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海浪破碎对海洋上混合层中湍能量收支的影响 总被引：3，自引：1，他引：2
海浪破碎产生一向下输入的湍动能通量,在近海表处形成一湍流生成明显增加的次层,加强了海洋上混合层中的湍流垂向混合。为了研究海浪破碎对混合层中湍能量收支的影响,文中分析了海浪破碎对海洋上混合层中湍流生成的影响机制,采用垂向一维湍封闭混合模式,通过改变湍动能方程的上边界条件,引入了海浪破碎产生的湍动能通量,并分别对不同风速下海浪破碎的影响进行了数值研究,分析了混合层中湍能量收支的变化。当考虑海浪破碎影响时,近海表次层中的垂直扩散项和耗散项都有显著的增加,该次层中被耗散的湍动能占整个混合层中耗散的总的湍能量的92.0%,比无海浪破碎影响的结果增加了近1倍;由于平均流场切变减小,混合层中的湍流剪切生成减小了3.5%,形成一种存在于湍动能的耗散和垂直扩散之间的局部平衡关系。在该次层以下,局部平衡关系与壁层定律的结论一致,即湍动能的剪切生成与耗散相平衡。研究结果表明,海浪破碎在海表产生的湍动能通量影响了海洋上混合层中的各项湍能量收支间的局部平衡关系。 相似文献
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Observations of turbulence, stratification, and mean current were made using a microstructure profiler and an acoustic Doppler current profiler (ADCP) during four cruises at a central location in the Ariake Sea, under weakly and strongly stratified conditions. Continuous measurements of the dissipation rate of turbulent kinetic energy (TKE), ε, were made. These revealed that frictional bed turbulence with quarterdiurnal variation in the bottom boundary layer (BBL) was one of the most energetic sources of vertical mixing in the sea. Thickness of the BBL was strongly confined by the stable stratification. We investigate a relationship between the BBL height h and the Ozmidov scale. We present a systematic argument that describes the vertical structure and characteristic scales of velocity and turbulence inside the frictional BBL, where the stratification persisted. Considerable deviation of observed vertical shear from the law of the wall indicated a modification of turbulent scales by the stratification. Shear stress calculated from the velocity data using vertical integration of the equation of motion was found to decrease approximately linearly with height. The TKE production rate P, estimated using the shear stress, was highly correlated with the dissipation rate. The buoyancy contribution to TKE balance in the BBL was quantified in terms of the flux Richardson number R f as R f?=?0.12. 相似文献
4.
本文利用Argo表层盐度、OSCAR海流等数据,基于盐度收支方程的平流输送项来阐述海洋平流输送对热带印度洋表层盐度的调整作用;利用淡水输运量计算公式揭示6条关键断面海洋平流输送对表层盐度空间结构的调整机制。结果表明,海洋平流将赤道西印度洋和阿拉伯海的高盐水输送到低盐海域的赤道东印度洋和孟加拉湾、安达曼海;将赤道东印度洋和孟加拉湾、安达曼海的低盐水输送到高盐海域的赤道西印度洋、阿拉伯海以及赤道南印度洋海域,起到了调整印度洋盐度基本平衡的作用。断面淡水输运量的分析结果表明,导致苏门答腊岛西部海域的强降水中心与低盐中心不重合,澳大利亚西部海域的强蒸发中心与高盐中心不重合的主要原因是水平环流所致;夏季,来自赤道西印度洋和阿拉伯海的高盐水在西南季风环流的驱动下,入侵孟加拉湾,是导致孟加拉湾夏季表层盐度较高的主要原因。 相似文献
5.
Hidekazu Yasuda 《Journal of Oceanography》2004,60(3):587-596
The fundamental nature of the mass flux due to the shear effect is examined analytically in a basin with steady and oscillatory
currents to promote a better understanding of the mass transport process in coastal waters. The currents are given from solutions
of the simplified motion equation so as to be consistent with the diffusion equation. The matter concentration used is given
by an analytical solution of the diffusion equation with the settling flux term contained. Mass flux, yielding the depth-averaged
dispersion coefficient, is rather varied vertically in both steady and oscillatory currents. In the oscillatory current with
a Stokes layer in particular, the vertical profile of flux is more complicated and even negative flux is induced near the
basin floor. This negative flux does not necessarily yield a negative value of the vertically averaged dispersion coefficient.
The exact dispersion coefficient given by the flux analysis is realized only in the steady state of the matter concentration
distribution, though we can scarcely observe the steady state in the actual sea. The vertically uniform longitudinal dispersion
coefficient at the stationary stage is shown to be caused from the vertical complexity of mass flux by the action of the vertical
diffusing and the settling flux.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Understanding tidal and mean flow transport mechanisms that maintain the estuarine salt balance against seaward transport by river flow is one of the fundamental questions of estuarine oceanography. Previous salt transport studies have failed to resolve this problem for two principal methodological reasons, in addition to the inherent variability of estuaries. First, salt transport expansions used to represent the salt balance have included a large number of terms that could not be related to any theory of estuarine circulation and whose physical meaning was thus unclear. Second, it has proven difficult to measure small mean velocities in the presence of much larger tidal variations. A new analysis method that expresses Lagrangian scalar property transport in terms of time and space variations of Eulerian variables is much simpler than expansions previously used and yields new insights into estuarine transport processes. This approach (like previous expansions) is valid for narrow systems in which cross-channel transport processes are weak and the ratio of tidal amplitude to mean depth is small. A surface boundary condition is used to eliminate one class of troublesome terms. The equivalence of the tidal-cycle average transport of tidal variations in salinity and the Stokes transport of mean salinity is then employed to show that the vertically integrated tidal flow plays no role in the overall salt balance. That is, seaward transport of salt caused by the river flow can only be balanced by landward transport resulting from correlations between shear and stratification in the mean, tidal and overtide flows. In a hypothetical inviscid estuary, tide and overtide flows would be vertically uniform, and outward fluvial salt transport could only be balanced by shear and stratification in the mean gravitational circulation. In a more realistic example with strong friction, the gravitational circulation would be severely damped, and inward transport could only be accomplished by correlations of shear and stratification in the tide and overtide flows. 相似文献
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《Ocean Modelling》2004,6(2):177-190
Three parameterisations of the vertical mixing of a primitive equation model that uses a geopotential coordinate system are tested against observations in the context of the Antarctic Bottom Water flow through the Romanche Fracture Zone. On an increasing complexity scale, the three parameterisations are a convection algorithm, a vertical diffusivity depending on a Richarson number, and a vertical diffusivity calculated from a turbulent kinetic energy (TKE) equation. The model uses a high vertical and horizontal resolution.It is shown that the convection algorithm does not produce enough vertical mixing compared to observations. This results in the propagation of a too dense water mass in the downstream basin. On the opposite, the Richardson number-dependent algorithm as well as the TKE algorithm produce a mixing comparable to the observations. With these two parameterisations, the main region of intensification of the vertical mixing is located downstream of the main sill that was also described as the major region of turbulence from observations. The mixing length of the TKE parameterisation is consistent with calculation of Thorpe scales from the fine structure of CTD data. Hence, the two successful parameterisations initially designed for the surface mixed layer also give satisfying results for overflows as soon as the hydraulic control and its associated downstream intensified vertical shear are correctly represented in the model. 相似文献
9.
渤海海峡沉积物输运的参数化计算 总被引：1，自引：1，他引：0
本文以2018年冬季渤海海峡两个站位的定点连续观测数据为基础，使用一维参数化方案，计算了观测站位底边界层内的水平悬浮物输运通量以及推移质输运量。在参数化方案中，简化的一维对流扩散方程被用于计算底边界层内的垂向悬浮物浓度。为了验证参数化方案的可靠性，本文基于观测数据对比了两种底剪切应力计算模型、四种临界起动剪切应力计算方法和两种一维对流扩散方程解法。对比结果表明:(1)不同模型计算的底剪切应力结果相近；(2)临界起动剪切应力受到颗粒间黏性作用的影响；(3)一维对流扩散方程的求解过程需要考虑沉积物浓度的分层效应和不同粒级颗粒临界起动剪切应力的差异。基于上述对比结果确定的最优参数化方案，进一步计算了观测站位的沉积物输运量:(1)在有再悬浮的时段，距底5 m内的水平悬浮物通量占全水深悬浮物通量的比例(T01站约为21%，T02站约为17%)显著高于相同层位水通量的占比；(2)依据参数化方案估算的冬季平均的悬浮物通量比忽略底边界层悬浮物浓度垂向变化的传统方法结果高约16%；(3)推移质输运量比悬移质输运量约低两个数量级。 相似文献
10.
Takashi Ichiye 《Journal of Oceanography》1970,26(6):340-353
Scaling of the equations of motion of the Antarctic Circumpolar Current indicates that the Rossby number and the Ekman number
are 10−4 to 10−5 but the vertical Ekman number may reach unity in the bottom boundary layer. The equations of motion are integrated vertically
from the surface to the bottom and averaged over a latitude circle. The resulting equation in the meridional direction is
predominantly geostrophic, whereas the main terms of the equation in the zonal direction are the wind stress and the bottom
stress. When the vertical eddy viscosity near the bottom is of the order of 102cm2/sec, the total zonal transport through the Drake Passage computed from the balance of the wind stress and the bottom stress
equals 260×106m3/sec, the amount determined byReid andNowlin (1970) from observations.
The northward transport reduces the eastward transport corresponding to the wind stress of the westerlies in the A. C. C.
through the Coriolis' term in the vertically integrated equation of motion of the zonal direction. South of the Drake Passage,
such reduction reaches about ten percent of the wind-driven transport mainly due to the peripheral water discharge. North
of the Drake Passage, the northward transport may be generated by the effect of the South American coast which prevents free
eastward movement of the A. C. C., causing a wake to the east. This transport may contribute to a part of the northward transport
of the bottom water postulated byMunk (1966). The effect of the horizontal eddy viscosity in the zonal transport equation is negligible except near the Antarctic
coast, if the eddy viscosity is less than 109cm2/sec. 相似文献
11.
Deanna Wilson-Diaz Arthur J. Mariano Robert H. Evans 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(2):141-165
This study analyzes the heat budget of the Arabian Sea using satellite-derived sea-surface temperature (SST) from 1985 to 1995 along with other data sets. For a better understanding of air–sea interaction, canonical average monthly fields representing the spatial and temporal structure of the various components of the heat balance of the Arabian Sea are constructed from up to 30 years of monthly atmospheric and oceanic data. The SST over the Arabian Sea is not uniform and continually evolves with time. Cooling occurs over most of the basin during November through January and May through July, with the greatest cooling in June and July. Warming occurs over most of the basin during the remainder of the year, with the greatest warming occurring in March and September. Results indicate that the sign of the net heat flux is strongly dependent on the location and month. The effects of net heat flux and penetrative solar radiation strongly influence the change in SST during February and are less important during August and September. Horizontal advection acts to cool the sea surface during the northeast monsoon months. During the southwest monsoon horizontal advection of surface waters warms the SST over approximately the southern half of the basin, while the advection of upwelled water from the Somalia and Oman coasts substantially cools the northern basin. The central Arabian Sea during the southwest monsoon is the only area where the change in SST is balanced by the entrainment and turbulent diffusion at the base of the mixed layer. Agreement between the temporal change in the satellite-derived SST and the change calculated from the conservation of heat equation is surprisingly good given the errors in the measured variables and the bulk formula parameters. Throughout the year, monthly results over half of the basin agree within 3°. Considering that the SST changes between 8° and 12° over the year, this means that our results explain from 62% to 75% of the change in SST over 56% of the Arabian Sea. Two major processes contribute to the discrepancy in the change in SST calculated according to the heat budget equation and the change in SST derived from satellite observations. The first is the effect of the horizontal advection term. The position of the major eddies and currents during the southwest monsoon greatly affects the change in SST due to the large gradient in temperature between the cold upwelled waters along the Somali coast to the warm waters in the interior of the basin. The second major process is the thermocline effect. In areas of shallow mixed-layer depth, high insolation and wind speeds of either less than 3 m/s or greater than 15 m/s, the bulk formulae parameterization of the surface heat fluxes is inappropriate. 相似文献
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上混合中剪切湍流和朗缪尔环流动力特征差异 总被引：1，自引：0，他引：1
LI Guojing WANG Dongxiao CHEN Ju YAO Jinglong ZENG Lili SHU Yeqiang SUI Dandan 《海洋学报(英文版)》2015,34(5):1-11
Large eddy simulation(LES) is used to investigate contrasting dynamic characteristics of shear turbulence(ST)and Langmuir circulation(LC) in the surface mixed layer(SML). ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downwelling jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity Km of LC is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 2ds–3ds(Stokes depth scale) and the lower layer of the SML,respectively. Its value and position change periodically with time. In contrast, maximum Km induced by ST is located in the middle depth of the SML. The turbulent kinetic energy(TKE) generated by LC is larger than that by ST. The differences in vertical distributions of TKE and Km are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear(S2) near the SML base. In addition, the large-scale eddies and S2 induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC. 相似文献
13.
应用 Prandtl混合长理论导得既包含梯度项又包含二阶导数的湍流通量闭合方案 ,并进一步分析了该封闭方案用于湍流扩散方程的数值解行为。分析表明 :(1)扩散项使污染物扩散并趋于空间均匀分布 ,而频散项导致污染物空间分布非均匀 ;(2 )所给出的改进后的一阶湍流封闭方案既可解释标量物质的局地反梯度输送现象又可能使 K理论用于混合层。 相似文献
14.
Past studies have shown that there is a wave-enhanced, near-surface mixed-layer in which the dissipation rate is greater than
that derived from the “law of the wall”. In this study, turbulence in water columns under wind breaking waves is investigated
numerically and analytically. Improved estimations of dissipation rate are parameterized as surface source of turbulent kinetic
energy (TKE) for a more accurate modelling of vertical profile of velocity and TKE in the water column. The simulation results
have been compared with the experimental results obtained by Cheung and Street (1988) and Kitaigorodskii et al. (1983), with good agreement. The results show that the numerical full model can well simulate the near-surface wave-enhanced
layer and suggest that the vertical diffusive coefficients are highly empirical and related to the TKE diffusion, the shear
production and the dissipation. Analytical solutions of TKE are also derived for near surface layer and in deep water respectively.
Near the surface layer, the dissipation rate is assumed to be balanced by the TKE diffusion to obtain the analytical solution;
however, the balance between the dissipation and the shear production is applied at the deep layer. The analytical results
in various layers are compared with that of the full numerical model, which confirms that the wave-enhanced layer near the
surface is a diffusion-dominated region. The influence of the wave energy factor is also examined, which increases the surface
TKE flux with the wave development. Under this region, the water behavior transits to satisfy the classic law of the wall.
Below the transition depth, the shear production dominantly balances the dissipation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
A numerical model is developed for estimation of local scour around a large circular cylinder under vvave action. The model includes wave diffraction around structures, bed shear stress calculation inside the vvave boundary layer and topo-graphical change model. The vvave model is based on the improved Boussinesq equations for varying depth. The vvave boundary layer is calculaled by solving the integrated momentum equation over the boundary layer. The bed shear stress due to streaming, an important factor affecting the sediment transport around a large-scale cylinder, is calculated. The Lagrangian drift velocity is included in calculation of the suspended sediment transport rates. The model is implemented by a finite element method and the results from the present model, which agree well with experimental data, are com-pared vvith those from other methods. 相似文献
16.
黄海冷水团热结构及其环流解析研究 总被引：10，自引：0，他引：10
本文从一般的流体动力学－热力学方程组出发，通过对历史资料的分析，确立了描述黄海冷水团热结构及其环流的非线性控制方程组，得出近似解析解。理论计算结果表明，夏季北黄海冷水团区域存在中心上升边缘下降的气旋式密度环流。 相似文献
17.
Combination of estimated water transport and accurate measurements of total carbon dioxide (TCO2) on a hydrographic section at 58 °N allows the assessment of meridional inorganic carbon transport in the northern North Atlantic Ocean. The transport has been decomposed into contributions from the large-scale baroclinic overturning, the Ekman transport, baroclinic and a barotropic eddy terms, and an estimated contribution of the East Greenland Current. These terms are −0.27 · 106, +0.03 · 106, +0.03 · 106, +0.10 · 106, and +0.05 · 106 mol s−1, respectively, which result in a total southward inorganic carbon transport of only −0.06 · 106 mol s−1. An order of magnitude estimate of the meridional transport of dissolved organic carbon (DOC) has shown that in general this term cannot be ignored in the total carbon flux, this being +0.04 · 106 to +0.16 · 106 mol s−1 at 58 °N. A simple carbon budget has been formulated for the temperate North Atlantic, using our flux estimates as well as those of Brewer et al. (1989). This budget shows that the divergence of the meridional carbon flux, connected with the freshwater balance of the ocean may be of the same order of magnitude as the divergence of the total inorganic carbon flux. For an accurate estimate of the total carbon budget of the ocean it will be necessary to take both the DOC transport and the effects of the freshwater balance into account. 相似文献
18.
A comparison analysis between developed and undeveloped depressions over the South China Sea 总被引：2，自引：0，他引：2
- In this paper, by using two sets of composite data of developed and undeveloped depressions over the South China Sea, we analyze and compare the dynamic structures, the heating fields and the vorticity budget residuals of two different types of depressions. Our conclusions are as follows:The two types of depressions are similar in thermodynamical and dynamical structures. The main differ ences are : in the high layer of developed depression there is a divergence field, with a center near the zero line of vertical wind shear, and over undeveloped depression, the divergence field is weaker and the vertical wind at its center is greater than 5 m s-1. The thermodynamical field of the former is asymmetrical and that of the latter is quasi - symmetrical. As far as the dynamics structure is concerned, the convergence in the lower layer and the difference of divergence between the upper and lower layers of developed depression is three tmies larger than that of undeveloped depression. The upward motion and he 相似文献
19.
基于大涡模拟与被动示踪物模型的人工鱼礁数值研究 总被引：1，自引：0，他引：1
投放人工鱼礁是解决海洋生态环境问题的重要措施之一。通过使用并行大涡模拟模式（the parallelizeda large-eddy simulation model,PALM）及被动示踪物模型模块,研究了不同流速条件（0.1,0.2,0.4和0.6 m/s）下方型人工鱼礁对流场形态、营养盐的抬升作用、和湍流动能收支的影响。研究表明,鱼礁的存在使得其附近垂向速度增大,产生上升流。受到上升流的抬升作用,鱼礁底部的示踪物迅速进入海洋上层,之后遇到鱼礁后方的背涡流,示踪物的抬升受阻,高度逐渐降低。在上升流区域以及背涡流区域的共同影响下,示踪物抬升区域的最大高度与来流流速无关。不同上升流定义对应的上升流区域的高度与来流流速均不相关;上升流区域的最大速度、平均速度与来流流速都成线性增加的关系;然而随着来流流速的增大,不同上升流定义对应的上升流区域面积的变化趋势却完全不同。投放鱼礁后,鱼礁区域底部的混合增强,区域底部的能量被输运至上层。这说明,鱼礁的存在不仅对营养物质具有抬升作用,还能将能量向上输运。 相似文献
20.
Previous studies have shown that the Boussinesq equations can be used to calculate the instantaneous bottom shear stress induced by transient or periodic waves. The bottom friction term occurs as a convolution integral in time in the continuity equation. The exact numerical integration of a convolution integral demands large computational resources, which makes the method less useful for large scale computations. In this paper we explore how the value of the convolution integral can be estimated if we only use the values of the variables in a limited number of time steps, and discuss the accuracy and computational cost of this method. 相似文献