首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The shelfbreak wintertime thermal front in the Northeastern Gulf of Mexico often exhibits meandering, eddy formation and warm-water intrusion. A high level of frontal variability plays an essential role in exchange processes across the shelf. This study examines the impacts of local frontal instability and bottom topography on turbulent heat exchange across the front using the results of two numerical models. Analysis of a series of numerical experiments reveals that the flow is baroclinically unstable. Predicted frontal instability contributes significantly to cross-frontal exchange and accounts for about 35% of the total eddy heat flux. Onshore eddy heat flux has the highest intensity at the frontal position. In addition, eddy activity and heat flux are sensitive to variation of bottom topography. For topographic features and frontal characteristics that are typical of the area, bottom steepness enhances the flux and is nearly proportional to the cross-frontal heat exchange. The study attempts to explain physical mechanisms that drive frontal circulation in the area and to quantify heat transport across the shelf. Estimated heat fluxes can provide important information for climate and ecosystem modeling of the Mississippi Bight.  相似文献   

2.
莫桑比克海峡及其邻近海区是全球海洋潮流和潮能耗散最强的海区之一。文章利用高分辨率通用环流模式对该海区的正压潮流进行模拟, 并对该海区潮能通量和潮能耗散特征进行分析。结果表明, 莫桑比克海峡及其邻近海区的潮波主要是半日分潮占主导地位, 全日分潮可忽略不计, M2分潮形成1个左旋潮波系统和1个右旋潮波系统, S2分潮形成1个左旋潮波系统。莫桑比克海峡和马达加斯加岛南部等绝大数区域的M2和S2半日潮流是逆时针旋转, 在马达加斯加岛顶部等局部区域是顺时针旋转, 而且在海峡通道等复杂地形处潮流流速量级较大。潮能通量矢量主要来自东边界, 大部分潮能通量沿马达加斯岛北部传入莫桑比克海峡区域, 其中经过马达加斯加岛北部和进入莫桑比克海峡的M2 (S2)分潮的潮能通量分别为156.86GW (40.53GW)和148.07GW (36.05GW), S2分潮潮能通量的量级大约为M2分潮的1/5~1/4。底摩擦耗散主要发生莫桑比克海峡和马达加斯加岛南北部, 其中莫桑比克海峡M2 (S2)分潮的底摩擦耗散为1.762GW (0.460GW), 占其底部总耗散的43.74% (39.72%)。  相似文献   

3.
非线性波浪时域计算的三维耦合模型   总被引：3，自引：1，他引：2  
将计算区域Ω划分为内域Ω1和外域Ω2(Ω2=Ω-Ω1),外域控制方程采用改进线性频散特性的二维Boussinesq方程,用预报一校正法数值求解;结构物附近的内域控制方程为三维Navier-Stokes方程,由VOF方法数值求解。通过在外域和内域相匹配的交界面上设置合适的速度和波面边界条件,建立了三维非线性波浪时域计算的耦合模型。模拟试验表明:(1)耦合模型数值波浪水池可以产生稳定的、重复性较好的波动过程;(2)用耦合模型数值波浪水池求解较大浅水区域上的非线性波浪数值计算问题可以取得较高的计算效率,同时又能得出结构物附近的复杂流场。  相似文献   

4.
measurements by a circular array consisting of 18 wave gauges in a large wave tank, directional spectra of wind-generated waves in deep water are systematically determined by using maximum likelihood method The investigations reveal that the angular spreading of the wave energy is consistent with cos2s(θ/2) proposed by Longuet-Higgins et al.(1963, Ocean Wave Spectra, 111-136), if the bimodal distributions of wave energy are not taken into account. Bimodality occurring on higher frequency than peak frequency is too rare to affect our whole resalts. Surprisingly, a much broader directional spreading than that of the field, which is interpreted by the strongly nonlinear energy transfer because of the very young waves in laboratory, is found. The parameter s depends on frequency in the same way as observed by Mitsuyasu et al.(1975, Journal of Physical Oceanography, 5, 750-760) and Hasselmann et al.(1980, Journal of Physical Oceanography, 10, 1264-1280) in the field, and the relationship between the four nondimensional parameters sm, fo, b1 and b2, determining the directional width, and ū10 (corresponding to the inverse of wave age) are given respectively. The observed distributions are found to agree well with the suggestion of Donelan et al.(1985, Philosophical Transaction of Royal Society of London, A315, 509-562) when applied to field waves.  相似文献   

5.
The spectral analyses of moored current velocities in the central Luzon Strait reveal northward (i.e., downstream of the Kuroshio) propagation of a frontal wave with a five-day period, with wave amplitude increasing northward. Estimated from both curve fitting and frequency domain Empirical Orthogonal Function methods, the characteristics of five-day variations have wave speeds ranging from 32 to 40 cm s−1, wavelengths ranging from 130 to 150 km, and e-folding time scales for growth ranging from 0.8 to 3 days. An analytical two-layer model used to explore linear stability characteristics indicates that bottom topography (two meridional ridges) is important for the Kuroshio stability characteristics in the Luzon Strait. In the two-layer model with the two ridges, the flow is stabilized for the long-wave mode but destabilized for the short-wave mode (due to increasing vertical shear in the horizontal velocity). The analytical model produces wavelengths and phase speeds for the most unstable mode which is similar to the observation, but the growth rate is underestimated. However, a spectral numerical model applied with a more realistic stratification and velocity structure does obtain faster growth rates comparable to the observations. Parameter sensitivity tests were conducted using the analytical model. The characteristics of the most unstable mode are most sensitive to the surface front location relative to the bottom topography but not sensitive to varying the density difference and thickness of the upper layer.  相似文献   

6.
Phytoplankton growth rates and mortality rates were experimentally examined at 21 stations during the 2017 spring intermonsoon(April to early May) in the northern and central South China Sea(SCS) using the dilution technique, with emphasis on a comparison between the northern and central SCS areas which had different environmental factors. There had been higher temperature but lower nutrients and chlorophyll a concentrations in the central SCS than those in the northern SCS. The mean rates of phytoplankton growth(μ_0) and microzooplankton grazing(m) were(0.88±0.33) d~(–1) and(0.55±0.22) d~(–1) in the central SCS, and both higher than those in the northern SCS with the values of μ_0((0.81±0.16) d~(–1)) and m((0.30±0.09) d~(–1)), respectively.Phytoplankton growth and microzooplankton grazing rates were significantly coupled in both areas. The microzooplankton grazing impact(m/μ_0) on phytoplankton was also higher in the central SCS(0.63±0.12) than that in the northern SCS(0.37±0.06). The microzooplankton abundance was significantly correlated with temperature in the surface. Temperature might more effectively promote the microzooplankton grazing rate than phytoplankton growth rate, which might contribute to higher m and m/μ_0 in the central SCS. Compared with temperature, nutrients mainly affected the growth rate of phytoplankton. In the nutrient enrichment treatment,the phytoplankton growth rate(μn) was higher than μ_0 in the central SCS, suggesting phytoplankton growth in the central SCS was nutrient limited. The ratio of μ_0/μn was significantly correlated with nutrients concentrations in the both areas, indicating the limitation of nutrients was related to the concentrations of background nutrients in the study stations.  相似文献   

7.
Since mesoscale features like meanders have great importance in nourishing the coastal fisheries, satellite data analyses and a numerical modeling study were carried out for the east coast of India during spring inter-monsoon time (March-May), when biological productivity is high. During this time, the East India Coastal Current (EICC) system appears as a northward flowing western boundary current of a seasonal subtropical gyre in the Bay of Bengal prior to the summer monsoon with a more intense upwelling in the coastal region. A relatively clear sky permits satellite remote sensing of Sea Surface Temperature (SST) and Chlorophyll-a (Chl-a), whose patterns were verified against geostrophic velocity in altimeter data: i.e., phytoplankton grows in colder and nutrient richer water bounded by the seaward meanders. Progression of meanders in the coastal current was revealed and compared with an eddy-resolving Ocean General Circulation Model (OGCM), which is capable of modeling wind-driven general circulation and each stage of the meander growth. The numerical solutions provided the following results, in reasonable agreement with the linear stability theory using a two-and-a-half layer quasi-geostrophic model. Baroclinic instability plays a key role for the meander growth and eddy generation, while meanders in the coastal current are initiated by isolated mesoscale rotations propagating westward. The baroclinically unstable meanders have a wavelength of 500∼700 km, grow in one month and propagate downstream of the coastal current at several kilometers per day. The instability is not strong enough for the meanders to detach an eddy from the western boundary current.  相似文献   

8.
Behavior of warm water flowing into a model ocean with flat bottom filled with cold water is investigated numerically with a three-dimensional level model in a rotating system.The warm water which flows through the southern opening into the ocean is found to progress in two directions. The east front of the warm water progresses along the east coast and reaches the northern opening. And an eastern boundary current associated with this density structure is formed. The west front progresses along the west coast with the speed much less than that of the eastside front. However, the progression of the west front slows down remarkably half way between the southern and northern boundaries due to-effect, and a baroclinic western boundary current system is formed. Unstable waves whose scales are 200–400 km are found in the region of the eastern boundary current and propagate toward the west. These waves seem to be caused by the baroclinic instability.The boundary currents obtained in the present model are considered to represent some characteristics of the Tsushima Current system in the Japan Sea.  相似文献   

9.
The spatial and temporal variability of the acoustic field in the region of a strong coastal shelfbreak front are examined, using the high-resolution environmental data from the 1996-1997 New England shelfbreak PRIMER experiment to provide input to acoustic propagation models. Specifically, the "SeaSoar" undulating conductivity-temperature-depth (CTD) probe across-shelf transects provide 1-km along-track resolution, including the front, during the spring, summer, and winter seasons. These data allow one to study the diurnal and seasonal temporal variation of the acoustic field, as well as the varying spatial structure of the field. Using the RAM parabolic equation code, across-shelf acoustic field structure at 200, 400, and 1000 Hz is studied for various source depths. A number of interesting propagation effects are noted, the most interesting of which are the inhibition of strong acoustic-bottom interaction by the warm shelf water beneath the shelfbreak front and the existence of small-scale ducts near the front, due to offshore transport. Data from the vertical line arrays deployed as part of PRIMER offer partial validation of the predictions made. Specifically, it is seen that the mean received levels are in reasonable accord with propagation calculations made using locally measured bottom properties and the SeaSoar water-column measurements.  相似文献   

10.
Ａｔｈｒｅｅ－ｄｉｍｅｎｓｉｏｎａｌｏｃｅａｎｇｅｎｅｒａｌｃｉｒｃｕｌａｔｉｏｎｍｏｄｅｌｆｏｒｍｅｓｏｓｃａｌｅｅｄｄｉｅｓ──ⅠＭｅａｎｄｅｒｓｉｍｕｌａｔｉｏｎａｎｄｌｉｎｅａｒｇｒｏｗｔｈｒａｔｅ￥ＷａｎｇＪｉａａｎｄＭｏｔｏＩｋｅｄａ（Ｒ...  相似文献   

11.
Historical hydrographic data are used to determine the spatial and seasonal patterns of uncertainty in thermohaline and sound-speed fields in a well-sampled region, the continental shelf and slope in the Middle Atlantic Bight (MAB). Several different historical databases are combined to produce two-dimensional (2-D) plan view and cross-shelf fields of temperature, salinity, and sound speed in two separate regions, the New England shelf and the shelf off Delaware and Maryland. In addition, spatial maps of the sound-speed fields reveal that the maximum variance of the sound speed occurs at the edge of the continental shelf, in the vicinity of the shelfbreak front. The standard deviation of the sound speed was largest during the spring and summer, with magnitudes as large as 14 m/s in a narrow band coinciding with the mean position of the shelfbreak front. During spring the peak in variance was located near the surface outcrop of the front, but during summer the maximum variance was centered at a depth of 30 m, immediately beneath the seasonal thermocline. Comparisons with both synoptic measurements from the Shelfbreak PRIMER experiment as well as moored time series from the Nantucket Shoals Flux Experiment confirm that the shelfbreak front is a "hotspot" of uncertainty (maximum variance), and that the vertical structure of the peak variance is dependent on the presence or absence of the seasonal thermocline  相似文献   

12.
基于物理模型试验，探究畸形波和不规则波作用下浮体系泊张力差异问题。讨论相对波高、相对周期和畸形波参数α1对系泊张力的影响。结果显示:畸形波参数α1和浮体系泊张力显著相关。在α1=2.0～2.83范围内，畸形波作用下迎浪侧系泊张力最大值可达不规则波作用的1.9倍。在相对波高Hs/d=0.032～0.097范围内，畸形波作用下迎浪侧系泊张力最大值显著大于不规则波的作用结果，但畸形波和不规则波对应的1/3值及平均值几乎一致。就相对周期影响而言，迎浪侧系泊张力最大差别出现在谱峰周期Tp0p范围内。频域方面采用小波分析方法讨论畸形波和不规则波作用下浮体系泊张力时频谱特征，两种波浪作用下系泊张力时频特征有显著差别。  相似文献   

13.
Dynamics of western boundary currents in the subtropical and subpolar gyres are studied as a source-sink flow of barotropic fluid by means of numerical integration of the time-dependent non-linear vorticity equation. The bottom topography consists of a continental shelf of uniform slope (120 km wide) parallel to the straight western coast and a flat bottom of uniform depth. The steady solution in the case of low Reynolds number (Re≦100) shows the vorticity balance of the western boundary current between theβ-, diffusion-, and bottom relief terms. The cuspidated flow of the western boundary current in the subpolar gyre is observed as a compensating flow for the subtropical western boundary current separating from the western coast. In the case of Re=350, the zonal current separating from the coast meanders with the wave length of the stationary Rossby waves. It is shown that in the present model the separation of the boundary current is controlled by the planetary vorticity (f) of the fluid particle in the boundary flow, with which the same particle flows out the eastern wall at the corresponding latitude. The decrease of the efflux width increases the intensity of the non-linear overshooting of the boundary current separating from the western coast.  相似文献   

14.
In the present study, we report N_2 fixation rate(~(15)N isotope tracer assay) and the diazotroph community structure(using the molecular method) in the western tropical North Pacific Ocean(WTNP)(13°–20°N, 120°–160°E). Our independent evidence on the basis of both in situ N_2 fixation activity and diazotroph community structure showed the dominance of unicellular N_2 fixation over majority of the WTNP surface waters during the sampling periods.Moreover, a shift in the diazotrophic composition from unicellular cyanobacteria group B-dominated to Trichodesmium spp.-dominated toward the western boundary current(Kuroshio) was also observed in 2013. We hypothesize that nutrient availability may have played a major role in regulating the biogeography of N_2 fixation.In surface waters, volumetric N_2 fixation rate(calculated by nitrogen) ranged between 0.6 and 2.6 nmol/(L·d) and averaged(1.2±0.5) nmol/(L·d), with 10 μm size fraction contributed predominantly(88%±6%) to the total rate between 135°E and 160°E. Depth-integrated N_2 fixation rate over the upper 200 m ranged between 150 μmol/(m~2·d)and 480 μmol/(m~2·d)(average(225±105) μmol/(m~2·d). N_2 fixation can account for 6.2%±3.7% of the depthintegrated primary production, suggesting that N_2 fixation is a significant N source sustaining new and export production in the WTNP. The role of N_2 fixation in biogeochemical cycling in this climate change-vulnerable region calls for further investigations.  相似文献   

15.
We present the results of six dye tracer experiments that measured the mixing and circulation at the shelfbreak front on the New England Shelf. The last three were conducted during the New England Shelfbreak Productivity Experiment (NESPEX) with concurrent isopycnal float deployments. The results are consistent with the Chapman and Lentz [Chapman, D.C., and Lentz, S.J. (1994). Trapping of a coastal density front by the bottom boundary layer. Journal of Physical Oceanography, 24, 1465–1479.] model prediction of the separation and upwelling along the shelfbreak front of bottom boundary layer (BBL) water forced by an Ekman buoyancy flux, but show considerable variability. Cross-shelf velocities at the detachment point are 2–3 × 10−2 m/s. But seaward, over the slope region, dye tagged water was sheared from the main patch into small filaments that upwelled along the front with cross-shelf speeds up to 0.1 m/s. Cross-shelf diffusion was of order 10 m2/s in the mixed bottom layer and 1 m2/s in the interior along the front. Within the stratified front, the mean vertical diffusivity was Kz  4 × 10−6 m2/s. The dispersion of shelfwater in the slope region is effected by turbulent flow with advective speeds exceeding the small scale diffusive mixing. The mean flux of the detached BBL water is sufficient to account for the net loss of shelf water during its transit from Cape Cod to Cape Hatteras.  相似文献   

16.
Utilizing Si, Fe and Mn concentrations within the end-member PACMANUS hydrothermal fluid, Si-Fe-MnH_2 O Pourbaix diagrams were constructed at 300°C and 25°C. The Pourbaix diagrams show that the main Si, Fe and Mn oxides species precipitating from the hydrothermal fluid were Si O_2, Fe(OH)_3, Fe_3(OH)_8, Mn_3O_4, and Mn_2O_3 at 25°C. During mixing of hydrothermal fluid with seawater, Si O_2 precipitated earlier than FeMn-oxyhydroxides because of the lower stability boundary. Then Fe(OH)_2 precipitated first, followed by Fe_3(OH)_8 and Fe(OH)_3, and last, small amounts of Mn_3O_4 and Mn_2O_3 precipitated. Fe(OH)_3 was readily deposited in alkaline solution with little influence by Eh. There were many Si-Fe-Mn-concentric particles in the polished sections of the massive precipitates collected from PACMANUS. In the concentric nucleus and ellipsoid, Si oxides precipitated first before the hydrothermal fluid had mixed with seawater. In the concentric nucleus, after the precipitation of Si oxides, the increase of p H and Eh promoted the precipitation of Mn oxides around the Si oxides. In the large ellipsoid, the precipitation of Fe was divided into two periods. In the early period, increase of p H value of hydrothermal fluid produced by low-temperature convection and an input of a small volume of seawater promoted a small amount of Fe(OH)_3 to precipitate in the Si-rich core. In the late period, after complete mixing with seawater and the resultant fluid was close to neutral or slightly alkaline in p H, Fe(OH)_3 was easily precipitated from the solution and distributed around the Si-rich core.  相似文献   

17.
利用2006年夏季长江口调查数据分析了长江口海域硝酸盐(NO3-)、亚硝酸盐(NO2-)、铵盐(NH4+)大面分布,NO3-浓度呈近岸高、外海低的特征,NO2-和NH4+浓度在上海市排污口位置有高值区并向外扩散。NO3-,NH4+浓度总体上符合咸淡水混合之稀释效应,与盐度的相关系数(r2)分别为0.815,0.255,呈保守行为,而NO2-浓度与盐度的相关性系数为0.074,呈非保守行为。在确定了淡水端元和咸水端元的基础上,做出理论稀释曲线TDL(theoretical dilution line),由于上海市污染物的输入,淡水端元NO3-,NO2-,NH4+浓度不同程度地正偏于TDL,在外海深层水范围内有机颗粒矿化再生亦呈加入态势。对应高溶解氧的盐度羽状峰处,由于真光层初级生产较强,表层NO3-浓度负偏于TDL约1~19μmol/dm3,NO2-,NH4+浓度也存在不同程度的减小。在长江口最大浑浊带附近,由于高浓度悬浮物吸附NH4+而呈现明显的迁出机制。外海表层海水三氮营养盐浓度数据点偏离TDL程度较小,但在底层由于来自上层的有机颗粒耗氧分解而再生出营养盐,使NO3-,NO2-,NH4+浓度数据一般在TDL之上。  相似文献   

18.
In this paper, the method for determining the direction and velocity of internal tide wave is proposed. The main points are as follows: (1) starting with the continuity equation of incompressible fluid and taking the isotherm whose balance position is situated in the middle of the thermocline as the interface of two-layer ocean, one can get an equation of variations of average total current in the lower and upper layers; (2) WTide (Z) in the above-mentioned equation is expressed in first-order approximation; (3) the internal tide waves are treated as wave packets. Thus, one finds out a statistical relation, AΔu BΔv =ζ, which correlates the average shear effect caused by the internal tide wave with the isothermal fluctuation. The direction and velocity of the wave can be drawn from the formulae: (((1=Arctg (A/B), C1=1/(H0(A2 B2)~1/2).The calculated results agree, in the main, fairly well with two sets of observations at station L3.  相似文献   

19.
中国近海生态动力学模型参数敏感性研究   总被引：3，自引：2，他引：1  
In order to develop a coupled basin scale model of ocean circulation and biogeochemical cycling,we present a biogeochemical model including 12 components to study the ecosystem in the China coastal seas(CCS).The formulation of phytoplankton mortality and zooplankton growth are modified according to biological characteristics of CCS.The four sensitivity biological parameters,zooplankton assimilation efficiency rate(ZooAE_N),zooplankton basal metabolism rate(ZooBM),maximum specific growth rate of zooplankton(μ_(20)) and maximum chlorophyll to carbon ratio(Chl2C_m) are obtained in sensitivity experiments for the phytoplankton,and experiments about the parameter μ_(20'),half-saturation for phytoplankton NO_3 uptake(K_(NO_3)) and remineralization rate of small detritusN(SDeRRN) are conducted.The results demonstrate that the biogeochemical model is quite sensitive to the zooplankton grazing parameter when it ranges from 0.1 to 1.2 d~(-1).The K_(NO_3) and SDeRRN also play an important role in determining the nitrogen cycle within certain ranges.The sensitive interval of KNO_3 is from 0.1 to 1.5(mmol/m~3)~(-1),and interval of SEdRRN is from 0.01 and 0.1 d~(-1).The observational data from September 1998 to July 2000 obtained at SEATS station are used to validate the performance of biological model after parameters optimization.The results show that the modified model has a good capacity to reveal the biological process features,and the sensitivity analysis can save computational resources greatly during the model simulation.  相似文献   

20.
Response of the barotropic western boundary current to typhoon passage is investigated by the use of the numerical models described in Part I. Steady states obtained in Part I are chosen as the initial conditions for undisturbed currents. In these models it is assumed that an axially symmetric typhoon (radius = 100 km, maximum wind speed = 27.4 m/sec) moves parallel to the western boundary.For the model with a flat bottom the boundary flow diminishes its strength and broadens its width after the passage of the typhoon offshore. For the model with a continental slope the effect of the typhoon is significantly different depending on the distance of the path of the typhoon from the western boundary. Specifically the north wind on the continental slope causes the formation of cyclonic vortex, which progresses southwards along the slope in the northern hemisphere. Linear theory of continental shelf waves indicates that the phase speed of the propagation of the vortex is 2.4 m/sec. Anomalies of the water level along the coast are also calculated from geostrophic relationships.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号