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1.
Newly formed North Pacific Tropical Water (NPTW) is carried to the Philippine Sea (PS) by the North Equatorial Current (NEC) as a subsurface salinity maximum. In this study its spreading and salinity change processes are explored using existing hydrographic data of the World Ocean Database 2009 and Argo floats. Spreading of NPTW is closely associated with the transports of the NEC, Mindanao Current (MC), and Kuroshio. Estimated for subsurface water with salinity S greater than 34.8?psu, the southward (northward) geostrophic transport of NPTW by the MC (Kuroshio) at 8°N (18°N) is about 4.4 (5.7)?Sv (1?Sv?=?106?m3?s?1), which is not sensitive to reference level choice. Fields of salinity maximum, geostrophic current, sea level variation, and potential vorticity suggest that the equatorward spreading of NPTW to the tropics is primarily afforded by the MC, whereas its poleward spreading is achieved by both the Kuroshio transport along the coast and open-ocean mesoscale eddy fluxes in the northern PS. The NPTW also undergoes a prominent freshening in the PS. Lying beneath fresh surface water, salinity decreases quicker in the upper part of the NPTW, which gradually lowers the salinity maximum of NPTW to denser isopycnals. Salinity decrease is especially fast in the MC, with along-path decreasing rate reaching O (10?7?psu?s?1). Both diapycnal and isopycnal mixing effects are shown to be elevated in the MC owing to enhanced salinity gradient near the Mindanao Eddy. These results suggest intensive dispersion of thermal anomalies along the subtropical-to-tropical thermocline water pathway near the western boundary. 相似文献
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The interannual variability of the temperature structure of the Kuroshio Extension is studied by establishing time series for the period 1950 to 1970 and then comparing it with the time series of sea level differences across the North Equatorial Current obtained by Wyrtki (1975). First, the present analysis shows a significant correlation between the interannual fluctuation of the Kuroshio Extension and the eddy activity south of the Kuroshio axis, suggesting the importance of the eddy-driven mechanism. Secondly, spectral analysis shows close connections between the Kuroshio Extension and the North Equatorial Current with a reasonable time lag of about 1.5 years. This time lag of the mid-latitude variability is also supported by other independent data. In particular, the present preliminary study strongly suggests that the bimodal behavior of the Kuroshio path south of Japan and the intensity of the Kuroshio Countercurrent are closely connected with the Southern Oscillation/El Niño. 相似文献
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Oceanic variabilities off Mindanao Island, Philippines where the North Equatorial Current branches into the Kuroshio and the Mindanao Current were measurerd for a period from 14 Feb.–1 Jun. 1992 by the oceean acoustic tomography (OAT). From the beginning of April, the travel time of acoustic rays propagating over a horizontal distance of about 250km, through the depth range of 80–4700 m around the underwater sound channel began to decrease, implying a warming of water. This variability was also confirmed with the results of temperature measurement at the sites where a sound source and receiver were located. The TOGA/TAO array data show that the OAT experiment was done when the 1991–1992 El Nino was at a decaying stage and the resulting warming-up of water occurred at the western Pacific. This study provides us a first evidence of ENSO-related variabilities detected by the OAT. 相似文献
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Impact of the winter cooling on the variability of the thermohaline characteristics of the active layer in the Black Sea 总被引：1，自引：0，他引：1
The influence of the winter atmospheric forcing on the interannual variability of the Black Sea’s active layer’s thermohaline
structure during 1982–2008 is investigated. The results are based on the combined analysis of the hydrological measurements
from a ship, satellite measurements of the sea’s surface temperature (SST), and the NCEP/NCAR reanalysis data for the surface
air temperature (SAT). A high correlation between the variability of the winter mean SST/SAT and the thermohaline characteristics
of the active layer during the following warm season was found. It is shown that the winter atmospheric forcing significantly
affects the variability of the temperature, salinity, and density down to the 150–200 m depth, and this has to be considered
in the analysis of the interannual and long-term variability of the Black Sea’s active layer. 相似文献
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Low-frequency variability of the North Equatorial Current bifurcation in the past 40 years from SODA 总被引：1，自引：1，他引：0
The low-frequency variability of the North Equatorial Current (NEC) bifurcation during 1958 to 2001 was investigated with the Simple Ocean Data Assimilation (SODA) 2.0.2 dataset.In agreement with recent observations,the NEC bifurcation latitude (NBL) shifted northward as depth increases, from about 12.7°N near the surface to about 17.1°N at depths around 500 m for the annual average. This study reveals that the interannual variations of NBL,with five years period,mainly focused on the upper 500 m with amplitude increasing as depth increased.The NBL shifted southward in the past 40 years,which was more significant in the subsurface at more than -0.02°/a.The NBL manifests itself in the transports of NMK (NEC-Mindanao Current (MC)-Kuroshio) system in strong relationship with MC (0.7) and Kuroshio (-0.7).The EOF analysis of meridional velocity off the Philippine coast shows that the first mode,explaining 62% of variance and 5 years period,was highly correlated with the southward shift of NBL with coefficient at about 0.75.The southward shift of NBL consists with the weakening of MC and strengthening of Kuroshio,which exhibited linear trends at -0.24Sv/a and 0.11Sv/a.Both interannual variation and trend of NBL were closely related to the variation of NMK system. 相似文献
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Using the 28°C isotherm to define the Western Pacific Warm Pool(WPWP), this study analyzes the seasonal variability of the WPWP thermohaline structure on the basis of the monthly-averaged sea temperature and salinity data from 1950 to 2011, and the dynamic and thermodynamic mechanisms based on the monthly-averaged wind,precipitation, net heat fluxes and current velocity data. A DT=–0.4°C is more suitable than other temperature criterion for determining the mixed layer(ML) and barrier layer(BL) over the WPWP using monthly-averaged temperature and salinity data. The WPWP has a particular thermohaline structure and can be vertically divided into three layers, i.e., the ML, BL, and deep layer(DL). The BL thickness(BLT) is the thickest, while the ML thickness(MLT) is the thinnest. The MLT has a similar seasonal variation to the DL thickness(DLT) and BLT.They are all thicker in spring and fall but thinner in summer. The temperatures of the ML and BL are both higher in spring and autumn but lower in winter and summer with an annual amplitude of 0.15°C, while the temperature of the DL is higher in May and lower in August. The averaged salinities at these three layers are all higher in March but lower in September, with annual ranges of 0.41–0.45. Zonal currents, i.e., the South Equatorial Current(SEC)and North Equatorial Counter Current(NECC), and winds may be the main dynamic factors driving the seasonal variability in the WPWP thermohaline structure, while precipitation and net heat fluxes are both important thermodynamic factors. Higher(lower) winds cause both the MLT and BLT to thicken(thin), a stronger(weaker)NECC induces MLT, BLT, and DLT to thin(thicken), and a stronger(weaker) SEC causes both the MLT and BLT to thicken(thin) and the DLT to thin(thicken). An increase(decrease) in the net heat fluxes causes the MLT and BLT to thicken(thin) but the DLT to thin(thicken), while a stronger(weaker) precipitation favors thinner(thicker)MLT but thicker(thinner) BLT and DLT. In addition, a stronger(weaker) NECC and SEC cause the temperature of the three layers to decrease(increase), while the seasonal variability in salinity at the ML, BL, and DL might be controlled by the subtropical cell(STC). 相似文献
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南海中尺度涡温盐结构的季节特征及形成机制 总被引：2，自引：0，他引：2
本文利用最新的涡旋数据集和ARMOR3D数据，研究了南海中尺度涡温盐结构的季节特征及形成机制。合成分析的结果表明，在冬季，涡旋引起温度异常的水平分布在50米以浅表现为类似偶极型分布，而在50m以深则趋向于中心对称分布；在夏季，温度异常的水平分布均表现为中心对称的特征。涡旋引起盐度异常的水平分布也具有类似的季节特征，但是偶极型中的不对称性相对较弱。在垂向上，涡旋所致的温度异常表现为单层结构，而盐度异常则为三层结构。进一步的分析表明，涡旋所致温盐异常的垂向分布特征与背景温盐的垂向分层有关；而在50m以浅，温盐异常的水平分布的不对称特征主要由背景温盐场的水平平流所致。 相似文献
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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
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Seasonal variability of the Mindanao Current determined using mooring observations from 2010 to 2014
Fujun Wang Qingye Wang Dunxin Hu Fangguo Zhai Shijian Hu 《Journal of Oceanography》2016,72(5):787-799
A mooring was deployed east of Mindanao Island at 8°N, 127°3′E from December 2010 to August 2014 to collect direct measurements of the Mindanao Current (MC). The Acoustic Doppler Current Profiler (ADCP) fixed on the main float shows that the MC is a strong and stable southward flow with a standard deviation less than 21 cm/s in the upper 500 m. The core flows between depths of 50 and 100 m with a maximum mean speed of 78 cm/s at 100 m. The seasonal variability of MC varies interannually and is depth-dependent. Although it takes a double-peak structure in the upper 200 m with two maxima in April and June and one minimum in October, the MC velocity has its maximum during boreal summer (June) and a minimum in autumn (September) when a 100-day low-pass filter is applied to remove intraseasonal signals. The semiannual signals are mainly limited between 200 and 350 m. The Asian monsoon intensifies the wind-driven sea-surface height anomaly (SSHA) east of Mindanao Island, and the resulting sharp slope induces meridional flow with large variability. Rossby waves and the boundary effect weaken the contribution of wind, stabilizing the flow of MC. The MC is determined by the zonal gradient of the SSHA rather than the SSHA itself, suggesting a possible inconsistency in seasonality between the Mindanao Eddy (ME) and MC. The semiannual ME signal plays an important role in the seasonal variability of MC. 相似文献
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利用SODA(Simple Ocean Data Assimilation)数据、XBT(Expendable Bathythermograph)观测数据和绕岛环流理论(island rule)诊断计算结果评估了一个涡相容(eddy-permitting)全球海洋环流模式——LICOM对南海贯穿流及南海上层热含量的模拟能力,同时利用模式输出探讨了南海贯穿流对南海上层热含量的影响。NEC(North Equatorial Current)分叉的垂向结构、南海内区环流的季节和吕宋海峡体积输送的年际变化等分析结果都表明,LICOM能获取西北太平洋-印尼海域环流和南海贯穿流的合理模拟结果。模式模拟的南海上层热含量季节变化与观测及同化数据都表现出良好的一致性,尤其在南海内区。相关分析表明,吕宋海峡热输送主要控制着南海内区上层的热含量变化,两者呈显著负相关,这进一步证实了南海贯穿流作为一支冷平流调制着南海上层热含量变化的重要事实。 相似文献
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Konstantin A. Rogachev 《Progress in Oceanography》2000,47(2-4)
The objective of this research is to describe physical processes which are the cause of the recent variability of the Pacific western subarctic waters. Rapid thermohaline changes have occurred within the Oyashio and Kamchatka Current during the last decade. This variability has included a warming of the Kamchatka Current warm intermediate layer, but a cooling and freshening of the upper layer in the Oyashio and Sea of Okhotsk. The example presented here uses data obtained during the Canada/Russia INPOC and WOCE projects, as well as the new Russian studies with high resolution station grid.The possible physical mechanism that generated the upper layer freshening during the thermohaline transition is examined. Major components of the fresh water budget of the Okhotsk Sea are considered in order to describe the dramatic changes in salinity which have recently occurred in the Pacific subarctic. Significant changes in precipitation and other fresh water inputs are demonstrated. It is suggested that upper layer of the Oyashio and Kamchatka Current became cooler and fresher because of the export of cold, fresher waters from the Bering and Okhotsk seas. These waters from the marginal seas have cooled the bottom of the halocline, reducing evaporation and acting as a feedback that has kept the upper layer of the western subarctic boundary currents fresh. It is also shown that the outflow of the cold Sea of Okhotsk water has changed its path during this recent thermohaline transition. 相似文献
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2009-2010年冬季南海东北部中尺度过程观测 总被引：2，自引：1，他引：1
根据南海北部陆架陆坡海域2009-2010年冬季航次的CTD调查资料,发现西北太平洋水在上层通过吕宋海峡入侵南海,其对南海东北部上层水体温盐性质的影响自东向西呈减弱趋势,影响范围可达114°E附近。入侵过程中受东北部海域反 气旋式涡旋(观测期间,其中心位于20.75°N,118°E附近) 的影响,海水的垂向和水平结构发生了很大变化,特别是涡旋中心区域,上层暖水深厚,混合层和盐度极大值层显著深于周边海域。该暖涡在地转流场、航载ADCP观测海流及卫星高度计资料中均得到了证实。暖涡的存在还显著影响了海水化学要素的空间分布,暖涡引起的海水辐聚将上层溶解氧含量较高的水体向下输运,使次表层的暖涡中心呈现高溶解氧的分布特征。 相似文献
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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
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《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(7):1303-1332
A time series of a standard hydrographic section in the northern Rockall Trough spanning 23 yr is examined for changes in water mass properties and transport levels. The Rockall Trough is situated west of the British Isles and separated from the Iceland Basin by the Hatton and Rockall Banks and from the Nordic Seas by the shallow (500 m) Wyville–Thompson ridge. It is one pathway by which warm North Atlantic upper water reaches the Norwegian Sea and is converted into cold dense overflow water as part of the thermohaline overturning in the northern North Atlantic and Nordic Seas. The upper water column is characterised by poleward moving Eastern North Atlantic Water (ENAW), which is warmer and saltier than the subpolar mode waters of the Iceland Basin, which also contribute to the Nordic Sea inflow. Below 1200 m the deep Labrador Sea Water (LSW) is trapped by the shallowing topography to the north, which prevents through flow but allows recirculation within the basin. The Rockall Trough experiences a strong seasonal signal in temperature and salinity with deep convective winter mixing to typically 600 m or more and the formation of a warm fresh summer surface layer. The time series reveals interannual changes in salinity of ±0.05 in the ENAW and ±0.04 in the LSW. The deep water freshening events are of a magnitude greater than that expected from changes in source characteristics of the LSW, and are shown to represent periodic pulses of newer LSW into a recirculating reservior. The mean poleward transport of ENAW is 3.7 Sv above 1200 dbar (of which 3.0 Sv is carried by the shelf edge current) but shows a high-level interannual variability, ranging from 0 to 8 Sv over the 23 yr period. The shelf edge current is shown to have a changing thermohaline structure and a baroclinic transport that varies from 0 to 8 Sv. The interannual signal in the total transport dominates the observations, and no evidence is found of a seasonal signal. 相似文献
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The statistical characteristics and vertical thermohaline properties of mesoscale eddies in the Bay of Bengal are studied from the view of satellite altimetry data and Argo profiles. Eddy propagation preferences in different lifetimes, eddy evolution process, and geographical distribution of eddy kinetic properties are analyzed in this area. Eddies exist principally in the western Bay of Bengal, and most of them propagate westward. There is a clear southward(equatorward) preference for eddies with long lifetimes, especially for cyclones. Moreover, the eddies in different areas of the bay show different north-southward preferences. Evolution of eddy kinetic properties with lifetime shows that eddies have the significant three-stage feature: the growth period in the former one-fifth lifetime, the stable period in the middle two-fifth to four-fifth lifetime, and the dying period in the last one-fifth lifetime. Large-amplitude and high-intensity eddies occur only in the relatively confined regions of highly unstable currents, such as the East Indian Coastal Current and eastern Sri Lanka. Based on Argo profile data and climatology data, the eddy synthesis method was used to construct three-dimensional temperature and salt structures of eddies in this area. The mean temperature anomaly is negative/positive to the cyclonic/anticyclonic eddies in the upper 300×10~4 Pa, and below this depth, the anomaly becomes weak. The salinity structures of positive anomalies inside cyclonic eddies and negative anomalies inside anticyclonic eddies in the Bay of Bengal are not consistent with other regions. Due to the special characteristics of the water mass in the bay, especially under the control of the low-salinity Bay of Bengal water at the surface and the Indian equatorial water in the deep ocean, the salinity of seawater shows a monotonic increase with depth. For regional varieties of temperature and salinity structures, as the eddies move westward, the temperature anomaly induced by the eddies increases, the effecting depth of the eddies deepens, and the salinity structures are more affected by inflows. In the north-south direction, the salinity structures of the eddies are associated with the local water masses, which comprise lowsalinity water in the northern bay due to the inflow of freshwater from rivers and salty water in the southern bay due to the invasion of Arabian Sea high-salinity water from the north Indian Ocean. 相似文献
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《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(11-12):2371-2403
Statistics of the near-surface circulation in the northeast Pacific Ocean were derived from the trajectories of nearly 100 surface drifters tracked between August 1990 and December 1995 as part of the World Ocean Circulation Experiment's (WOCE) Surface Velocity Program (SVP). Drifters were drogued within the mixed layer (15 m drogue depth) or near the top of the permanent halocline (120 m). All branches of the Alaskan Gyre were well-sampled at both depths, revealing a weak Subarctic Current, a bifurcation of the Subarctic Current near 48°N, 130°W at 15 m depth, and strong, variable flow in the Alaska Current and Alaskan Stream. At 120 m depth, northward flow in the Alaska Current occurred much farther offshore than within the mixed layer. The drifter trajectories revealed interannual variability, with evidence of an intensified Alaskan Gyre during the winters of 1991–92 and 1992–93 and more southerly transport during winter 1994–95. A minimum in eddy kinetic energy was found at both depths within the northern branch of the Subtropical Gyre. Eddy kinetic energies were nearly twice as high in the mixed layer compared to below, and were 2–3 times larger in winter than in summer throughout most of the near-surface Alaskan Gyre. High eddy energies observed near the eastern perimeter of the Alaskan Gyre may be due to the offshore intrusion of eddies formed by coastal current instabilities.Taylor's theory of single-particle dispersion was applied to the drifter ensembles to estimate Lagrangian decorrelation scales and eddy diffusivities. Both the initial dispersion and random walk regimes were identified in the dispersion time series computed for several regions of both ensembles. The integral time scales and eddy diffusivities computed from the dispersion scale linearly with r.m.s. velocity, which is consistent with drifter studies from the Atlantic. An exception is the meridional integral time scales, which were nearly constant throughout the study area and at both drogue depths. The magnitudes of the derived eddy statistics are comparable to those derived from surface drifters in other parts of the world ocean. These are the first Lagrangian estimates of particle dispersion over a broad region of the near-surface North Pacific, and the consistency of the results with previous studies from the Atlantic lends credence to the idea that the simplifying assumptions of Taylor (1921) (Proceedings of the London Mathematical Society Series A 20, 196–221) are reasonably valid throughout the upper ocean. This bodes well for the effective parameterization of near-surface diffusivities in general circulation models. Finally, the drifter-derived velocity statistics were used to speculate on the source regions of waters of possible coastal origin observed at offshore stations during the field studies of the Canadian Joint Global Ocean Flux Study. 相似文献
20.
黑潮是北太平洋副热带环流系统的一支重要的西边界流。前人对不同流段黑潮的季节和年际变化进行了诸多研究,然而基于不同数据所得结论仍存在差异,尤其是不同模式计算所得流量差别很大,而且以往研究往往着眼于某一流段,对不同流段黑潮变化之间的异同及其原因涉及较少。本文基于卫星高度计数据,评估了OFES(Ocean generalcir culation model For the Earth Simulator)和HYCOM(Hybrid Coordinate Ocean Model)两个模式对吕宋岛和台湾岛以东黑潮季节与年际变化的模拟能力,进而对两个海域黑潮变化的异同及其物理机制进行了分析。结果表明:HYCOM模式对黑潮季节变化的模拟较好,而OFES模式对黑潮年际变化的模拟较好。吕宋岛以东黑潮和台湾岛以东黑潮在季节与年际尺度上的变化规律均不相同,且受不同动力过程控制。吕宋岛以东黑潮呈现冬春季强而秋季弱的变化规律,主要受北赤道流分叉南北移动的影响;而台湾岛以东黑潮呈现夏季强冬季弱的变化特点,主要受该海区反气旋涡与气旋涡相对数目的季节变化影响。在年际尺度上,吕宋岛以东黑潮与北赤道流分叉及风应力旋度呈负相关,当风应力旋度超前于流量4个月时相关系数达到了-0.56;而台湾岛以东黑潮的流量变化则受制于副热带逆流区涡动能的变化,且滞后于涡动能9个月时达到最大正相关,相关系数为0.44。本研究对于深入理解不同流段黑潮的多尺度变异规律及其对邻近海区环流与气候的影响具有重要意义,同时对于黑潮研究的数值模式选取具有重要参考价值。 相似文献