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1.
Ocean Dynamics - The circulation in the northern South China Sea (SCS) strongly responds to anticyclonic eddies that shed from the Kuroshio intruding across Luzon Strait. An eddy tracking algorithm... 相似文献
2.
Evolution of an anticyclonic eddy southwest of Taiwan 总被引：8，自引：1，他引：7
Tingting Zu Dongxiao Wang Changxiang Yan Igor Belkin Wei Zhuang Ju Chen 《Ocean Dynamics》2013,63(5):519-531
Satellite images of sea-surface temperature, surface chlorophyll a concentration, and sea-level anomaly, together with ocean reanalysis data of Asia and Indian–Pacific Ocean (AIPOcean1.0), are utilized to study the three-dimensional characteristics and evolution of an anticyclonic warm eddy adjacent to the southwest coast of Taiwan during October and November 2006. Originated from the Kuroshio intrusion in the Luzon Strait, but unlike previously found westward moving anticyclonic eddies (AE) in the northeastern South China Sea, this AE was so close to the Taiwan coast and stayed where it was formed for over 1 month until it dissipated. Energy analysis is utilized to study the evolution process of the AE, and it shows that the barotropic instability (BTI) and baroclinic instability introduced by the Kuroshio intrusion flow appear to be the main energy sources for the AE. Periodical enhancement/relaxation of local northeasterly monsoon and its associated negative wind stress curl modify the current patterns in this region, reinforce the intraseasonal variability of the Kuroshio intrusion flow, and act together with Kuroshio to form the AE. Eddies detected from AIPOcean1.0 data also show that AEs are most likely to be generated southwest of Taiwan during the transition period of summer monsoon to winter monsoon, and generally, the BTI of Kuroshio intrusion contributes more than the direct wind stress work to the increase of the eddy kinetic energy for the generation and growth of the AEs. 相似文献
3.
Combining Argo observations with satellite remote sensing data during the period of 2002–2014, the mean three-dimensional structures of mesoscale eddies on both sides of the Luzon Strait (LS) were obtained via a composite method and analyzed to statistically examine the influences of background marine environment and the Kuroshio current on the eddy structures. The significant signals of temperature and salinity anomalies within the composite eddies extend much deeper in the region east of the LS (zone E) than those in the region west of the strait (zone W) because of stronger eddy intensity and larger vertical gradients of background temperature and salinity in the deep layer in zone E. In the vertical structure of temperature anomaly within the eddies, two cores occur at around 200 and 400 dbar depths, respectively, in zone E and only one core is centered at about 100 dbar in zone W. There is a clear three-core sandwich pattern in the vertical structure of salinity anomaly within the eddies in zone E. The Kuroshio water trapped in the eddy is responsible for abnormally positive salinity anomaly in the surface layer of the anticyclonic eddy center in zone W. On both sides of the LS, an asymmetric dipole structure in the surface layer gradually turns into a monopole one at depths, which resulted from the competition between horizontal advection effect and eddy pumping effect. The Kuroshio current influences the distribution patterns of isotherms and isohalines and enhances background temperature and salinity horizontal gradients on both sides of the LS, determining the orientations of dipole temperature and salinity structures within eddies. 相似文献
4.
Numerical study of upper ocean response to a typhoon moving zonally across the Luzon Strait 总被引：1，自引：0，他引：1
The Luzon Strait (LS) is a wide channel between Taiwan and the Luzon islands. Eastward of the LS, the Kuroshio Current (KC)
flows northward along the eastern coasts of Luzon and Taiwan. A typhoon is a strong and localized low-pressure weather system
that occurs frequently in the vicinity of the Taiwan area. One typical typhoon track, passing through the seas surrounding
Taiwan, is a zonal path across the LS. The satellite measured SST, corresponding to typhoons Pabuk (5 Aug. 2007–12 Aug. 2007)
and Dujuan (29 Aug. 2003–5 Sep. 2003), which both moved along this path, demonstrated that a classic right bias cooling occurs
to the north of the storm track, during the typhoon forced period. However, some cold anomaly water also present toward left
(south) of the storm track east of the LS in the relaxation period. This paper adopted a three-dimensional hydrostatic primitive
equation model to study the possible causes of this southward transport of cold waters. Both model results and the observed
SST anomaly revealed that the strength of the upper ocean cooling depends on whether a resonant regime between the typhoon
winds and the near-inertial currents can be excited. To the east of the LS, the convergence between the warm Kuroshio water
and the cold wakes in the poststorm period will enhance the southward spreading of cold anomaly water. The enhanced vertical
mixing, induced by the southward propagation of nearly inertial waves associated with the cold wakes, can also produce some
cold anomaly to the south of a storm track in the poststorm period. Both mechanisms can contribute to the occurrence of some
cold anomaly water to the south of the storm track east of the KC. To the west of the LS, the convergence between the warm
Kuroshio water and the cold upwelling water from the northern South China Sea can further strengthen the Kuroshio front in
the LS. 相似文献
5.
Previous investigations have suggested that wind stress curl, the balance of influx- and outflux-induced upwelling, as well
as a positive vorticity source fed from the left flank of the Kuroshio are all possible mechanisms that contribute to a persistent
cyclonic gyre in the South China Sea (SCS). Studies have also suggested that the loop current that forms from the Kuroshio
intrusion in the Luzon Strait, similar to the Loop Current in the Gulf of Mexico (GOM), has rarely been observed in the northern
SCS. In this research, an idealized numerical model driven by annual mean wind stress was adopted to investigate the relative
importance of dynamic processes that control the mean flow pattern of Kuroshio in the Luzon Strait and regulate circulation
in the SCS. An analysis of results drawn from numerical experiments suggests that the three mechanisms are of approximately
equal importance in the formation of the persistent cyclonic gyre in the northern SCS. Unlike the Gulf Stream which enters
the Gulf of Mexico through the Yucatan Channel, the two topographic ridges that align nearly meridionally in the Luzon Strait
keep the Kuroshio flowing roughly northward without distinct intrusion into the SCS. Unsurprisingly, an anticyclonic loop
current similar to the Gulf Stream pathway in the GOM was barely observed in the northern SCS. 相似文献
6.
Kuroshio intrusion into the South China Sea (SCS) has different forms. In this study, a Kuroshio SCS Index (KSI) is defined
using the integral of geostrophic vorticity from 118° to 121° E and from 19° to 23° N. Three typical paths (the looping path,
the leaking path, and the leaping path) were identified based on the KSI derived from the weekly satellite Absolute Dynamic
Topography from 1993 to 2008. The KSI has a near normal distribution. Using ±1 standard deviation (σ) as the thresholds, the leaking path is the most frequent form with the probability of occurrence at 68.2%, while the probabilities
of occurrence for the looping path and the leaping path are 16.4% and 15.4%, respectively. Similar analysis is also conducted
on the daily Hybrid Coordinate Ocean Model (HYCOM) Global Analysis from 2004 to 2008. The results are generally consistent
with the KSI analysis of the satellite data. The HYCOM data are further analyzed to illustrate patterns of inflows/outflows
and the maximum/minimum salinity as representatives of the subsurface/intermediate waters. The Kuroshio bending and the net
inflow through the Luzon Strait reduce from the looping path to the leaking path to the leaping path. However, the Kuroshio
subsurface water intrudes farthest into the SCS for the leaking path. Vorticity budget associated with the different intrusion
types is then analyzed. The tilting of the relative vorticity, the stretching of the absolute vorticity, and the advection
of planetary vorticity are important for the change of vorticity, whereas the baroclinic and frictional contributions are
three orders smaller. 相似文献
7.
Using a new functional analysis tool, multiscale window transform(MWT), and the MWT-based localized multiscale energetics analysis and canonical transfer theory, this study reconstructs the Kuroshio system on three scale windows, namely,the mean flow window, the interannual-scale(low-frequency) window, and the transient eddy window, and investigates the climatological characteristics of the intricate nonlinear interactions among these windows. Significant upscale energy transfer is observed east of Taiwan, where the mean Kuroshio current extracts kinetic energy from both the interannual and eddy windows.It is found that the canonical transfer from the interannual variability is an intrinsic source that drives the eddy activities in this region. The multiscale variabilities of the Kuroshio in the East China Sea(ECS) are mainly controlled by the interaction between the mean flow and the eddies.The mean flow undergoes mixed instabilities(i.e., both barotropic and baroclinic instabilities) in the southern ECS, while it is barotropically stable but baroclinically unstable to the north. The multiscale interactions are found to be most intense south of Japan, where strong mixed instabilities occur; both the canonical transfers from the mean flow and the interannual scale are important mechanisms to fuel the eddies. It is also found that the interannual-scale energy mainly comes from the barotropically unstable jet, rather than the upscale energy transfer from the high frequency eddies. 相似文献
8.
AVHRR satellite imagery of the southern Mid-Atlantic Bight during May 1993 revealed a large area of cold water over the shelf break and slope that appeared to spin up into a series of southward propagating anticyclonic eddies. The eddies had diameters of 35–45 km at the surface and moved southward at about 20 cm/sec. A radial TOYO CTD (to 50m) and ADCP velocity (to 400m) transect was conducted across the southern-most of these eddies. The upper 50 meters had minimum temperatures of less than 7°C and salinities of about 33 pss, characteristics similar to cold pool waters usually found over the continental shelf. ADCP velocity data from one of the eddies revealed anticyclonic flow extending to a depth of about 250m. The transport of cold pool water by the eddies was estimated to be 0.1 to 0.2 Sv which is of the same order as the annual mean alongshore transport of shelf water in this region. The origin of the deeper water within the eddy is unlikely to be the continental shelf because the shelf break is less than 100 m. The depth and velocity profiles along the TOYO transect were consistent with the constant potential vorticity eddy model of Flierl (1979) although the source of the eddy kinetic energy is uncertain. The cause for the exodus of cold pool water from the shelf, which extended northward to at least 38°N, is unclear but must involve the establishment of an alongshore baroclinic pressure gradient against the usual southwestward shelf flow. It is possible that the intrusion of Gulf Stream waters onto the shelf near Cape Hatteras was a precursor of this off shelf transport. The southern-most eddy was marked by high biological productivity and very high oxygen supersaturation. The phytoplankton bloom detected within the exported cold pool water, located over the continental slope, suggests a mechanism whereby production fueled by nutrients derived from the shelf can be locally exported into deep water. 相似文献
9.
The Kuroshio current is well known for generating cold wakes behind islands over Izu Ridge in Northwestern Pacific. Observational data from the geostationary Himawari-8 satellite for 2015–2017 revealed the occurrence of cold waters during the period when the Kuroshio current flows away from the islands. With a focus on tidal currents, this study presents an investigation of dynamical processes responsible for the formation of areas with low sea surface temperature (SST) through the adoption of a high-resolution numerical ocean model for an event that happened in July 2017. Areas with cold water emerged only when tidal currents are included in the numerical model. The model results indicate the cold surface waters are formed in the vicinity of the islands because of upwelling and vertical mixing. Qualitative features of the cold water formation for each island are found to depend on its size, topography, and ambient currents. Near Kozu Island, the tidal excursion is large enough to cause eddy shedding. These shed eddies are stirred by tidal currents to extend the surface cooling effect to wider areas. Near Hachijo Island, a persistent wake is formed by the ambient northward current. Inclusion of tidal currents destabilizes the wake, and consequently leads to the formation of a low SST area, although no clear eddy shedding is detected. The flow patterns around the islands are classified using an additional non-dimensional parameter, defined as the ratio between tidal excursion and island diameter.
相似文献10.
This study used a 1.5-layer reduced-gravity numerical model to investigate the nonlinear dynamics of Kuroshio intrusion into the Luzon Strait. The model results suggested that both basin-scale wind curl and lateral friction are the primary factors that control the transformation of the flow, although inertia also plays an important role. Using an idealized model, both the mechanism via which the flow pattern changes depending on the two primary factors and the occurrence of hysteresis were investigated. It was established that the transformation of the Kuroshio flow field between the four previously reported flow patterns (i.e., leaping across, current looping, eddy shedding, and branch intruding) can be explained under a unified theoretical framework. A diagram is proposed to explain how the flow field transforms between the four patterns from a certain prior state when varying the values of the controlling factors. 相似文献
11.
Dmitry V. Stepanov 《Ocean Dynamics》2018,68(10):1353-1370
Based on an eddy-permitting numerical model, the mesoscale variability in the East-Sakhalin Current is investigated during the winter-spring period. Analysis of necessary conditions for the development of baroclinic instability showed that the nearshore component of the East-Sakhalin Current is potentially baroclinic unstable in the first half-year. The simulated circulation uncovered a generation of anticyclonic eddies on the eastern Sakhalin shelf. It was established that a spatial scale of these eddies and the first baroclinic Rossby radius of deformation are values of the same order; a lifetime of these eddies varies from 4 to 6 weeks, given the Rossby number varies from 0.05 to 0.2. Analysis of the rate of eddy energy conversion on the eastern Sakhalin shelf showed that the generation of the revealed mesoscale eddies results from, mainly, baroclinic instability, whereas barotropic instability can be both favoring and preventing to the generation of these eddies. 相似文献
12.
Variability analysis of Kuroshio intrusion through Luzon Strait using growing hierarchical self-organizing map 总被引：3，自引：0，他引：3
An advanced artificial neural network classification algorithm is applied to 18?years of gridded mean geostrophic velocity multi-satellite data to study the Kuroshio intrusion into the South China Sea through the Luzon Strait. The results suggest that the Kuroshio intrusion may occur year round. However, intrusion is not the major characteristic of the region. The intrusion mode occurs only 25.8?% of the time. Winter intrusion events are more frequent than summer events. Both stronger intrusion (which is related to wind speed) and weaker intrusion (which may be related to the upstream Kuroshio transport) may occur during winter, but stronger intrusion is dominant. In summer, the Kuroshio intrusion is almost the weaker type. The Kuroshio intrusion through the Luzon Strait usually occurs when the Pacific decadal oscillation index is positive (72.1?% of the time). This study shows that growing hierarchical self-organizing map is a useful tool for analyzing Kuroshio intrusion through the Luzon Strait. 相似文献
13.
The structure and variability of the currents in the Luzon Strait during spring of 2002 are studied, based on the current measurements at the average position of the mooring station (20°49′57"N, 120°48′12"E) from March 17 to April 15, 2002, satellite geostrophic currents in the Luzon Strait, and the spectral analyses, using the maximum entropy method. The subtidal currents at the mooring station show de-creased amplitudes downward with an anti-cyclonic rotation, suggesting that the currents enter and exit t... 相似文献
14.
Benchmarking the mesoscale variability in global ocean eddy-permitting numerical systems 总被引：1，自引：1，他引：0
Andrea Cipollone Simona Masina Andrea Storto Doroteaciro Iovino 《Ocean Dynamics》2017,67(10):1313-1333
The role of data assimilation procedures on representing ocean mesoscale variability is assessed by applying eddy statistics to a state-of-the-art global ocean reanalysis (C-GLORS), a free global ocean simulation (performed with the NEMO system) and an observation-based dataset (ARMOR3D) used as an independent benchmark. Numerical results are computed on a 1/4 ° horizontal grid (ORCA025) and share the same resolution with ARMOR3D dataset. This “eddy-permitting” resolution is sufficient to allow ocean eddies to form. Further to assessing the eddy statistics from three different datasets, a global three-dimensional eddy detection system is implemented in order to bypass the need of regional-dependent definition of thresholds, typical of commonly adopted eddy detection algorithms. It thus provides full three-dimensional eddy statistics segmenting vertical profiles from local rotational velocities. This criterion is crucial for discerning real eddies from transient surface noise that inevitably affects any two-dimensional algorithm. Data assimilation enhances and corrects mesoscale variability on a wide range of features that cannot be well reproduced otherwise. The free simulation fairly reproduces eddies emerging from western boundary currents and deep baroclinic instabilities, while underestimates shallower vortexes that populate the full basin. The ocean reanalysis recovers most of the missing turbulence, shown by satellite products , that is not generated by the model itself and consistently projects surface variability deep into the water column. The comparison with the statistically reconstructed vertical profiles from ARMOR3D show that ocean data assimilation is able to embed variability into the model dynamics, constraining eddies with in situ and altimetry observation and generating them consistently with local environment. 相似文献
15.
LI TieGang SUN RongTao ZHANG DeYu LIU ZhenXia LI Qing & JIANG Bo Key Laboratory of Marine Geology Environment Institute of Oceanology Chinese Academy of Sciences Qingdao China Graduate School of Chinese Academy of Sciences Beijing China School of Resources & Environment Engineering Shandong University of Technology Zibo China The First Institute of Oceanography State Oceanic Administration Qingdao China 《中国科学D辑(英文版)》2007,50(5):725-735
The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon isotope records of mixed layer dweller G. ruber and thermocline dweller N. dutertrei in piston core CSH1 and core DGKS9603 collected separately from the Tsushima warm current and the Kuroshio dominated area. The result showed that the Tsushima warm current vanished in the lowstand period during 40―24 cal ka BP, while the Kuroshio still flowed across the Okinawa Trough, arousing strong upwelling in the northern Trough. Meanwhile, the influence of freshwater greatly increased in the northern Okinawa Trough, as the broad East China Sea continental shelf emerged. The freshwater reached its maximum during the last glacial maximum (LGM), when the upwelling obviously weakened for the lowest sea-level and the depression of the Kuroshio. The modern Tsushima warm current began its development since 16 cal ka BP, and the impact of the Kuroshio increased in the middle and north- ern Okinawa Trough synchronously during the deglaciation and gradually evolved as the main water source of the Tsushima current. The modern Tsushima current finally formed at about 8.5 cal ka BP, since then the circulation structure has been relatively stable. The water of the modern Tsushima cur- rent primarily came from the Kuroshio axis. A short-term wiggle of the current occurred at about 3 cal ka BP, probably for the influences from the enhancement of the winter monsoon and the depression of the Kuroshio. The cold water masses greatly strengthened during the wiggle. 相似文献
16.
Sea surface height and transport stream function of the South China Sea from a variable-grid global ocean circulation model 总被引：8，自引：0，他引：8
The study on the South China Sea (SCS) circulation has a history of more than 40 years. Nevertheless, the SCS circulation is not fully understood compared with the Bohai Sea, Yellow Sea and East China Sea (ECS). Many numerical studies on the SCS circulati… 相似文献
17.
The circulation in the Straits of Florida is dominated by the throughflow of the Florida Current, as modified by tidal flows,
responses to atmospheric cold front and extratropical cyclone (easterly wave and tropical cyclone) passages in winter (summer),
and intrinsic mesoscale variability due to instabilities of the Florida Current front and jet system. Monthly meanders of
the Florida Current, persistent oceanic fronts associated with the Florida Current’s baroclinic jet, and frontal eddies shed
weekly by the Florida Current are the primary mesoscale features. A limited area model (Princeton Ocean Model: POM) is implemented
to cover the Straits of Florida with a curvilinear grid that resolves the mesoscale structure, especially where the baroclinic
flow is locked to steep topography in a 90 degree bend of the Straits. Florida Current cyclonic frontal eddies are spawned
spontaneously, grow as they translate downstream, interact with shelf waters, and exhibit the same space-time attributes that
characterize their observed counterparts, as evidenced by satellite imagery, shipboard synoptic mapping, coastal HF radar,
and moored time series. Here, a deeper understanding is attempted for the frontal eddy kinematics and dynamics by examining,
for example, their sensitivity to model parameter values, synoptic versus monthly atmospheric forcing, and other determinants
of the flow. The mean flow shears are concentrated along the shelfbreak, where these frontal eddies are trapped, favoring
the formation of the eddies by mean flow instabilities. In particular, it is found that the Florida Current frontal eddies
exist independent of the wind-forcing considered (i.e., no winds, monthly winds, and synoptic (but not mesoscale) winds);
however, they are modulated by the synoptic wind-forcing. Nevertheless, intriguingly, the frontal eddies have the same weekly
time scale as the weather cycle. 相似文献
18.
I-Huan Lee Dong Shan Ko Yu-Huai Wang Luca Centurioni Dong-Ping Wang 《Ocean Dynamics》2013,63(9-10):1027-1040
The relationship between the Kuroshio volume transport east of Taiwan (~24°N) and the impinging mesoscale eddies is investigated using 8-year reanalysis of a primitive equation ocean model that assimilates satellite altimetry and SST data. The mean and fluctuations of the model Kuroshio transport agree well with the available observations. Analysis of model dynamic heights and velocity fields reveals three dominant eddy modes. The first mode describes a large eddy of ~500 km in diameter, centered at ~22° N. The second mode describes a pair of the north–south counter-rotating eddies of?~?400 km in diameter each, centered at 23° and 20° N, respectively. The third mode describes a pair of the east–west counter-rotating eddies of?~?300 km in diameter each, centered at 21° N. The associated velocity fields indicate eddies extending to 600–700 m in depth with vertical shears concentrated in the upper 400 m. All three modes and the model Kuroshio transport have similar dominant timescales of 70–150 days and generally are coherent. The decreased Kuroshio volume transports typically are associated with the impinging cyclonic eddies and the increased transports with the anticyclonic eddies. Selected drifter trajectories are presented to illustrate the three eddy modes and their correspondence with the varying Kuroshio transports. 相似文献
19.
Eddy resolving modelling of the Gulf of Lions and Catalan Sea 总被引：1，自引：1，他引：0
The generation process of strong long-lived eddies flowing southwestwards along the Catalan slope was revealed through numerical
modelling and in situ observations. Careful analyses of a particular event in autumn 2007 demonstrated a link between a “LATEX”
eddy, which remained in the southwestern corner of the Gulf of Lions and a “CATALAN” eddy, which moved along the Catalan Shelf,
since the death of the former gave birth to the latter. The origin of such eddies was found to be an accumulation of potential
energy in the southwestern corner of the Gulf of Lions: under the influence of the negative wind stress curl associated with
the Tramontane, a warm and less dense water body can be isolated and fed by a coastal current carrying warm water from the
Catalan Sea. In summer, this structure can grow and intensify to generate a strong anticyclonic eddy. After a long period
of Tramontane, a burst of southeasterlies and northerlies appeared to detach the “LATEX” eddy, which flowed out of the Gulf
of Lions, migrating along the Catalan continental slope and continued into the Balearic Sea as the “CATALAN” eddy. 相似文献
20.
Effects of mesoscale eddies on the marine ecosystem in the Kuroshio Extension (KE) region are investigated using an eddy-resolving
coupled physical-biological model. The model captures the seasonal and intra-seasonal variability of chlorophyll distribution
associated with the mesoscale eddies, front variability, Kuroshio meanders, and upwelling. The model also reproduces the observed
interannual variability of sea surface height anomaly (SSHA) in the KE region along a zonal band of 32–34°N from 2002 to 2006.
The distribution of high surface chlorophyll corresponds to low SSHA. Cyclonic eddies are found to detach from the KE jet
near 150°E and 158°E and propagate westward. The westward propagating cyclonic eddies lift the nutrient-rich thermocline into
the euphotic zone and maintain high levels of chlorophyll in summer. In the subsurface layer, the pattern in chlorophyll is
influenced by both lateral and vertical advection. In winter, convection inside the eddy entrains high levels of nutrients
into the mixed layer, increasing production, and resulting in high chlorophyll concentration throughout the surface mixed
layer. There is significant interannual variability in both the cyclonic eddy activity and the surface phytoplankton bloom
south of the KE jet, although whether or not there is a causal link is unclear. 相似文献