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1.
The Gulf Stream system has been numerically simulated with relatively high resolution and realistic forcing. The surface fluxes
of the simulation were obtained from archives of calculations from the Eta-29 km model which is an National Center for Environment
Prediction (NCEP) operational atmospheric prediction model; synoptic fields are available every 3 hour. A comparison between
experiments with and without surface fluxes shows that the effect of the surface wind stress and heat fluxes on the Gulf Stream
path and separation is closely related to the intensification of deep circulations in the northern region. Additionally, the
separation of the Gulf Stream and the downslope movement of the Deep Western Boundary Current (DWBC) are reproduced in the
model results. The model DWBC crosses under the Gulf Stream southeast of Cape Hatteras and then feeds the deep cyclonic recirculation
east of the Bahamas. The model successfully reproduces the cross-sectional vertical structures of the Gulf Stream, such as
the asymmetry of the velocity profile, and this structure is sustained along the downstream axis. The distribution of Root
Mean Square (RMS) elevation anomaly of the model shows that the eddy activity of the Gulf Stream is realistically reproduced
by the model physics. The entrainment of the upper layer slope current into the Gulf Stream occurs near cross-over; the converging
cross-stream flow is nearly barotropic.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
Peter Hamilton 《Progress in Oceanography》1987,19(3-4)
The structure of the current and temperature fields along 30°N over the mid-shelf and western Blake Plateau in the South Atlantic Bight has been investigated by combining two moored instrument experiments in the summer of 1981. The shelf moorings were part of the second Georgia Bight Experiment (GABEX-II) and the Gulf Stream mooring data on the Blake Plateau have been described by LEE and WADDELL (1983). Empirical Orthogonal Functions (EOF) in the frequency domain are used to extract shelf and Gulf Stream coherent current and temperature fluctuations in the two- to 14-day period band. Three modes are found, of which the first two are interpreted as Gulf Stream meander and frontal eddy circulations. The difference between them is chiefly in the shelf motions; the first mode is primarily restricted to the shelf edge, whereas the second mode penetrates to the 40m isobath. The third mode dominates at mid-shelf and is the only mode that shows strong coherence with the windstress and local sea-level fluctuations. The relationship of the modes to the occurrence of mid- and inner-shelf cold sub-surface intrusions, generated by shelf-edge Gulf Stream frontal eddies, is examined. All three modes are found to play a role in the initiation, growth and decay of these structures. 相似文献
3.
J.J. Simpson 《Progress in Oceanography》1984,13(1):71-93
From January 9 to 17, 1981, detailed physical, chemical and biological measurements were made through the historical surface signature (Berstein, Breaker and Whritner, 1977; Burkov and Pavlova, 1980; Simpson, 1982) of a warm-core eddy in the California Current System. The data show a three-layer system: surface layer to 75 m, intermediate cold-core region to about 200 m, and the physically dominant subsurface warm-core eddy to about 1400 m. The chemical structure simultaneously possesses characteristics of both warm- and cold-core eddies. This structure results from a complex interplay among non-local eddy generation processes at the time the three-layer system was formed and a continuous set of interactions within the three-layer system, both inshore (cold) and offshore (warm) waters of the California Current and coastal and local biological processes (e.g. this California Current System eddy is an isolated structure like some Gulf Stream rings). The dominant biological/chemical process in the euphotic zone is phytoplankton photosynthesis; photosynthetic alteration of the chemical structure below 100 m is much reduced. The effects of heterotrophic activity on the deeper-lying chemical structure, however are not as significant as those of autotrophs on the chemical structure of the euphotic zone. Hence, below 100 m, the distribution and structure of chemical properties is controlled primarily by physical processes. The continuous set of interactions of the three-layer system with coastal and oceanic waters of the California Current make this offshore eddy in the California Current System fundamentally different chemically and biologically from cold-core Gulf Stream rings and rather similar to some of the warm-core eddies found in the East Australian Current. 相似文献
4.
两个西边界流延伸体区域中尺度涡统计特征分析 总被引：3，自引：2，他引：1
黑潮和湾流是世界大洋中最典型的两支西边界流，黑潮延伸体（Kuroshio Extention，KE）和湾流延伸体（Gulf Stream Extention，GSE）区域中尺度涡活动十分活跃。本文综合利用卫星高度计资料和Argo浮标资料，对KE和GSE区域中尺度涡的表层特征及其对温盐影响进行了统计研究和对比分析。结果表明:黑潮和湾流主轴附近为涡旋频率的高值区，主轴南北两侧分别以气旋涡和反气旋涡数量占多，主轴附近的涡旋强度明显大于其他区域；两个区域的涡旋以西向移动为主，气旋涡和反气旋涡都具有向南（赤道）偏离的趋势；两个区域的涡旋数量都以夏、秋季较多，涡旋强度都在春、夏季较大，且GSE区域涡旋强度明显大于KE区域；气旋涡（反气旋涡）引起内部明显的温度负（正）异常，KE区域气旋涡（反气旋涡）内部呈"负-正"（"正-负"）上下层相反的盐度异常分布，GSE区域气旋涡（反气旋涡）在各层呈现较为一致的盐度负（正）异常；两个区域中尺度涡对温盐场的平均影响深度可达1 000×104 Pa以上。 相似文献
5.
Analysis of measurements from two long-term moored arrays in and near the Gulf Stream suggests a simple parameterization of eddy spatial covariance statistics: a parameterization that can be referred to as “quasi-homogeneous and isotropic”. Taking the normalized covariance function (i.e. the correlation function) for streamfunction to be homogeneous and isotropic and assuming motions to be horizontally nondivergent and hydrostatic permit the velocity and temperature covariances to be derived from the streamfunction covariance. Statistical tests indicate that deviations from these assumptions are indistinguishable from Gaussian random noise. The spatial correlation function used in Gaussian with a decay scale of about 140 km, which is only weakly depth dependent. A simple form is also suggested for the vertical lag dependence. This parameterization permits calculation of derived quantities such as the eddy vorticity flux divergence which is discussed in the context of the mean potential vorticity balances for the depth integrated circulation and for the subthermocline layer. The divergence of the relative vorticity flux is found capable of driving two counter-rotating gyres of strength 30–40 Sv on either side of the Stream, as are observed. The “thickness flux” dominates the lower layer eddy potential vorticity flux and is of the correct sign to make the recirculation more barotropic. The lower layer eddy forcing is weak and the gyres exist in a region of nearly uniform mean potential vorticity. 相似文献
6.
As described by [Csanady, G.T., Hamilton, P., 1988. Circulation of slope water. Continental Shelf Research 8, 565–624], the flow regime over the slope of the southern Middle Atlantic Bight (MAB) includes a current reversal in which southwestward flow over the upper and middle slope becomes entrained in the northeastward current adjacent to the Gulf Stream. In this paper we use satellite-derived data to quantify how lateral motions of the Gulf Stream impact this current system. In our analysis, the Gulf Stream’s thermal front is delineated using a two-year time series of sea surface temperature derived from NOAA/AVHRR satellite data. Lateral motions of the Gulf Stream are represented in terms of temporal variations of the area, east of 73°W, between the Gulf Stream thermal front and the shelf edge. Variations of slope water flow within this area are represented by anomalies of geostrophic velocity as derived from the time series of the sea level anomaly determined from TOPEX/POSEIDON satellite altimeter data. A strong statistical relationship is found between Gulf Stream displacements and parabathic flow over the continental slope. It is such that the southwestward flow over the slope is accelerated when the Gulf Stream is relatively far from the shelf edge, and is decelerated (and perhaps even reversed) when the Gulf Stream is close to the shelf edge. This relationship between Gulf Stream displacements and parabathic flow is also observed in numerical simulations produced by the Miami Isopycnic Coordinate Model. In qualitative terms, it is consistent with the notion that when the Gulf Stream is closer to the 200-m isobath, it is capable of entraining a larger fraction of shelf water masses. Alternatively, when the Gulf Stream is far from the shelf-break, more water is advected into the MAB slope region from the northeast. Analysis of the diabathic flow indicates that much of the cross-slope transport by which the southwestward flow entering the study region is transferred to the northeastward flow exiting the region occurs in a narrow band roughly centered at 36.75°N, order 150 km north of Cape Hatteras. This transport, and thus the cyclonic circulation of the southern MAB, strengthens when the Gulf Stream is relatively close to the shelf edge, and weakens when the Gulf Stream is far from the shelf edge. 相似文献
7.
The distributions of iodide, iodate and total iodine were determined along a transect from the Sargasso Sea and across the Gulf Stream to the continental shelf of the South Atlantic Bight during November 1990. The western boundary of the Gulf Stream at the outer shelf-upper slope was characterized by steeply sloping isotherms and isopleths of iodide and iodate, resulting from a dome of cold water that was rich in iodate and nearly devoid of iodide at the slope. Both the mid and the inner shelf were relatively well mixed vertically. The concentration of iodate in the surface waters decreased shoreward from >0.3 μM in the Sargasso Sea/Gulf Stream/outer shelf, to 0.29 μM in the midshelf, 0.19 μM in the outer-inner shelf and 0.11 /IM in the inner-inner shelf. Concomitantly, the concentration of iodide increased from <161 nM to 175 nM, 257 nM and 300 nM. The concentration changes were more abrupt in the inner-inner shelf within about 30 km from the shore. There was no evidence of significant concentrations of organic iodine. These distributions of iodide and iodate suggest that the South Atlantic Bight may act as a geochemical processor of dissolved iodine. Iodate is added to the shelf during topographically induced upwelling and frontal exchange with the Gulf Stream. In the shelf waters, iodate is reduced to iodide in situ. Iodide is exported from the shelf to the Gulf Stream which may eventually further transport it to the ocean interior. A ☐ model calculation suggests that 28% and 43% of the iodate added to the Bight and the inner shelf, respectively, are converted to another form in these waters, almost all of which is iodide. About a third of the reduction of iodate to iodide in the Bight occurs in the inner shelf. Thus, the inner shelf may be the most geochemically active zone within the Bight. The residence times of iodide relative to its production and that of iodate relative to its removal are 3.1 and 3.6 months in the Bight and 0.9 and 1.8 months in the inner shelf. 相似文献
8.
9.
From January 9 to 17, 1981, detailed observations of the horizontal and vertical structure beneath one of the quasi-permanent semi-stationary mesoscale offshore eddy signatures in the California Current System (CCS) discussed by Bernstein, Breaker and Whritner (1977), Burkov and Pavlova (1980), and Simpson (1982) were made. The vertical sections of temperature and density show the presence of three-layer system. A subsurface warm-core eddy, whose diameter is about 150 km at the 7°C isotherm, is the dominant feature. A warm surface layer, which extends to a depth of 75 m, lies over the eddy. Between the warm surface layer and the subsurface warm-core eddy, there is a cold-core region which extends to a depth of about 200 m. There is a high degree of symmetry about the vertical axis of rotation. Vertical sections of salinity and dissolved oxygen are entirely different from sections of temperature and density. Diagrams of water mass characteristics confirm that the core of the eddy, found between 250–600 m, consists of inshore water from the California Undercurrent (CU). Below about 700 m, local waters from the Deep Poleward Flow (DPF) have been incorporated into the eddy. The observed distributions of properties (T, S, δθ, O2) are inconsistent with a single, local generation process for the eddy system. Radial distributions of angular velocity, normalized gradient velocity and relative vorticity support the use of a Gaussian radial height field as an initial condition in eddy models. Possible reasons why CCS eddies may differ dynamically from Gulf Stream rings are given in the text. At the time the observations were made, the system as a whole was in near geostrophic balance. Local geostrophic balance, however, cannot explain the observed distribution of properties and structure. The observed symmetry in the structure of the eddy system, chemical evidence (Simpson, 1984), biological distributions (Haury, 1984) and satellite images of the CC (Koblinsky, Simpson and Dickey, 1984) suggest that lateral entrainment of warm (oceanic) and cold (coastal) water into the upper two layers of the three-layer system by the subsurface eddy is a likely generation mechanism for the cold-core region. The coastal origin of the frontal structure along the northeastern quadrant and the oceanic origin of the frontal structure along the southwestern quadrant of the eddy system further support lateral entrainment as a generation mechanism for the cold core. This entrainment makes the CCS eddy system different from cold-core rings in the Gulf Stream and rather similar to some warm-core eddies found in the East Australian Current. The presence of CU water in the core of this eddy raises the question of how CU water was transported from the continental slope. Eddy generation mechanisms, other than baroclinic instability of the CC, may be required to explain the distribution, persistence, and core composition of offshore mesoscale eddies in the CCS. There is evidence that barotropic, in addition to baroclinic, processes may be important. 相似文献
10.
Terrence M. Joyce 《Journal of Oceanography》2012,68(1):45-52
In this report, eighteen-degree water (EDW) formation will be discussed, with emphasis on advances in understanding emerging
within the past decade. In particular, a recently completed field study of EDW (CLIMODE) is suggesting that EDW formation
within a given winter can have at least two different dominant physics and distinct locations: one type formed in the northern
Sargasso Sea, largely away from the strong flows of the Gulf Stream where 1D physics may apply, and a second type formed along
the southern flank of the Gulf Stream, in a region where the background vorticity of the flow and cross-frontal mixing play
key roles in the convective formation process. 相似文献
11.
《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(1-2):139-164
The principal meeting point of the subtropical and subpolar gyres of the North Atlantic is at the Tail of the Grand Banks where the two western boundary currents, the Gulf Stream and Labrador Current, join forces as the North Atlantic Current, which flows northeast almost 10° in latitude before turning east as the Subpolar Front, ultimately feeding the Labrador and Nordic Seas and the thermohaline overturning. After the Gulf Stream turns into the North Atlantic Current at the Grand Banks, its role shifts from a wind-driven current to a link in the large-scale thermohaline circulation. The processes governing this transition, in particular the continued transport north of mass and heat, are questions of considerable climatic importance. The North Atlantic Current is a very unusual western boundary current in that its mass transport decreases in the downstream direction.The mean path and annual shifting of the eastward flowing Gulf Stream is conjectured to result from a time-varying shelf-Slope Water overflow of waters from the Labrador shelf. As the volume transport increases in fall and deepens the Slope Water pycnocline, it forces the Gulf Stream south and deepens the Sargasso Sea thermocline as well. The timing of these steps governs the June maximum in baroclinic transport. There is some evidence that this ‘back-door’ gyre interaction may operate on interannual time scales as well. The question then arises whether the shelf-to-Slope Water Sea transport also plays a role in governing the separation of the Gulf Stream.The widely observed robustness of the width of the Gulf Stream appears to result from a tight balance between the release of available potential energy and the kinetic energy of the current. A broader current would release more energy than can be ‘disposed of’, while a narrower current requires more kinetic energy than is available to sustain it. It is shown that for plausible dissipation rates in the recirculation gyres, the amount of energy that needs to be expelled from the Gulf Stream is such a small fraction of that advected through as to be vitually undetectable, hence the stiffness of the current. 相似文献
12.
Using archived historical data on the temperature/salinity distribution, this paper describes the structure of the mean seasonal
and the actual field of the computed speed of sound in the Gulf Stream region. The formation of acoustic channels of large,
medium, and small size is considered, depending on the vertical thermohaline structure of waters. The paper provides statistical
characteristics of the sound speed field and acoustic channels of waters interacting in the Gulf Stream system.
Translated by Vladimir A. Puchkin. 相似文献
13.
Data on East Australian Current (EAC) warm-core eddies were obtained over the period 1976–1978 by the Department of Defence and the Commonwealth Scientific and Industrial Research Organization (CSIRO). In that time we have learned that warm eddies form by pinch-off of poleward EAC meanders, can coalesce with the EAC and appear generally similar to Gulf Stream, Kuroshio and other current system eddies. Two eddies were tracked over 1977–1978 with satellite buoys and one (eddy B) was repeatedly studied over eleven months. A deep winter core formed by winter convective cooling and the following summer a new surface mixed layer formed on top of the core. The seasonal changes have been analysed for heat content and changes in dynamic relief. The eddy decayed with a time constant of 650 ± 150 days, due to upwelling below the seasonal thermocline. Surface cooling had little effect on eddy lifetime. The eddy contracted horizontally, possibly after some interaction with the EAC, giving rise to eddy spin-up with increasing age. Surface currents increased after eleven months to 2.0 m s?1. The dynamic relief during summer was also apparently boosted by contact with the EAC. Eddy B was observed to coalesce with a new meander of the EAC rather than drift away to the south. It is proposed that the formation of these eddies is governed by the westward propagation of the baroclinic Rossby wave known as the Tasman Front. Pinch-off of eddies adjacent to the coast and the variable flow of the EAC may be caused by the baroclinic wave ‘breaking’ on the coast. The eddy formation rate is about two per year and most eddies coalesce with the EAC and do not escape to the south. Eddies coalesce and re-separate, creating many subsurface isothermal layers from old cores south of 34°S. 相似文献
14.
《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(24):2460-2473
Eddies in the Gulf of Alaska are important sources of coastal water and associated nutrients, iron, and biota to the high-nutrient, low-chlorophyll central Gulf of Alaska. Three primary eddy formation regions along the eastern boundary of the gulf have been identified, (from south to north, Haida, Sitka, and Yakutat). In the spring of 2005, three eddies (one of each type) were sampled soon after their formation. The subsurface eddy core water in all three eddies was defined by high iron concentrations and low dissolved oxygen compared with surrounding basin water. The Sitka and Yakutat core waters also exhibited a subsurface temperature maximum (mesothermal water) coincident in depth with the iron maximum, suggesting that eddies may play a role in the formation of temperature inversions observed throughout the Gulf of Alaska. The data suggest different formation regions, with the Yakutat eddy forming in shallow shelf water with riverine input, while the Sitka and Haida eddies appear to form in deeper water. 相似文献
15.
We consider the interannual variability of the intensity of the Gulf Stream and interannual fluctuations of seawater parameters in the Gulf Stream and in the Labrador Current during intense climate warming. We show that this intensity has increased during this period. The scales of fluctuations and their contribution to variance in the initial time series was determined from wavelet analysis of the Gulf Stream north wall. We noted a considerable decrease in water density of the main branch of the Gulf Stream, caused by the increase in temperature due to global climate warming, and an absence of trends in water density of the main branch of the Labrador Current. 相似文献
16.
Christopher S. Meinen Douglas S. Luther Molly O. Baringer 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(1):41-60
The stream-coordinates mean structure of the Gulf Stream at 68°W is derived using new methods for both defining stream coordinates and interpreting bottom pressure and inverted echo sounder travel times collected during the extensive Synoptic Ocean Prediction experiment. These new analyses provide pictures of the vertical structure of Gulf Stream flows that are demonstrably dynamically consistent with the density field at all depths, in contrast to previous work that relies on simple vertical interpolations to fill gaps between sparse current meter measurements. This new view of the Gulf Stream suggests a slightly higher total mean transport, with the increases coming from both baroclinic and barotropic components, and slightly stronger recirculation cells, particularly on the southern side. The recirculation of the Gulf Stream appears to have a weak baroclinic component, perhaps 10% of the total. A significant advantage of the methodology is the ability to obtain sensible vertical and horizontal gradients of currents and density so that the vertical and cross-stream structures of the components of the mean potential vorticity can be clearly imaged. One new feature from this calculation is that the along-stream gradient of the cross-stream velocity, a term that is often ignored in potential vorticity analyses, is non-negligible (though small) and is asymmetric about the current axis. Both the derived structure and implied dynamics of the circulation can be significantly altered by small changes to the method of calculating daily stream coordinates, e.g., by carefully filtering out observations in rings or not. Arrays of pressure-equipped inverted echo sounders provide the opportunity (at reasonable cost) for properly defining the stream coordinates of energetic jets such as the Gulf Stream. 相似文献
17.
Coupled patterns between fields of dynamic height and bottom pressure in the Japan/East Sea 总被引：1，自引：0，他引：1
Vertical coupling between shallow and deep mesoscale eddy processes in the southwestern Japan/East Sea is investigated using acoustic travel-time and bottom pressure measurements from a two-year deployment of an array of pressure-gauge-equipped inverted echo sounders. Canonical correlation analysis is applied to the simultaneously measured data to extract the coupled modes. The upper layer exhibits a migration of the Ulleung Warm Eddy, and correspondingly the deep potential vorticity in the Ulleung Basin adjusts in magnitude and sense to conserve potential vorticity. Coupling between meanders of strong upper currents and abyssal flows has been observed previously in the Gulf Stream during the Synoptic Ocean Prediction experiment. The evidence from our study strongly suggests that such coupling occurs also under much weaker flows. 相似文献
18.
Sperm whales (Physeter macrocephalus) are widely distributed in all oceans, but they are clumped geographically, generally in areas associated with high primary and secondary productivity. The warm, clear waters of the Sargasso Sea are traditionally thought to be low in productivity, however recent surveys have found large numbers of sperm whales there. The New England Seamount Chain bisects the north-western portion of the Sargasso Sea, and might influence the mesoscale eddies associated with the Gulf Stream; creating areas of higher productivity within the Sargasso Sea. We investigated the seasonal occurrence of sperm whales over Kelvin Seamount (part of the New England Seamount Chain) and how it is influenced by oceanographic variables. An autonomous recording device was deployed over Kelvin Seamount from May to June 2006 and November 2006 to June 2007. A total of 6505 hourly two-minute recordings were examined for the presence of sperm whale echolocation clicks. Sperm whales were more prevalent around Kelvin in the spring (April to June: mean=51% of recordings contained clicks) compared to the winter (November to March: mean=16% of recordings contained clicks). Sperm whale prevalence at Kelvin was related to chlorophyll-a concentration four weeks previous, eddy kinetic energy and month. The mesoscale activity associated with the Gulf Stream and the Gulf Stream׳s interaction with the New England Seamount Chain likely play an important role in sperm whale occurrence in this area, by increasing productivity and perhaps concentration of cephalopod species. 相似文献
19.
The results of the numerical modeling of the Gulf Stream region based upon the σ-model of the Institute of Computational Mathematics of the Russian Academy of Sciences are presented. The model reproduces the dynamics of the Gulf Stream meanders, the formation of warm and cold rings, and their further evolution. A simple physical mechanism leading to the westward drift of the rings of the main ocean mid-latitude frontal currents is considered. A simple theoretical model that makes it possible to estimate the westward ring drift is proposed. A comparison of the theory with the numerical results confirms the validity of the theoretical estimates and the physical adequacy of the model. 相似文献
20.
Lagrangian flow patterns in the vicinity of Cape Hatteras are examined using the tracks of 42 drifters drogued at 10 m depth and initially deployed over Georges Bank. The drifters predominantly move southwestward over the continental shelf and slope. North of Cape Hatteras, the drifters become entrained in the Gulf Stream and are carried eastward into the central Atlantic Ocean. There are two types of entrainment, abrupt and gradual. The first is characterized by a rapid change in drifter speed and an abrupt shift in drifter direction to the east. During such entrainment events, the radius of curvature of the drifter track is less than 30 km. The second type of entrainment is characterized by a gradual change in drifter direction with little change in speed. The radius of curvature of drifter tracks during such entrainment events is large (typically 50 km). The latter type occurs more frequently in summer and fall, when stratification is stronger. The drifter tracks further reveal that entrainment from the shelfbreak front/slope water system into the Gulf Stream may occur a significant distance north of Cape Hatteras, occasionally as far north as 38 °N, 200 km north of Cape Hatteras. Only two drifter tracks extend along the shelf past Diamond Shoals into the South Atlantic Bight. Four drifters are ejected from the Gulf Stream and recirculate over the slope. The observed time scale of recirculation ranges over 1–3 months. These results suggest that there are a variety of processes that determine the maximum southward penetration of Mid-Atlantic Bight shelf water before entrainment into the Gulf Stream as well as the cross-slope speed of entrainment. 相似文献