonJet)”.冬季南下的季风急流在南海南部受巽他陆架阻挡折向东北,沿加里曼丹岛和巴拉望岛外海有较强东北向流发育。夏季北上的季风急流在海南岛东南分为两支:北支沿陆架北上,似为传统意义上的南海暖流;南支沿18°N向东横穿南海后折向东北;二者之间(陆架坡折附近)为弱流区。两分支在汕头外海汇合后,南海暖流流速增强。就多年平均而言,黑潮只在冬季侵入南海东北部,并在南海北部诱生一个次海盆尺度的气旋型环流,这时南海暖流只出现在汕头以东海域.夏季南海北部完全受东北向流控制,未见黑潮入侵迹象.用卫星跟踪海面漂流浮标观测进行的对比验证表明,以上遥感分析结果与海上观测一致。 相似文献
17.
近年来的现场观测和理论研究发现, 次中尺度现象广泛存在于上层海洋, 其产生与锋生作用及混合层斜压不稳定存在密切联系。本文利用高分辨率的数值模拟结果并结合动力学及能量诊断分析, 对黑潮延伸体海域次中尺度过程的季节变化进行了探讨。探讨结果表明, 黑潮延伸体海域次中尺度过程具有冬季最强, 春季和秋季次之, 夏季最弱的显著季节变化特征。基于冬、夏季次中尺度能量源的诊断可以看到, 这些季节变化特征主要与上层海洋的斜压不稳定和锋生作用有关。冬季, 黑潮延伸体海域的中尺度能量较弱, 但次中尺度过程在季节尺度上表现最为活跃, 这主要与混合层斜压不稳定的作用有关; 夏季, 黑潮延伸体海域的混合层较浅, 次中尺度过程较弱, 但中尺度涡旋活跃, 中尺度流场变形引起的锋生作用对夏季次中尺度现象的产生具有重要影响。在次中尺度能量的季节变化方面, 冬季次中尺度过程从中尺度过程汲取能量的速率远高于夏季, 这是冬季次中尺度过程比夏季更为活跃的主要原因。本文研究结果有助于加深对黑潮延伸体海域次中尺度过程季节性变化及其动力机制的理解。 相似文献
18.
A new hypothesis about the surface circulation in the eastern basin of the mediterranean sea 总被引：3，自引：1，他引：3
In time, the circulation of the Atlantic Water (AW) in the eastern basin of the Mediterranean Sea has been described differently, according to two major representations. The historical one, which began with the scheme from Nielsen in 1912 and has been refined up to the 1980s, favours a counterclockwise circulation in the whole basin, with AW flowing in its southern part as a broad flow off Libya and Egypt (from the Ionian to the Levantine subbasins), then continuing along Middle-East and Turkey before flowing back westwards. The more recent one, issued in the 1990s, favours a clockwise circulation in the northern part of the Ionian continuing offshore across the basin from the Cretan to the central part of the Levantine as the so-called “Mid-Mediterranean Jet”. This jet is depicted then as splitting both clockwise in the southeastern part of the basin and counterclockwise off Turkey (where this representation agrees with the former). Because the recent representation cannot be considered as a refinement of the historical ones, we have been interested in understanding why a given data set available to everybody is interpreted in such different ways.In the Algerian subbasin, the combined use of satellite infrared images and a significant amount of in situ data sets (hydrology and both Eulerian and Lagrangian current measurements) allowed us to solve a similar controversy. Therefore, we examined the circulation features in the eastern basin, undertaking the detailed analysis of 1000 daily and weekly composite images spanning the period 1996–2000, and of monthly composite images available since 1985. Whenever in situ observations were available, we have confronted them with the satellite thermal signatures and have shown that both are consistent. This paper focuses on the overall (basin scale) results while the detailed ones are published in an other paper. The new scheme we propose is basically a refined version of the historical ones: the circulation of AW is counterclockwise in the whole eastern basin but it is more constrained alongslope than previously thought, and the broadening historically schematised appears to be due to intense mesoscale eddies mainly generated by the instability of this circulation. 相似文献
19.
J. G. Bruce 《Geo-Marine Letters》1995,15(3-4):185-194
A considerable amount of the Amazon River water that is discharged into the equatorial Atlantic is then advected northward along the shelf by the strong North Brazil Current (NBC). Being relatively fresh, this water remains in the near-surface layer and can serve as an excellent tracer for the complex and variable flow of the offshore mesoscale eddies. Both surface salinity observations and CZCS (Coastal Zone Color Scanner) imagery can be mapped to estimate the circulation patterns of the eddies. Presented here are two sets of XBT (expendable bathythermograph) sections that give the thermal structure of eddies off the Demerara Rise (6–9°N). They were occupied nearly contemporaneously with CZCS imagery obtained during October 1980 and November 1981. Several studies have shown from ship drift data, from CZCS observations, and from Geosat altimetry that, particularly during late summer and fall, the NBC is found to retroflect offshore to the east, supplying the North Equatorial Counter Current (NECC) and is associated with eddies along the coast. Good agreement is shown between the CZCS and a NAVOCEANO AXBT (airborne bathythermograph) survey during this period as well as observations of surface phytoplankton and geopotential anomaly from an earlier 1964 survey. Estimates of volume transport within the eddy structure indicate that at times the offshore retroflection during spring as well as autumn can amount to 10 × 106 m3 s–1. The pronounced eddy variability off South America is shown by comparing a number of past hydrographic surveys. These suggest that considerable spatial variability can occur as can seasonal changes in volume transport of the NBC and the associated eddy circulation. 相似文献
20.
On the basis of the results obtained by using the PRECIS regional climate model with high space resolution (25 km), we study
the mesoscale specific features of the atmospheric circulation in the Black-Sea region for a period of 30 yr. To separate
and trace the subsynoptic eddies, we use a method based on the Okubo–Weiss criterion. Several types of cyclonic eddies are
selected and described: winter Caucasian coastal eddies, summer Caucasian separated eddies, cyclonic eddies of the open sea,
and seldom quasitropical cyclones. For various types of eddies, we present the statistics of their lifetime and intensity
and the histograms of diurnal and seasonal cycles. 相似文献