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1.
Topex/Poseidon (T/P) altimetry has reopened the problem of how tidal dissipation is to be allocated. There is now general agreement of a M2 dissipation by 2.5 Terawatts (1 TW = 1012 W), based on four quite separate astronomic observational programs. Allowing for the bodily tide dissipation of 0.1 TW leaves 2.4 TW for ocean dissipation. The traditional disposal sites since (1920) have been in the turbulent bottom boundary layer (BBL) of marginal seas, and the modern estimate of about 2.1 TW is in this tradition (but the distribution among the shallow seas has changed radically from time to time). Independent estimates of energy flux into the marginal seas are not in good agreement with the BBL estimates.T/P altimetry has contributed to the tidal problem in two important ways. The assimilation of global altimetry into Laplace tidal solutions has led to accurate representations of the global tides, as evidenced by the very close agreement between the astronomic measurements and the computed 2.4 TW working of the Moon on the global ocean. Second, the detection by and (1996) of small surface manifestation of internal tides radiating away from the Hawaiian chain has led to global estimates of 0.2 to 0.4 TW of conversion of surface tides to internal tides. Measurements of ocean microstructure yields 0.2 TW of global dissipation by pelagic turbulence (away from topography). We propose that pelagic turbulence is maintained by topographic scattering of barotropic into baroclinic tidal energy, via internal tides and internal waves. Previous estimates by (1974); , (1982)) of this conversion along 150,000 km of continental coastlines gave a negligible 0.02 TW; evidently the important conversion takes place along mid-ocean ridges.The maintenance of the abyssal global stratification requires a much larger expenditure of power. 2 TW versus 0.2 TW. This is usually attributed to wind forcing. If tidal power is to play a significant role here, then the BBL estimates need to be reduced. The challenge is to estimate dissipation from the energy flux divergence in the T/P adjusted tidal models, without prior assumptions concerning the dissipation processes.  相似文献   

2.
Progress in tidal science has been rapid in recent years. The advent of precision altimetry has enabled, for the very first time in tidal history, an accurate measurement of tides in most of the global oceans. This has revolutionized our knowledge of tides and tidal processes. Combined with high‐resolution numerical models of tides (and other recent advances in astronomy and geodesy), this increased knowledge is providing valuable assistance in effecting closure on many outstanding problems in this three‐centuries‐old science. For example, we now know the dissipation rate of lunar tides to be 3.17 TW to within 2%. However, there do remain some outstanding issues. While we know the rate at which tidal energy is being dissipated in the global oceans, there is still considerable uncertainty as to the mechanisms, locations, and magnitudes of various tidal energy sinks. Imminent advances in shallow‐water barotropic and deep‐water baroclinic tides hold the prospect of a better understanding of these also. Improved knowledge of oceanic tides and high‐precision satellite measurements of tides are enabling better assessment of some matters of geophysical interest, such as the anelasticity and the length‐of‐day fluctuations of the Earth's mantle. It has been possible to map long‐period lunar tides more accurately and derive their contribution to the Earth's rotation rate fluctuations and its anelasticity at these frequencies. We discuss various aspects related to tides, including tidal dissipation and its consequences, as well as several other topics such as tidal energetics, internal tides, and long‐period tides, where considerable progress has been made in the last decade. Both oceanographic and geophysical implications are mentioned.  相似文献   

3.
A three-dimensional isopycnic-coordinate internal tidal model is employed to investigate the generation,propagation, vertical structure and energy conversion of M2 internal tides in the Luzon Strait(LS) with mooring observations. Simulated results, especially the tidal current amplitudes, agree well with observations,demonstrating the reasonability and accuracy of the model. Results indicate that M2 internal tides mainly propagate into three directions horizontally, i.e., eastward towards the western Pacific Ocean, westward towards the Dongsha Island and southwestward towards the South China Sea Basin. In the horizontal direction, tidal current amplitudes decrease as distance increases away from the LS; in the vertical direction, they show an obvious decreasing tendency with depth. Between the double ridges of the LS, a clockwise gyre of M2 baroclinic energy flux appears, which is caused by reflections of M2 internal tides at supercritical topographies, and resonance of M2 internal tides happens along 19.5° and 21.5°N due to the heights and separation distance of the double ridges. The total energy conversion in the LS is about 14.20 GW.  相似文献   

4.
Numerical study of baroclinic tides in Luzon Strait   总被引：6，自引：1，他引：5  
The spatial and temporal variations of baroclinic tides in the Luzon Strait (LS) are investigated using a three-dimensional tide model driven by four principal constituents, O1, K1, M2 and S2, individually or together with seasonal mean summer or winter stratifications as the initial field. Barotropic tides propagate predominantly westward from the Pacific Ocean, impinge on two prominent north-south running submarine ridges in LS, and generate strong baroclinic tides propagating into both the South China Sea (SCS) and the Pacific Ocean. Strong baroclinic tides, ∼19 GW for diurnal tides and ∼11 GW for semidiurnal tides, are excited on both the east ridge (70%) and the west ridge (30%). The barotropic to baroclinic energy conversion rate reaches 30% for diurnal tides and ∼20% for semidiurnal tides. Diurnal (O1 and K1) and semidiurnal (M2) baroclinic tides have a comparable depth-integrated energy flux 10–20 kW m−1 emanating from the LS into the SCS and the Pacific basin. The spring-neap averaged, meridionally integrated baroclinic tidal energy flux is ∼7 GW into the SCS and ∼6 GW into the Pacific Ocean, representing one of the strongest baroclinic tidal energy flux regimes in the World Ocean. About 18 GW of baroclinic tidal energy, ∼50% of that generated in the LS, is lost locally, which is more than five times that estimated in the vicinity of the Hawaiian ridge. The strong westward-propagating semidiurnal baroclinic tidal energy flux is likely the energy source for the large-amplitude nonlinear internal waves found in the SCS. The baroclinic tidal energy generation, energy fluxes, and energy dissipation rates in the spring tide are about five times those in the neap tide; while there is no significant seasonal variation of energetics, but the propagation speed of baroclinic tide is about 10% faster in summer than in winter. Within the LS, the average turbulence kinetic energy dissipation rate is O(10−7) W kg− 1 and the turbulence diffusivity is O(10−3) m2s−1, a factor of 100 greater than those in the typical open ocean. This strong turbulence mixing induced by the baroclinic tidal energy dissipation exists in the main path of the Kuroshio and is important in mixing the Pacific Ocean, Kuroshio, and the SCS waters.  相似文献   

5.
吐噶喇海峡是西北太平洋重要的内潮产生区域,该区域内产生的内潮对于东海陆架和西北太平洋的混合和物质输运有十分重要的作用。水平分辨率为3km的JCOPE-T(JapanCoastalOcean PredictabilityExperiment—Tides)水动力学模式的结果表明,吐噶喇海峡的内潮主要产生在地形变化剧烈的海山和海岛附近,其引起的等密面起伏振幅可达30m。吐噶喇海峡的内潮在垂直于等深线方向分为两支向外传播:一支向西北方向传播,进入东海陆架后迅速减小;另一支向东南方向传播,进入西北太平洋。吐噶喇海峡潮能丰富,其在约半个月内的平均输入的净正压潮能通量为13.92GW,其中约有3.73GW转化为内潮能量。生成的内潮能量有77.2%在当地耗散,传出的内潮能通量为0.84GW,主要通过西北和东南两个边界传出。该区域潮能通量有显著的大小潮变化,大潮期间输入的正压潮净能通量和产生的内潮能通量均约为小潮期间的2倍,但其主要产生区域基本不变,且内潮能量耗散比率均在产生的内潮通量的76%—79%。另外,内潮能通量的传播方向也没有发生变化,仍主要通过西北和东南两个边界传出。因此,大小潮的变化仅影响吐噶喇海峡处产生的内潮能量的大小,不影响其产生区域、传播方向和耗散比率。  相似文献   

6.
Sub‐gridscale processes take place throughout the global atmosphere. Yet they have been neglected in traditional estimates of the global energy cycle on the ground that they can be treated as molecular heat fluxes. This view may cause quantitative underestimates of the efficiency of the global circulation of the atmosphere. In Part I of this two-part study we revisit the classical theory, beginning with the local energy equations. Similar to Lorenz we introduce a barotropic reference pressure p r and define a generalized field equation for the integrand of available potential energy, without reference to hydrostasy. The emerging energy quantity is new in that it comprises not only the classical correlation between efficiency factor and enthalpy but also an additional potential that depends upon p r . We then perform mass-averaging over the scale of contemporaneous global models (40‐400 km) and come up with averaged field energy equations, valid at the gridscale. Additional global and time-averaging of these removes all divergences and tendencies and yields two equations for the global energy reservoirs. The available potential energy reservoir is fed by gridscale plus sub-gridscale generation. The kinetic energy reservoir is tapped by gridscale plus sub-gridscale dissipation. Exchange between the reservoirs is carried by both gridscale and sub-gridscale conversion terms ( C grid, C sub ). Generation, conversion and dissipation fluxes are complete, as compared to the approximate quantities in the traditional formulation of the energy cycle. This approach allows to fully exploit Lorenz's original concept. The gridscale equations derived will be the basis for evaluating numerically the classical Lorenz terms plus a couple of new global conversion fluxes, notably C sub, to be presented in Part II of this study.  相似文献   

7.
文章采用三维海洋模式MITgcm, 对印度尼西亚海(简称印尼海)内潮的生成和传播过程进行了研究。研究结果表明: 1)苏拉威西海和西北太平洋地区的内潮呈现明显的全日潮信号; 望加锡海峡、翁拜海峡、东北印度洋、帝汶海等站位的内潮呈现明显的半日潮信号; 2)印尼海区内潮的标准化振幅在苏拉威西海、望加锡海峡、翁拜海峡、马鲁古海、班达海、东北印度洋和西北太平洋地区均在温跃层附近达到最大, 约为20~40m; 在帝汶海地区在水深200m附近达到最大, 约为25~30m; 3)桑岭、斯兰海、翁拜海峡和帝汶海是主要的内潮生成区域, 内潮能通量达40kW·m-1; 4)苏禄海的内潮能量主要来自于局地正压潮的转化, 苏拉威西海和班达海的内潮能量则主要来自外部的传入。  相似文献   

8.
内潮耗散与自吸-负荷潮对南海潮波影响的数值研究   总被引：1，自引：0，他引：1  
利用非结构三角形网格的FVCOM海洋数值模式,在其传统二维潮波方程中加入参数化的内潮耗散项和自吸-负荷潮项,计算了南海及其周边海域的M_2、S_2、K_1和O_1分潮的分布。与实测值的比较表明,引入这两项对模拟准确度的提高有明显效果。根据模式结果本文计算分析了研究海域的潮能输入和耗散。能量输入计算表明,能通量是潮能输入的最主要构成部分,通过吕宋海峡断面进入南海的M_2和K_1分潮能通量分别为38和29GW;半日周期的自吸-负荷潮能量输入以负值居多,而全日周期的自吸-负荷潮能量输入以正值居多,因而自吸-负荷潮减弱了南海的半日潮,并加强了南海的全日潮。引潮力的作用也减弱了半日潮而加强了全日潮,但其作用要小于自吸-负荷潮。潮能耗散的分析显示底摩擦耗散在沿岸浅水区域起主导作用,内潮耗散则主要发生在深水区域。内潮耗散的最大值出现在吕宋海峡,且位于南海之外的海峡东部的耗散量大于位于南海之内的海峡西部的耗散量。对M_2和K_1分潮吕宋海峡的内潮耗散总值分别达到16和23GW。  相似文献   

9.
Seasonal variations of baroclinic tides for K1 and M2 constituents were separately studied using two-dimensional numerical simulations along the 21°N section of the northern South China Sea (SCS). Results show that the continental slope of the northern SCS and the west ridge of the Luzon Strait are supercritical to K1 internal tides, which may be trapped in the deep basin of the SCS and form standing or partial standing waves. Meanwhile, these areas are sub-critical to M2 internal tides, which can transmit onto the shelf and are seldom reflected back into the basin. The trapped K1 internal tides are dominated by mode-2 and mode-3 in summer and by mode-1 and mode-3 in winter. Moreover, high mode K1 internal tides account for nearly 20–40 % of the total energy density in winter and 15–20 % in summer. The pattern of K1 internal tides in the basin is mainly determined by the percentage of reflected energy from the continental slope. The phase difference between the incoming mode-1 and mode-2 K1 internal tides near the continental slope are nearly out of phase in winter, which means that the percentage of reflection of the K1 internal tide is larger than that in summer. Both the convergence and high mode K1 internal tides can enhance the vertical shear. The above results indicate that, in the deep basin of the SCS, water mixing potentially induced by internal tides in winter is stronger than in summer.  相似文献   

10.
多波束水深测量中受潮汐因素的影响,测量垂直基准是变化的,具有瞬时性。传统多波束测量,需在测区内设立一个或多个验潮站进行同步水位观测,最终将水深归算到深度基准面上。针对多波束水深测量中垂直基准转换的复杂性问题,文中基于地球重力场模型,结合测区内实测的GNSS/水准数据,通过插值算法建立了测区范围内似大地水准面精化模型,构建了多波束无验潮水深测量的垂直基准转换模型。通过实例表明,该方法有效地消除了潮汐、动态吃水及涌浪等因素影响,直接获取深度基准面的水深值,提高工作效率,可满足近岸多波束水深测量的工作需求。  相似文献   

11.
Time series of temperature and salinity collected from a station in the NE Arabian Sea during March, April, May, October, and November was utilized to explain the behavior of internal tides. Analysis revealed the existence of semi-diurnal internal tides and high frequency (HF) internal waves (IW). It was observed that the amplitudes of HF IWs were determined by the degree of stratification in the thermocline. Corresponding to an increase in the density gradient in thermocline (0.016 kg/m4 in April to 0.14 kg/m4 in October), the temperature fluctuations due to internal tides increased from <0.2°C to >1.5°C, respectively. Brunt-Vaiisala frequency also showed similar variations (～10 cph to 22 cph). Within the thermocline, semi-diurnal internal tides caused fluctuations of >10m in the isotherm depths. A linear regression equation was fitted to parameterize the amplitude of HF IWs and its upper frequency limit in terms of thermocline gradient. The IW and one-dimensional models simulated the presence of internal tides and diurnal cycling in the temperature field, respectively. Coupling of these models showed improvement in the simulation of temperature.  相似文献   

12.
Process-based numerical modelling of coastal morphodynamics involves model and data reduction schemes in order to cope with computational limitations. Model reduction, on the one hand, may involve the discretisation of an interactive multidimensional, diverse natural system into a reduced set of coupled process-simulation modules. Data reduction schemes, on the other hand, are used to parameterise processes. The use of schematised open-boundary conditions, which are considered as representative in terms of their cumulative morphological effect, is based on the concept of “morphological” or “representative” boundary conditions. Recent model applications show realistic tendencies in terms of depositional and erosional areas. By contrast, the reproduction of characteristic changes in morphology such as the migration of bars, banks and channels is only occasionally achieved. Using field data on observed morphological impact of a single storm event and numerical model data, it is demonstrated that the concept of representative tides may lead to simulations of morphological development lacking natural dynamics. It is proposed that rather than being based on “representative” single tides, morphodynamic models should be applied with open-boundary conditions which take variations in longer-term tidal and meteorological forcing into account.  相似文献   

13.
《Ocean Modelling》2010,35(3-4):125-136
This paper seeks to illustrate the point that physical inconsistencies between thermodynamics and dynamics usually introduce nonconservative production/destruction terms in the local total energy balance equation in numerical ocean general circulation models (OGCMs). Such terms potentially give rise to undesirable forces and/or diabatic terms in the momentum and thermodynamic equations, respectively, which could explain some of the observed errors in simulated ocean currents and water masses. In this paper, a theoretical framework is developed to provide a practical method to determine such nonconservative terms, which is illustrated in the context of a relatively simple form of the hydrostatic Boussinesq primitive equation used in early versions of OGCMs, for which at least four main potential sources of energy nonconservation are identified; they arise from: (1) the “hanging” kinetic energy dissipation term; (2) assuming potential or conservative temperature to be a conservative quantity; (3) the interaction of the Boussinesq approximation with the parameterizations of turbulent mixing of temperature and salinity; (4) some adiabatic compressibility effects due to the Boussinesq approximation. In practice, OGCMs also possess spurious numerical energy sources and sinks, but they are not explicitly addressed here.Apart from (1), the identified nonconservative energy sources/sinks are not sign definite, allowing for possible widespread cancellation when integrated globally. Locally, however, these terms may be of the same order of magnitude as actual energy conversion terms thought to occur in the oceans. Although the actual impact of these nonconservative energy terms on the overall accuracy and physical realism of the oceans is difficult to ascertain, an important issue is whether they could impact on transient simulations, and on the transition toward different circulation regimes associated with a significant reorganization of the different energy reservoirs. Some possible solutions for improvement are examined. It is thus found that the term (2) can be substantially reduced by at least one order of magnitude by using conservative temperature instead of potential temperature. Using the anelastic approximation, however, which was initially thought as a possible way to greatly improve the accuracy of the energy budget, would only marginally reduce the term (4) with no impact on the terms (1), (2) and (3).  相似文献   

14.
Luni-solar tides affect Earth's rotation in a variety of ways. We give an overview of the physics and focus on the excitation of Earth rotational variations by ocean tides under the conservation of angular momentum. Various models for diurnal and semidiurnal tidal height and tidal current fields have been derived, following a legacy of a number of theoretical tide models, from the Topex/Poseidon (T/P) ocean altimetry data. We review the oceanic tidal angular momenta (OTAM) predicted by these T/P models for the eight major tides (Q1, O1, P1, K1, N2, M2, S2, K2), and their excitations on both Earth's rotational speed variation (in terms of length-of-day or UT1) and polar motion (prograde diurnal/semidiurnal components and retrograde semidiurnal components). These small, high-frequency effects have been unambiguously observed in recent years by precise Earth rotation measurements via space geodetic techniques. Here we review the comparison of the very-long-baseline-interferometry (VLBI) data with the T/P OTAM predictions. The agreement is good with discrepancies typically within 1 – 2 microseconds for UT1 and 10 – 30 microarcseconds for polar motion. The eight tides collectively explain the majority of subdaily Earth rotation variance during the intensive VLBI campaign Cont94. This establishes the dominant role of OTAM in exciting the diurnal/semidiurnal polar motion and paves the way for detailed studies of short-period non-OTAM excitations, such as atmospheric and oceanic angular momentum variations, earthquakes, the atmospheric thermal tides, Earth librations, and the response of the mantle lateral inhomogeneities to tidal forcing. These studies await further improvements in tide models and Earth rotation measurements.  相似文献   

15.
The generation of internal waves from barotropic tides can be quantified in terms of the conversion rates. These have often been obtained by applying the WKB approximation, which yields an expression for the conversion rates which is proportional to the seabed buoyancy frequency   N B   . For small values of   N B   or strong variations of the buoyancy profile   N ( z )  , this gives unreliable results. Using homogenization theory it is here shown that the conversion rate instead depends on the value of   N ( z )  averaged over a vertical region at the bottom of the same magnitude as the vertical length-scale of the internal wave, which for the lowest modes is of the same order as the entire ocean depth. This gives a substantially larger conversion rate.  相似文献   

16.
The global distributions of the major semidiurnal (M2 and S2) and diurnal (K1 and O1) baroclinic tide energy are investigated using a hydrostatic sigma-coordinate numerical model. A series of numerical simulations using various horizontal grid spacings of 1/15–1/5° shows that generation of energetic baroclinic tides is restricted over representative prominent topographic features. For example, nearly half of the diurnal (K1 and O1) baroclinic tide energy is excited along the western boundary of the North Pacific from the Aleutian Islands down to the Indonesian Archipelago. It is also found that the rate of energy conversion from the barotropic to baroclinic tides is very sensitive to the horizontal grid spacing as well as the resolution of the model bottom topography; the conversion rate integrated over the global ocean increases exponentially as the model grid spacing is reduced. Extrapolating the calculated results in the limit of zero grid spacing yields the estimate of the global conversion rate to be 1105 GW (821, 145, 102, 53 GW for M2, S2, K1, and O1 tidal constituents, respectively). The amount of baroclinic tide energy dissipated in the open ocean below a depth of 1000 m, in particular, is estimated to be 500–600 GW, which is comparable to the mixing energy estimated by Webb and Suginohara (Nature 409:37, 2001) as needed to sustain the global overturning circulation.  相似文献   

17.
杜涛  方欣华 《海洋预报》1999,16(4):26-32
提出根据内潮数值模式所要解决的主要问题进行分类的方法,将现有内潮数值模式分为三 种类型：生成模式、传播模式和统一模式。生成模式主要研究在表面潮与地形的相互作用下内 潮在层化海水中的产生过程,传播模式研究内潮生成后的传播过程,统一模式则将生成和传播 过程一起研究。分别介绍了近年来最新的各类模式和大部分早期模式的主要组成部分和特征, 指出内潮模式发展需要解决的问题和发展方向。  相似文献   

18.
Tides are believed to drive vertical mixing in the Arctic Ocean, thereby helping heat to reach the bottom of the sea ice layer, especially in regions with thick ice covers. However, tides are usually not included in ocean models. We investigated the effect of tides on sea ice in the Arctic Ocean using an ice-coupled ocean model that includes tides simultaneously. We found that with tidal forcing, the volume of sea ice increased by 8.5% in Baffin Bay, whereas it decreased by 17.8% in the Canadian Arctic Archipelago. The increase in sea ice volume in Baffin Bay results from the convergence of sea ice, driven by tidal residual currents. In contrast, the decrease in ice volume in the Canadian Archipelago is due to the suppression of ice formation in winter, especially in areas with steep topography, where the vertical mixing of temperature is enhanced by tides. Our results imply that tides should be directly included into the oceanic general circulation model (OGCM) to realistically reproduce the distribution of sea ice in the Arctic Ocean.  相似文献   

19.
对1998年6月南海北部20天的海流和温度定点连续观测资料进行分析,得到该海域内潮的特征及其能量分布。分析结果显示内潮的主要成分为O1,K1,M2与S2分量,其中全日内潮（O1与K1）的能量占主要部分。在观测期间,此四个分量的海流失量均为顺时针旋转,其潮流椭圆半长轴的最大值超过14cm/s。海水温度的变化显示出内潮存在准日周期振动,平均垂向振幅达到50m。观测到的内潮携带高能量且其活动存在不连续性,在观测范围内,全日内潮的动能及势能密度的最大值分别达到2kJ/m^2及3.5kJ/m^2,半日内潮的动能及势能密度的最大值分别达到1kJ/m^2及1.5kJ/m^2。  相似文献   

20.
Wave set-up in storm surges is studied using a numerical model for coasts in Tosa Bay, Japan, open to the Pacific Ocean. Simulation models employing only atmospheric pressures and winds as external forces are unable to properly simulate open coast storm surge heights, such as those due to Typhoon Anita (1970). However, the present study shows that a numerical model incorporating wave-induced radiation stresses, as well as wind stresses and pressure gradients, is able to account for the open coast surge heights. There is a maximum contribution of 40% by the radiation stresses to the peak sea level rises. This study also evaluates the effects of the tides; including the tides improves the agreement between the predicted water surface elevations and the observations. The difference in predictions between one-way coupling from wave to surge models and two-way coupling of the surge and wave models is found to be small.  相似文献   

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