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1.
Is the small-scale turbulence an exclusive breaking product of oceanic internal waves 总被引：1，自引：1，他引：0
FAN Zhisong 《海洋学报(英文版)》2011,30(6):1-11
On the basis of the theoretical research results by the author and the literature published up to date, the analysis and the justification presented in this paper show that the breaking products of oceanic internal waves are not only turbulence, but also the fine-scale near-inertial internal waves (the oceanic reversible finestructure) for inertial waves and the internal solitary waves for internal tides respectively. It was found that the oceanic reversible finestructure may be induced by the effect of the horizontal component f (f = 2Ωcosφ) of the rotation vector on inertial waves. And a new instability of the theoretical shear and strain spectra due to the effect of f occurs at critical vertical wavenumber β c ≈ 0.1 cpm. It happens when the levels of shear and strain of the reversible finestructure are higher than those of inertial waves, which is induced by the effect of f along an "iso-potential-pycnal" of internal wave. If all breaking products of internal waves are taken into account, the average kinetic energy dissipation rate is an order of magnitude larger than the values of turbulence observed by microstructure measurements. The author’s theoretical research results are basically in agreement with those observed in IWEX, DRIFTER and PATCHEX experiments. An important impersonal fact is that on the mean temporal scale of thermohaline circulation these breaking products of internal waves exist simultaneously with turbulence. Because inertial waves are generated by winds at the surface, and internal tides are generated by strong tide-topography interactions, the analysis and justification in this paper support in principle the abyssal recipes Ⅱ:energetics of tidal and wind mixing by Munk & Wunsch in 1998, in despite of the results of microstructure measurements for the turbulent kinetic energy dissipation rate and the diapycnal turbulent eddy diffusivity. 相似文献
2.
A new three-dimensional numerical model is derived through a wave average on the primitive N-S equations, in which both the＂Coriolis-Stokes forcing＂ and the＂Stokes-Vortex force＂ are considered. Three ideal experiments are run using the new model applied to the Princeton ocean model （POM）. Numerical results show that surface waves play an important role on the mixing of the upper ocean. The mixed layer is enhanced when wave effect is considered in conjunction with small Langmuir numbers. Both surface wave breaking and Stokes production can strengthen the turbulent mixing near the surface. However, the influence of wave breaking is limited to a thin layer, but Stokes drift can affect the whole mixed layer. Furthermore, the vertical mixing coefficients clearly rise in the mixed layer, and the upper ocean mixed layer is deepened especially in the Antarctic Circumpolar Current when the model is applied to global simulations. It indicates that the surface gravity waves are indispensable in enhancing the mixing in the upper ocean, and should be accounted for in ocean general circulation models. 相似文献
3.
Diapycnal mixing is important in oceanic circulation. An inverse method in which a semi-explicit scheme is applied to discretize the one-dimensional temperature diffusion equation is established to estimate the vertical temperature diffusion coefficient based on the observed temperature profiles. The sensitivity of the inverse model in the idealized and actual conditions is tested in detail. It can be found that this inverse model has high feasibility under multiple situations ensuring the stability of the inverse model, and can be considered as an efficient way to estimate the temperature diffusion coefficient in the weak current regions of the ocean. Here, the hydrographic profiles from Argo floats are used to estimate the temporal and spatial distribution of the vertical mixing in the north central Pacific based on this inverse method. It is further found that the vertical mixing in the upper ocean displays a distinct seasonal variation with the amplitude decreasing with depth, and the vertical mixing over rough topography is stronger than that over smooth topography It is suggested that the high-resolution profiles from Argo floats and a more reasonable design of the inverse scheme will serve to understand mixing processes. 相似文献
4.
Oceanic pycnocline depth retrieval from SAR imagery in the existence of solitary internal waves 总被引：2，自引：1，他引：1
Oceanic pycnocline depth is usually inferred from in situ measurements. It is attempted to estimate the depth remotely. As solitary internal waves occur on oceanic pycnocline and propagate along it, it is possible to retrieve the depth indirectly in virtue of the solitary internal waves. A numerical model is presented for retrieving the pycnocline depth from synthetic aperture radar （SAR） images where the solitary internal waves are visible and when ocean waters are fully stratified. This numerical model is constructed by combining the solitary internal wave model and a two-layer ocean model. It is also assumed that the observed groups of solitary internal wave packets on the SAR imagery are generated by local semidiurnal tides. A case study in the East China Sea shows a good agreement with in situ CTD （conductivity-temperature-depth） data. 相似文献
5.
Effect of Langmuir circulation (LC) on upper ocean mixing is investigated by a two-way wave-current coupled model. Themodel is coupled of the ocean circulationmodel ROMS (regional ocean modeling system) to the surface wave model SWAN (simulating waves nearshore) via the model-coupling toolkit. The LC already certified its importance by many one-dimensional (1D) research andmechanismanalysis work. This work focuses on inducing LC’s effect in a three-dimensional (3-D) model and applying it to real field modeling. In ROMS, theMellor-Yamada turbulence closuremixing scheme is modified by including LC’s effect. The SWAN imports bathymetry, free surface and current information fromthe ROMS while exports significant wave parameters to the ROMS for Stokes wave computing every 6 s. This coupled model is applied to the South China Sea (SCS) during September 2008 cruise. The results show that LC increasing turbulence and deepening mixed layer depth (MLD) at order of O (10 m) in most of the areas, especially in the north part of SCS where most of our measurements operated. The coupled model further includes wave breaking which will bringsmore energy into water. When LC works together with wave breaking,more energy is transferred into deep layer and accelerates the MLD deepening. In the north part of the SCS, their effects aremore obvious. This is consistent with big wind event in the area of the Zhujiang River Delta. The shallow water depth as another reasonmakes themeasy to influence the oceanmixing as well. 相似文献
6.
A one-dimensional mixed-layer model, including a Mellor-Yamada level 2.5 turbulence closure scheme, was implemented to investigate the dynamical and thermal structures of the ocean surface mixed layer in the northern South China Sea. The turbulent kinetic energy released through wave breaking was incorporated into the model as a source of energy at the ocean surface, and the influence of the breaking waves on the mixed layer was studied. The numerical simulations show that the simulated SST is overestimated in summer without the breaking waves. However, the cooler SST is simulated when the effect of the breaking waves is considered, the corresponding discrepancy with the observed data decreases up to 20% and the MLD calculated averagely deepens 3.8 m. Owing to the wave-enhanced turbulence mixing in the summertime, the stratification at the bottom of the mixed layer was modified and the temperature gradient spread throughout the whole thermocline compared with the concentrated distribution without wave breaking. 相似文献
7.
Based on the nonlinear model of two-dimensional random sea waves, a statistical distribution of wave surface slope exact to the third order is derived by using the expansion of the characteristic function and direct calculations of each order moment. Based on the distribution of wave surface slope derived in this paper, a whitecap coverage is proposed by using the limit surface slope as a criterion of wave breaking. The whitecap coverage expressed by the model depends on three parameters which can be determined in principle by the linear wave spectrum and three kinds of wave-wave interaction. 相似文献
8.
Effect of Stokes drift on upper ocean mixing 总被引：1，自引：0，他引：1
Stokes drift is the main source of vertical vorticity in the ocean mixed layer. In the ways of Coriolis - Stokes forcing and Langmuir circulations, Stokes drift can substantially affect the whole mixed layer. A modified Mellor-Yamada 2. 5 level turbulence closure model is used to parameterize its effect on upper ocean mixing conventionally. Results show that comparing surface heating with wave breaking, Stokes drift plays the most important role in the entire ocean mixed layer, especially in the subsurface layer. As expected, Stokes drift elevates both the dissipation rate and the turbulence energy in the upper ocean mixing. Also, ilffluence of the surface heating, wave breaking and wind speed on Stokes drift is investigated respectively. Research shows that it is significant and important to assessing the Stokes drift into ocean mixed layer studying. The laboratory observations are supporting numerical experiments quantitatively. 相似文献
9.
An Improved Nearshore Wave Breaking Model Based on the Fully Nonlinear Boussinesq Equations 总被引：1，自引：2，他引：1
This paper aims to propose an improved numerical model for wave breaking in the nearshore region based on the fully nonlinear form of Boussinesq equations. The model uses the k equation turbulence scheme to determine the eddy viscosity in the Boussinesq equations. To calculate the turbulence production term in the equation, a new formula is derived based on the concept of surface roller. By use of this formula, the turbulence production in the one-equation turbulence scheme is directly related to the difference between the water portide velocity and the wave celerity. The model is verified by Hansen and Svendsen‘s experimental data (1979) in terms of wave height and setup and sctdown. The comparison between the model and experimental results of wave height and setup and setdown shows satisfactory agreement. The modeled turbulence energy decreases as waves attenuate in the surf zone. The modeled production term peaks at the breaking point and decreases as waves propagate shoreward. It is also suggested that both convection and diffusion play their important roles in the transport of turbulence energy immediately after wave breaking. When waves approach to the shoreline, the production and dissipation of turbulence energy are almost balanced. By use of the slot technique for the simulation of the movable shoreline boundary, wave ranup in the swash zone is well simulated by the present model. 相似文献
10.
Based mainly on TOGA COARE data, that is, the CI''D data from R/V Xiangyanghong No.5 (Pu et al.,1993),the temperature and current data from the Woods Hole mooring and other deep current data, the layered numerical profiles of buoyancy frequency and mean current components are figured out.A numerical method calculating internal wave dispersion relation without background shear current, used by Fliegel and Hunkins (1975),is improved to be fit for the internal wave equation with mean currents and their second derivatives.The dispersion relations and wave functions of the long crested internal wave progressing in any direction can be calculated inveniently by using the improved method.A comparison between the calculated dispersion relation in the paper and the dispersion relation in GM spectral model of ocean internal waves (Garret and Munk, 1972) is performed.It shows that the mean currents are important to the dispersion relation of internal waves in the western equatorial Pacific Ocean and that the currents make the wave progressing co-directional with (against) the currents stretched (shrink).The influence of the mean currents on dispersion relation is much stronger than that of their second derivatives, but that on wave function is less than that of their second derivatives.The influences on wave functions result in the change of vertical wavenumber, that is, making the wave function stretch or shrink.There exists obvious turning depth but no significant critical layer absorption is found. 相似文献
11.
风生近惯性内波破碎引起的跨等密度面混合在海洋内部混合中起重要作用。然而其参数化对海洋模式的模拟影响仍有待进一步认识。本文给出的是在模块化海洋模式（MOM）中海洋表面边界层以下引入一个考虑风驱动近惯性内波破碎引起的跨等密度面混合参数化方案的研究工作。模拟结果显示，该方案有效改善MOM4模拟的上层1 000 m以上的温盐偏差，特别是在北太平洋和北大西洋的通风地区。数值试验表明，风生近惯性内波破碎有可能是维持海洋通风过程的重要机制之一，它使得海洋通风区的位温变冷，盐度变淡，整层等位密面加深。维持的通风过程使得北太平洋副极地大涡的影响延伸到副热带大涡。从而模拟的北太平洋中层水源头及其副热带大涡东侧的温盐更接近观测实际。同时，模拟的北大西洋经圈翻转环流强度也更为合理。 相似文献
12.
在大洋环流模式中，铅直混合的参数化方法起着关键性的作用。将大洋细结构混合参数化方法首次应用于世界大洋环流模式中。使用中科院大气所(LASG)发展的20层世界大洋环流模式(OGCM)ML20，月平均风场作为强迫场，利用ML20模式在稳定初始状态下运行300a后的计算结果作为本实验进行数值模拟的初始场。该参数化方法对世界大洋环流模式的影响主要表现为：永久性温度跃层的厚度明显变薄；对深层水和底层水的模拟有改进；对南极中层水的模拟比较成功；但是对赤道海区的模拟结果欠佳。 相似文献
13.
海浪破碎对海洋上混合层中湍能量收支的影响 总被引：2，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
14.
海洋是多尺度强迫-耗散系统,机械能主要在大尺度输入,在小尺度耗散。在大、中尺度运动的能量向小尺度湍流传递过程中,内波扮演着重要角色。内波的生成和破碎可打破海洋动力平衡,而在陆架区,内波（主要是内孤立波）的浅化演变与耗散则是驱动湍流混合的关键过程。通过长期的理论、观测与数值模拟研究,目前已认识到内波浅化过程中主要发生如下演变：波形调制、极性转变、裂变、破碎与耗散。相较于直接发生破碎,浅化演变过程中的裂变及其引发的剪切不稳定和对流不稳定是内孤立波在陆架区的主要耗散机制,显著调制陆架区的跃层混合。从能量串级的角度讲,内孤立波浅化裂变为动力不稳定的高频内波是潮能串级的重要通道。本文简要回顾南海北部陆架区内波的研究历史,并着重总结内波在陆架区演变与耗散机制的研究进展。 相似文献
15.
The response time of the large-scale oceanic circulation due to freshwater perturbations is investigated with models of different complexity. A three-dimensional ocean general circulation model (OGCM) and a zonally averaged ocean model are employed. In order to distinguish advection and diffusion from fast baroclinic processes (e.g. waves in the OGCM) a color tracer is injected at the same time and location as the freshwater discharges. In spite of the inability of the zonally averaged model to represent wave processes in a realistic way similarities with the OGCM are found for the propagation patterns of density anomalies and of color tracer. In the OGCM as well as in the zonally averaged model, density anomalies propagate faster than anomalies of a passive color tracer in the case of vertical density stratification. The progression of density anomalies leads to changes of the oceanic circulation, and both oceanic models exhibit circulation changes in areas distant from the discharge places long before the passively entrained color tracer has reached these regions. The fact that a zonally averaged model simulates baroclinic processes faster than advection even if internal gravity waves are not represented due to neglected acceleration terms, is clarified with a conceptual box model. 相似文献
16.
Langmuir环流影响着海洋上层的能量输入,对海洋上混合层的形成和加深起着重要作用,对于海洋上混合层具有重要意义。近年来许多学者采用大涡模拟(LES)方法对Langmuir环流进行机制研究,并通过在雷诺平均模型中参数化Langmuir环流效应,将Langmuir环流过程引入到三维海洋环流或海洋耦合模式中,提出了一系列混合参数化方案。本文回顾了Langmuir环流在雷诺平均模式参数化中的研究进展,主要可分为以下几种方案:一种方法是用Langmuir数在KPP垂直混合参数化方案中引入湍流特征速度增强因子,并不断发展Langmuir数的定义;一种是在Mellor-Yamada2.5湍流闭合模型中增加斯托克斯漂流剪切效应项,此外还有通过修改模式中混合长方程来加入Langmuir效应等。通过在雷诺平均模式中应用的结果来看,现有的参数化方案在一定程度上改善了混合层深度和SST的模拟,肯定了Langmuir环流在加深混合等方面的作用,但仍存在一些问题需要在今后的研究中进一步改进。 相似文献
17.
The turbulent motions responsible for ocean mixing occur on scales much smaller than those resolved in numerical simulations
of oceanic flows. Great progress has been made in understanding the sources of energy for mixing, the mechanisms, and the
rates. On the other hand, we still do not have adequate answers to first order questions such as the extent to which the thermohaline
circulation of the ocean, and hence the earth's climate, is sensitive to the present mixing rates in the ocean interior. Internal
waves, generated by either wind or flow over topography, appear to be the principle cause of mixing. Mean and eddy flows over
topography generate internal lee waves, while tidal flows over topography generate internal tides. The relative importance
of these different internal wave sources is unknown. There are also great uncertainties about the spatial and temporal variation
of mixing. Calculations of internal tide generation are becoming increasingly robust, but we do not know enough about the
subsequent behavior of internal tides and their eventual breakdown into turbulence. It does seem, however, that most internal
tide energy flux is radiated away from generation sites as low modes that propagate over basin scales. The mechanisms of wave-wave
interaction and topographic scattering both act to transfer wave energy from low modes to smaller dissipative scales.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
《Ocean Modelling》2011,39(3-4):267-279
Near-surface enhancement of turbulent mixing and vertical mixing coefficient for temperature owing to the effect of surface wave breaking is investigated using a two-dimensional (2-D) ocean circulation model with a tidal boundary condition in an idealized shelf sea. On the basis of the 2-D simulation, the effect of surface wave breaking on surface boundary layer deepening in the Yellow Sea in summer is studied utilizing a 3-D ocean circulation model. A well-mixed temperature surface layer in the Yellow Sea can be successfully reconstructed when the effect of surface wave breaking is considered. The diagnostic analysis of the turbulent kinetic energy equation shows that turbulent mixing is enhanced greatly in the Yellow Sea in summer by surface wave breaking. In addition, the diagnostic analysis of momentum budget and temperature budget also show that surface wave breaking has an evident contribution to the turbulent mixing in the surface boundary layer. We therefore conclude that surface wave breaking is an important factor in determining the depth of the surface boundary layer of temperature in the Yellow Sea in summer. 相似文献