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1.
The adjustment of the North Pacific Subtropical and Subpolar Gyres towards changes in wind stress leads to different time-scale variabilities, which plays a significant role in climate changes. Based on the Simple Ocean Data Assimilation (SODA) and Global Ocean Data Assimilation System (GODAS) datasets, the variations of the Subtropical and Subpolar Gyres are diagnosed using "three-dimension Ocean Circulation Diagnostic Method", and established three types of index series describe the strength, meridional and depth center of the Subtropical and Subpolar Gyres. The above indices present the seasonal, interannual and interdecadal variabilities of the Subtropical and Subpolar Gyres, which proves well. Both the Gyres are the strongest in winter, but the Subtropical Gyre is the weakest in summer and the Subpolar Gyre is the weakest in autumn. The Subtropical Gyre moves northward from February to March, southward in October, and to the southernmost in around January, while the Subpolar Gyre moves northward in spring, southward in summer, northward again in autumn and reaching the extreme point in winter to the south. The common feature of the interannual and interdecadal variabilities is that the two gyres were weaker and to the north before 1976-1977, while they were stronger and to the south after 1976-1977. The Subpolar Gyre has made a paramount contribution to the variability on interdecadal scales. As is indicated with the Subpolar Gyre strength indices, there was an important shift from weak to strong around 1976-1977, and the correlation coefficient with the North Pacific Decadal Oscillation (PDO) indices was 0.45, which was far better than that between the Subtropical Gyre strength indices and the PDO. Tests show that influenced by small and mesoscale eddies, the magnitude of large-scale gyres strength is strongly dependent on data resolution. But seasonal interannual and interdecadal large-scale variabilities of the two gyres presented with indices is less affected by model resolution.  相似文献   

2.
This study presents an analysis of the CTD data and the turbulent microstructure data collected in 2014, the turbulent mixing environment above the Atlantic Water(AW) around the Chukchi Borderland region is studied.Surface wind becomes more efficient in driving the upper ocean movement along with the rapid decline of sea ice,thus results in a more restless interior of the Arctic Ocean. The turbulent dissipation rate is in the range of4.60×10~(–10)~(–3.31×10~(–9) W/kg with a mean value of 1.33×10~(–9) W/kg, while the diapycnal diffusivity is in the range of1.45×10~(–6)–1.46×10~(–5)m~2/s with a mean value of 4.84×10~(–6) m~2/s in 200–300 m(above the AW). After investigating on the traditional factors(i.e., wind, topography and tides) that may contribute to the turbulent dissipation rate, the results show that the tidal kinetic energy plays a dominating role in the vertical mixing above the AW. Besides, the swing of the Beaufort Gyre(BG) has an impact on the vertical shear of the geostrophic current and may contribute to the regional difference of turbulent mixing. The parameterized method for the double-diffusive convection flux above the AW is validated by the direct turbulent microstructure results.  相似文献   

3.
The ocean general circulation model for the earth simulator(OFES) products is applied to estimate the transports of the Mindanao Current(MC) and the Mindanao undercurrent(MUC) and explore the relation between them on seasonal scale. In general, the MUC is composed of the lower part of the Southern Pacific Tropical Water(SPTW)and Antarctic Intermediate Water(AAIW). While the deep northward core below 1 500 m is regarded as a portion of MUC. Both salinity and potential density restrictions become more reasonable to estimate the transports of MC/MUC as the properties of water mass having been taken into consideration. The climatological annual mean transport of MC is(37.4±5.81)×10~6 m~3/s while that of MUC is(23.92±6.47)×10~6 m~3/s integrated between 26.5 σ_θ and 27.7 σ_θ, and(17.53±5.45)×10~6 m~3/s integrated between 26.5 σ_θ and 27.5 σ_θ in the OFES. The variations of MC and MUC have good positive correlation with each other on the seasonal scale: The MC is stronger in spring and weaker in fall, which corresponds well with the MUC, and the correlation coefficient of them is 0.67 in the OFES.The same variations are also appeared in hybrid coordinate ocean model(HYCOM) results. Two sensitive experiments based on HYCOM are conducted to explore the relation between MC and MUC. The MUC(26.5σ_θ27.7) is strengthening as the MC increases with the enhancement of zonal wind field. It is shown,however, that the main part of the increasement is the deeper northward high potential density water(HPDW),while the AAIW almost remains stable, SPTW decreases, and vice versa.  相似文献   

4.
The structure of the annual-mean shallow meridional overturning circulation(SMOC) in the South China Sea(SCS) and the related water movement are investigated,using simple ocean data assimilation(SODA) outputs.The distinct clockwise SMOC is present above 400 m in the SCS on the climatologically annual-mean scale,which consists of downwelling in the northern SCS,a southward subsurface branch supplying upwelling at around 10°N and a northward surface flow,with a strength of about 1×10~6 m~3/s.The formation mechanisms of its branches are studied separately.The zonal component of the annual-mean wind stress is predominantly westward and causes northward Ekman transport above 50 m.The annual-mean Ekman transport across 18°N is about 1.2×10~6 m~3/s.An annual-mean subduction rate is calculated by estimating the net volume flux entering the thermocline from the mixed layer in a Lagrangian framework.An annual subduction rate of about 0.66×10~6m~3/s is obtained between 17° and 20°N,of which 87% is due to vertical pumping and 13% is due to lateral induction.The subduction rate implies that the subdution contributes significantly to the downwelling branch.The pathways of traced parcels released at the base of the February mixed layer show that after subduction water moves southward to as far as 11°N within the western boundary current before returning northward.The velocity field at the base of mixed layer and a meridional velocity section in winter also confirm that the southward flow in the subsurface layer is mainly by strong western boundary currents.Significant upwelling mainly occurs off the Vietnam coast in the southern SCS.An upper bound for the annual-mean net upwelling rate between 10° and 15°N is 0.7×10~6m~3/s,of which a large portion is contributed by summer upwelling,with both the alongshore component of the southwest wind and its offshore increase causing great upwelling.  相似文献   

5.
The annual subduction rate in the South Indian Ocean was calculated by analyzing Simple Ocean Data Assimilation(SODA) outputs in the period of 1950–2008. The subduction rate census for potential density classes showed a peak corresponding to Indian Ocean subtropical mode water(IOSTMW) in the southwestern part of the South Indian Ocean subtropical gyre. The deeper mixed layer depth, the sharper mixed-layer fronts and the associated relatively faster circulation in the present climatology resulted in a larger lateral induction, which primarily dominants the IOSTMW subduction rate, while with only minor contribution from vertical pumping.Without loss of generality, through careful analysis of the water characteristics in the layer of minimum vertical temperature gradient(LMVTG), the authors suggest that the IOSTMW was identified as a thermostad, with a lateral minimum of low potential vorticity(PV, less than 200×10~(–12) m~(–1)·s~(–1)) and a low d T?dz(less than 1.5°C/(100m)). The IOSTMW within the South Indian Ocean subtropical gyre distributed in the region approximately from25° to 50° E and from 30° to 39°S. Additionally, the average characteristics(temperature, salinity, potential density)of the mode water were estimated about(16.38 ± 0.29)°C,(35.46 ± 0.04),(26.02 ± 0.04) σ_θ over the past 60 years.  相似文献   

6.
Time-series measurements of dissolved inorganic carbon (DIC) and nutrient concentrations were conducted in the northwestern North Pacific from October 2002 to August 2004. Assuming that data obtained in different years represented time-series seasonal data for a single year, vertical distributions of DIC and nutrients showed large seasonal variabilities in the surface layer (∼100 m). Seasonal variabilities in normalized DIC (nDIC) and nitrate concentrations at the sea surface were estimated to be 81–113 μmol kg−1 and 12.7–15.7 μmol kg−1, respectively, in the Western Subarctic Gyre. The variability in nutrients between May and July was generally at least double that in other seasons. In the Western Subarctic Gyre, estimations based on statistical analyses revealed that seasonal new production was 39–61 gC m−2 and tended to be higher in the southwestern regions or coastal regions. The seasonal new productions in the northwestern North Pacific were two or more times higher than in the North Pacific subtropical gyre and the northeastern North Pacific. It is likely that this difference is due to spatial variations in the concentrations of trace metals and the species of phytoplankton present. In addition, from estimations of surface pCO2 it was verified that the Western Subarctic Gyre is a source of atmospheric CO2 between February and May and a sink for CO2 between July and October.  相似文献   

7.
A P - vector method is optimized using the variational data assimilation technique(VDAT). The absolute geostrophic velocity fields in the vicinity of the Luzon Strait (LS) are calculated, the spatial structures and seasonal variations of the absolute geostrophic velocity field are investigated. Our results show that the Kuroshio enters the South China Sea (SCS) in the south and middle of the Luzon Strait and flows out in the north, so the Kuroshio makes a slight clockwise curve in the Luzon Strait, and the curve is strong in winter and weak in summer. During the winter, a westward current appears in the surface, and locates at the west of the Luzon Strait. It is the north part of a cyclonic gyre which exits in the northeast of the SCS; an anti-cyclonic gyre occurs on the intermediate level, and it exits in the northeast of the SCS, and an eastward current exits in the southeast of the anti-cyclonic gyre.  相似文献   

8.
Sea-surface acoustic backscattering measurements at moderate to high frequencies were performed in the shallow water of the south Yellow Sea, using omnidirectional spherical sources and omnidirectional hydrophones. Sea-surface backscattering data for frequencies in the 6–25 k Hz range and wind speeds of(3.0±0.5)and(4.5±1.0) m/s were obtained from two adjacent experimental sites, respectively. Computation of sea-surface backscattering strength using bistatic transducer is described. Finally, we calculated sea-surface backscattering strengths at grazing angles in the range of 16°–85°. We find that the measured backscattering strengths agree reasonably well with those predicted by using second order small-roughness perturbation approximation method with "PM" roughness spectrum for all frequencies at grazing angles ranged from 40° to 80°. The backscattering strengths varied slightly at grazing angles of 16°–40°, and were much stronger than roughness scattering. It is speculated that scattering from bubbles dominates the backscattering strengths at high wind speeds and small grazing angles. At the same frequencies and moderate to high grazing angles, the results show that the backscattering strengths at a wind speed of(4.5±1.0) m/s were approximately 5 d B higher than those at a wind speed of(3.0±0.5) m/s. However, the discrepancies of backscattering strength at low grazing angles were more than 10 d B. Furthermore the backscattering strengths exhibited no significant frequency dependence at 3 m/s wind speed. At a wind speed of 4.5 m/s, the scattering strengths increased at low grazing angles but decreased at high grazing angles with increasing grazing angle.  相似文献   

9.
Wang  Kun  Du  Jing  Liu  Ming  Wu  Jin-hao  Jiang  Heng-zhi  Jin  Sheng  Song  Lun 《中国海洋工程》2019,33(2):185-197
The Bohai Sea is a seasonal icy sea area that has the lowest latitude of any sea experiencing icing in the northern hemisphere, and simulation studies on oil spills during its sea ice period are the key to analyzing winter oil spill accidents. This study applied the three-dimensional free surface to establish a high-resolution hydrodynamic model and simulate tidal distributions in the Bohai Sea. Then, the oil spill model of the open sea area and thermodynamic model were combined to establish a numerical model for the Bohai oil spill during the winter sea ice period. The hydrodynamic model and sea ice growth and melting model were verified, and the parameters were adjusted based on the measured values, which indicate that the numerical model established in this paper is of high accuracy,stability and ubiquity. Finally, after checking the calculations repeatedly, the diffusion coefficient for the Bohai Sea was determined to be 1.0×10~(–7 )m~2/s. It is better that the comprehensive weathering attenuation coefficient is lower than that of a non-winter oil spill, with 1.3×10~(–7 )m~2/s being the most appropriate coefficient. This study can provide the reliable technical support for the operational safety and reduction in losses caused by winter oil spill accidents for the petroleum industry.  相似文献   

10.
In this study, we develop a variable-grid global ocean general circulation model(OGCM) with a fine grid(1/6)°covering the area from 20°S–50°N and from 99°–150°E, and use the model to investigate the isopycnal surface circulation in the South China Sea(SCS). The simulated results show four layer structures in vertical: the surface and subsurface circulation of the SCS are characterized by the monsoon driven circulation, with basin-scaled cyclonic gyre in winter and anti-cyclonic gyre in summer. The intermediate layer circulation is opposite to the upper layer, showing anti-cyclonic gyre in winter but cyclonic gyre in summer. The circulation in the deep layer is much weaker in spring and summer, with the maximum velocity speed below 0.6 cm/s. In fall and winter, the SCS deep layer circulation shows strong east boundary current along the west coast of Philippine with the velocity speed at 1.5 m/s, which flows southward in fall and northward in winter. The results have also revealed a fourlayer vertical structure of water exchange through the Luzon Strait. The dynamics of the intermediate and deep circulation are attributed to the monsoon driving and the Luzon Strait transport forcing.  相似文献   

11.
The subarctic North Pacific is one of the three major high nitrate low chlorophyll (HNLC) regions of the world. The two gyres, the NE and the NW subarctic Pacific gyres dominate this region; the NE subarctic Pacific gyre is also known as the Alaska Gyre. The NE subarctic Pacific has one of the longest time series of any open ocean station, primarily as a result of the biological sampling that began in 1956 on the weathership stationed at Stn P (50°N, 145°W; also known as Ocean Station Papa (OSP)). Sampling along Line P, a transect from the coast (south end of Vancouver Island) out to Stn P has provided valuable information on how various parameters change along this coastal to open ocean gradient. The NW subarctic Pacific gyre has been less well studied than the NE gyre. This review focuses mainly on the NE gyre because of the large and long term data set available, but makes a brief comparison with the NW gyre. The NE gyre has saturating NO3 concentrations all year (winter = about 16 μM and summer = about 8 μM), constantly very low chlorophyll (chl) (usually <0.5 mg m−3) which is dominated by small cells (<5 μm). Primary productivity is low (about 300–600 mg C m−2 d−1 and varies little (2 times) seasonally. Annual primary productivity is 3 to 4 times higher than earlier estimates ranging from 140 to 215 g C m−2 y−1. Iron limits the utilization of nitrate and hence the primary productivity of large cells (especially diatoms) except in the winter when iron and light may be co-limiting. There are observations of episodic increases in chl above 1 mg m−3, suggesting episodic iron inputs, most likely from Asian dust in the spring/early summer, but possibly from horizontal advection from the Alaskan Gyre in summer/early fall. The small cells normally dominate the phytoplankton biomass and productivity, and utilize the ammonium produced by the micrograzers. They do not appear to be Fe-limited, but are controlled by microzooplankton grazers. The NW Subarctic Gyre has higher nutrient concentrations and a shallower summer mixed depth and photic zone than Stn P in the NE gyre. Chl concentrations tend to be higher (0.5 to 1.5 μg L−1) than Stn P, but primary productivity in the summer is similar to Stn P (600 mg C m−2 d−1). There are no seasonal data from this gyre. Iron enrichment experiments in October, resulted in an increase in chl (mainly the centric diatom Thalassiosira sp.) and a draw down of nitrate, suggesting that large phytoplankton are Fe-limited, similar to Stn P.  相似文献   

12.
Euphotic zone plankton production (P) and respiration (R) were determined from the in vitro flux of dissolved oxygen during six latitudinal transects of the Atlantic Ocean, as part of the Atlantic Meridional Transect (AMT) programme. The transects traversed the North and South Atlantic Subtropical Gyres (N gyre, 18–38°N; S gyre, 11–35°S) in April–June and September–November 2003–2005. The route and timing of the cruises enabled the assessment of the seasonal variability of P, R and P/R in the N and S gyres, and the comparison of the previously unsampled N gyre centre with the more frequently sampled eastern edge of the gyre. Mean euphotic zone integrated rates (±SE) were P=63±23 (n=31), R=69±22 (n=30) mmol O2 m−2 d−1 in the N gyre; and P=58±26 (n=30), R=62±24 (n=30) mmol O2 m−2 d−1 in the S gyre. Overall, the N gyre was heterotrophic (R>P) and it was more heterotrophic than the S gyre, but the metabolic balance of both gyres changed with season. Both gyres were net heterotrophic in autumn, and balanced in spring. This seasonal contrast was most pronounced for the S gyre, because it was more autotrophic than the N gyre during spring. This may have arisen from differences in nitrate availability, because spring sampling in the S gyre coincided with periods of deep mixing to the nitracline, more frequently than spring sampling within the N gyre. Our results indicate that the N gyre is less heterotrophic than previous estimates suggested, and that there is an apparent decrease in R from the eastern edge to the centre of the N gyre, possibly indicative of an allochthonous organic carbon source to the east of the gyre.  相似文献   

13.
2012年南海西北陆架冬季水文特征的观测分析   总被引：1，自引：0，他引：1  
本文基于2012年12月南海西北部陆架海区的温盐和流速实测资料，分析了粤西和琼东陆架海区冬季三维温、盐结构和流场特征，给出沿陆架和跨陆架方向的水体和热盐通量。结果表明：（1）在50m以浅，粤西和琼东海区温度均由近岸向外海递增，深层则相反；冬季近岸海区混合层较深，外海密度跃层位于60—120m深度且层结较强，浮力频率大于10–2/s；（2）海流大致沿等深线向西南流动，30m以深流速大小在0.03—0.40m/s之间，且随着深度增加而略有减小；琼东海区100m等深线附近在60m以浅水层观测到水体辐聚并有明显温度锋面存在；（3）沿陆架方向的水体和热盐输送均大于跨陆架方向，其中粤西单位面积沿/跨陆架水体通量平均值为0.13×10–6/0.03×10–6Sv/m2，低于琼东海区的0.91×10–6/0.56×10–6Sv/m2。  相似文献   

14.
Based on monthly mean Simple Ocean Data Assimilation(SODA) products from 1958 to 2007,this study analyzes the seasonal and interannual variability of the North Equatorial Current(NEC) bifurcation latitude and the Indonesian Throughflow(ITF) volume transport. Further,Empirical Mode Decomposition(EMD) method and lag-correlation analysis are employed to reveal the relationships between the NEC bifurcation location,NEC and ITF volume transport and ENSO events. The analysis results of the seasonal variability show that the annual mean location of NEC bifurcation in upper layer occurs at 14.33°N and ITF volume transport has a maximum value in summer,a minimum value in winter and an annual mean transport of 7.75×106 m3/s. The interannual variability analysis indicates that the variability of NEC bifurcation location can be treated as a precursor of El Ni?o. The correlation coefficient between the two reaches the maximum of 0.53 with a time lag of 2 months. The ITF volume transport is positively related with El Ni?o events with a maximum coefficient of 0.60 by 3 months. The NEC bifurcation location is positively correlated with the ITF volume transport with a correlation coefficient of 0.43.  相似文献   

15.
Between 1996 and the mid-2000s the upper waters (200–700 m) of the Rockall Trough became warmer (+0.72 °C), saltier (+0.088) and reduced in nitrate and phosphate (−2.00 µM and −0.14 µM respectively). These changes, out-with calculated errors, can be explained by the varying influence of southern versus subpolar water masses in the basin as the Subpolar Gyre weakened and contracted. Upper water properties strongly correlate with a measure of the strength of the Subpolar Gyre (the first principal component of sea surface height over the Subpolar North Atlantic) prior to the mid-2000s. As the gyre weakens, the upper layers of the trough become warmer (r−0.85), more saline (r−0.86) and reduced in nitrate and phosphate (r+0.81 and r+0.87 respectively). Further the proportion of subpolar waters in the basin decreases from around 50% to less than 20% (r+0. 88). Since the mid−2000s the Subpolar Gyre has been particularly weak. During this period temperatures decreased slightly (−0.21 °C), salinities remained near constant (35.410±0.005) and phosphate levels low and stable (0.68±0.02 µM). These relative lack of changes are thought to be related to the maximum proportion of southern water masses within the Rockall Trough having been reached. Thus the upper water properties are no longer controlled by changes in the relative importance of different water masses in the basin (as prior to the mid-2000s), but rather a different process. We suggest that when the gyre is particularly weak the interannual changes in upper water properties in the Rockall Trough reflect changes in the source properties of the southern water masses. Since the early-2000s the Subpolar Gyre has been weaker than observed since 1992, or modelled since 1960–1970. Hence upper waters within the Rockall Trough may be warmer, saltier and more depleted in nitrate and phosphate than at any time in the last half century.  相似文献   

16.
基于日本气象厅“长风丸”调查船在2002年4～5月航次期间的CTD资料,结合卫星风场资料,采用改进逆方法计算了琉球群岛两侧海域各断面的流速和流量分布,并分析卫星跟踪浮标资料和同期的卫星高度计资料,得出下面一些主要结论:(1)黑潮流速在PN断面上只有一个流核.通过断面PN的净东北向流量约为34.7×106m3/s,此流量包括台湾暖流、东海黑潮和黑潮以东的反气旋涡的流量.(2)黑潮流速在断面TK上有两个流核,通过断面TK净东向的流量为25.6×106m3/s,黑潮通过海峡后流向断面ASUKA.(3)冲绳岛东南海区琉球海流的流量约为8.8×106m3/s,并流向断面AM.(4)奄美大岛以东的北向海流的流量为12.7×106m3/s,并流向断面ASUKA.在断面ASUKA东南部出现一个中尺度反气旋涡,直径约240 km,其流量约为28.5×106m3/s.(5)四国以南黑潮第一层水体基本来源于通过吐噶喇海峡的黑潮,第二、三层水体来自吐噶喇海峡和奄美大岛以东海域的流量大致相当,而第四层的流量则主要来自于奄美大岛以东海域.(6)浮标资料显示,奄美大岛以东的海流部分来自于断面AM以东海区,并通过断面ASUKA.  相似文献   

17.
Hydrographic, geochemical, and direct velocity measurements along two zonal (7.5°N and 4.5°S) and two meridional (35°W and 4°W) lines occupied in January–March, 1993 in the Atlantic are combined in an inverse model to estimate the circulation. At 4.5°S, the Warm Water (potential temperature θ>4.5°C) originating from the South Atlantic enters the equatorial Atlantic, principally at the western boundary, in the thermocline-intensified North Brazil Undercurrent (33±2.7×106 m3 s−1 northward) and in the surface-intensified South Equatorial Current (8×106 m3 s−1 northward) located to the east of the North Brazil Undercurrent. The Ekman transport at 4.5°S is southward (10.7±1.5×106 m3 s−1). At 7.5°N, the Western Boundary Current (WBC) (17.9±2×106 m3 s−1) is weaker than at 4.5°S, and the northward flow of Warm Water in the WBC is complemented by the basin-wide Ekman flow (12.3±1.0×106 m3 s−1), the net contribution of the geostrophic interior flow of Warm Water being southward. The equatorial Ekman divergence drives a conversion of Thermocline Water (24.58⩽σ0<26.75) into Surface Water (σ0<24.58) of 7.5±0.5×106 m3 s−1, mostly occurring west of 35°W. The Deep Water of northern origin flows southward at 7.5°N in an energetic (48±3×106 m3 s−1) Deep Western Boundary Current (DWBC), whose transport is in part compensated by a northward recirculation (21±4.5×106 m3 s−1) in the Guiana Basin. At 4.5°S, the DWBC is much less energetic (27±7×106 m3 s−1 southward) than at 7.5°N. It is in part balanced by a deep northward recirculation east of which alternate circulation patterns suggest the existence of an anticyclonic gyre in the central Brazil Basin and a cyclonic gyre further east. The deep equatorial Atlantic is characterized by a convergence of Lower Deep Water (45.90⩽σ4<45.83), which creates an upward diapycnal transport of 11.0×106 m3 s−1 across σ4=45.83. The amplitude of this diapycnal transport is quite sensitive to the a priori hypotheses made in the inverse model. The amplitude of the meridional overturning cell is estimated to be 22×106 m3 s−1 at 7.5°N and 24×106 m3 s−1 at 4.5°S. Northward heat transports are in the range 1.26–1.50 PW at 7.5°N and 0.97–1.29 PW at 4.5°S with best estimates of 1.35 and 1.09 PW.  相似文献   

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