A spectral barotropic model of the wind-driven world ocean

A global spectral barotropic ocean model is introduced to describe the depth-averaged flow. The equations are based on vorticity and divergence (instead of horizontal momentum); continents exert a nearly infinite drag on the fluid. The coding follows that of spectral atmospheric general circulation models using triangular truncation and implicit time integration to provide a first step for seamless coupling to spectral atmospheric global circulation models and an efficient method for filtering of ocean wave dynamics. Five experiments demonstrate the model performance: (i) Bounded by an idealized basin geometry and driven by a zonally uniform wind stress, the ocean circulation shows close similarity with Munk’s analytical solution. (ii) With a real land–sea mask the model is capable of reproducing the spin-up, location and magnitudes of depth-averaged barotropic ocean currents. (iii) The ocean wave-dynamics of equatorial waves, excited by a height perturbation at the equator, shows wave dispersion and reflection at eastern and western coastal boundaries. (iv) The model reproduces propagation times of observed surface gravity waves in the Pacific with real bathymetry. (v) Advection of tracers can be simulated reasonably by the spectral method or a semi-Langrangian transport scheme. This spectral barotropic model may serve as a first step towards an intermediate complexity spectral atmosphere–ocean model for studying atmosphere–ocean interactions in idealized setups and long term climate variability beyond millennia.     

Numerical simulation of the upper ocean currents in South China Sea

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用广义随底坐标海洋模式研究南海2000年夏季环流

基于2000年8月在南海调查航次得到的水文资料,首次采用广义随底坐标形式的改进POM模式对南海夏季环流进行了数值研究.用正交曲线性水平网格覆盖观测区域,在垂向上对近表海面层次采用近似z坐标,而近底层则为随底坐标.在计算海区实际地形及假设的水平均匀而垂直层化的密度分布下,实施的两个数值计算试验表明,本模式采用的垂直坐标方案比传统的σ坐标方案优越,随底坐标模式因压力梯度项在起伏地形下产生的系统计算误差将变得十分的微小.在南海2000年夏季环流的实际计算中,首先对观测资料进行了60d的诊断计算,然后在诊断已得到的动力场结果基础上,又进行了10d左右的预报运行得到半诊断结果.从计算结果来看,它依赖于参数C_vis与C_dif的选择,特别是参数C_vis,文中取值为C_vis=C_dif=008.比较诊断与半诊断两个计算过程的结果,它们在定性上较为一致,在定量上有些差别.这是因为半诊断计算的方法对密度场作适当的动力调整,使其与地形、风场等更加匹配.在大尺度环流结构不受影响的情况下,尽可能地消除了小尺度噪声,可使计算得到的流场更为清晰.2000年8月南海计算区域环流的最大特点是多涡结构,其中有些反气旋暖涡和气旋式冷涡相间分布.在越南东南海域自表层至1000m水层稳定存在着一个显著的反气旋暖涡,其中心位置在11°51'N,112°07'E(诊断计算),水平尺度约为300km.此暖涡以东存在一个气旋式冷涡,这两个冷、暖涡是研究海区夏季环流的重要环流特征之一.在计算区域东北部夏季环流以反气旋环流系统为主;在计算区域东南部夏季环流以气旋系统为主;南海夏季环流分布,明显出现西部强化特征.     

渤海、黄海、东海冬季环流的数值模拟

在POM的基础上,建立一个σ坐标系下三维斜压预报模式,利用经过资料同化处理的周平均卫星遥感海面温度资料,考虑海底地形、外海出入流、海面风应力等因素的影响,较好的模拟了冬季渤、黄、东海环流的情况。     

Study on short-range numerical forecasting of ocean current in the East China Sea——Ⅰ Basic problems of ocean current forecasting and structure of the models

Ocean current forecasting is still in explorative stage of study. In the study, we face some problems that have not been met before. The solving of these problems has become fundamental premise for realizing the ocean current forecasting. In the present paper are discussed in depth the physical essence for such basic problems as the predictability of ocean current, the predictable currents, the dynamical basis for studying respectively the tidal current and circulation, the necessity of boundary model, the models on regions with different scales and their link. The foundations and plans to solve the problems are demonstrated. Finally a set of operational numerical forecasting system for ocean current is proposed.     

基于FVCOM 的渤海潮波数值模拟

基于有限体积法海洋数值模型(FVCOM),对渤海当前水深岸线状况下的潮汐潮流进行了数值计算。模式采用不规则三角形网格,较好地提高了黄河口处网格分辨率,模拟了渤海海域K1,O1,M2和S2四个主要分潮。利用渤海沿岸19个验潮站的资料对模拟结果进行了验证,K1分潮振幅绝均差2.39 cm,迟角绝均差4.36°,O1分潮振幅绝均差1.40 cm,迟角绝均差4.29°,M2分潮振幅绝均差为3.55 cm,迟角绝均差为5.69°,S2分潮振幅绝均差1.72 cm,迟角绝均差8.86°,结果显示各分潮模拟结果合理,较真实地反映了渤海海域四个分潮传播情况。     

Diurnal cycling of carbon monoxide (CO) in the upper ocean near Bermuda

A coupled photochemical–physical model for the upper ocean carbon monoxide concentration is presented. The coupled model uses a spectral optical model and a number of different mixing parameterizations. It is run using the meteorological forcing conditions measured during a 9-day investigation near Bermuda in the Sargasso Sea in March 1993 in the declining phase of the spring bloom. The baseline runs of the model are successful in simulating measurements made during the campaign, and form the basis of an optimization routine to find better estimates of the production and destruction constants of the photochemical tracer. The optimized values derived in this inverse procedure depend on the mixing parameterization and the assumed dark production rate of carbon monoxide.     

在大洋环流模型中对应于惯性内波破碎的垂直混合的一个参数化方案

Based on the theoretical spectral model of inertial internal wave breaking(fine structure) proposed previously, in which the effects of the horizontal Coriolis frequency component f-tilde on a potential isopycnal are taken into account, a parameterization scheme of vertical mixing in the stably stratified interior below the surface mixed layer in the ocean general circulation model(OGCM) is put forward preliminarily in this paper. Besides turbulence, the impact of sub-mesoscale oceanic processes(including inertial internal wave breaking product) on oceanic interior mixing is emphasized. We suggest that adding the inertial internal wave breaking mixing scheme(F-scheme for short) put forward in this paper to the turbulence mixing scheme of Canuto et al.( T-scheme for short) in the OGCM, except the region from 15°S to 15°N. The numerical results of F-scheme by using WOA09 data and an OGCM(LICOM, LASG/IAP climate system ocean model) over the global ocean are given. A notable improvement in the simulation of salinity and temperature over the global ocean is attained by using T-scheme adding F-scheme, especially in the mid- and high-latitude regions in the simulation of the intermediate water and deep water. We conjecture that the inertial internal wave breaking mixing and inertial forcing of wind might be one of important mechanisms maintaining the ventilation process. The modeling strength of the Atlantic meridional overturning circulation(AMOC) by using T-scheme adding F-scheme may be more reasonable than that by using T-scheme alone, though the physical processes need to be further studied, and the overflow parameterization needs to be incorporated. A shortcoming in F-scheme is that in this paper the error of simulated salinity and temperature by using T-scheme adding F-scheme is larger than that by using T-scheme alone in the subsurface layer.     

A new hybrid vertical coordinate ocean model and its application in the simulation of the Changjiang diluted water

Based on the analysis of the advantages and disadvantages of some vertical coordinates applied in the calculation of the Changjiang diluted water(CDW),a new hybrid vertical coordinate is designed,which uses σ coordinate for current and σ-z coordinate for salinity.To combine the current and salinity,the Eulerian-Lagrangian method is used for the salinity calculation,and the baroclinic pressure gradient(BPG) is calculated on the salinity sited layers.The new hybrid vertical coordinate is introduced to the widely used model of POM(Princeton Ocean Model) to make a new model of POM-σ-z.The BPG calculations of an ideal case show that POM-σ-z model brings smaller error than POM model does.The simulations of CDW also show that POM-σ-z model is better than POM model on simulating the salinity and its front.     

A Study of the Performances of Different Turbulence Schemes in Numerical Simulation of Hydrodynamics of a Semi-Closed Sea (Persian Gulf)

Complex process of turbulent mixing in Persian Gulf that is a semi-closed sea makes it a good media to test the performance of different turbulence schemes. In this research, we used the 3D ocean model COHERENS (COupled Hydrodynamical Ecological model for REgioNal Shelf seas) for the Persian Gulf with the open boundary in the Hormuz Strait. Of the turbulence schemes for the vertical diffusion available in the COHERENS, we tested four models to investigate the hydrodynamic characteristics of the Persian Gulf. The results show that all of the schemes presented the sea surface salinity (SSS) distribution rather accurately but the k-l and flow-dependent models results have better agreements with observations. The most noticeable difference between the results of four schemes is the differences found in the simulation of turbulent parameters. The turbulent closure schemes generally provide better results, but the algebraic schemes show turbulent parameters far from reality and they do not show substantial changes with time. Generally, the vertical structures of turbulence in the water basins and parameterization of turbulence in water column is very sensitive to the selection of the type of the turbulence scheme. However, large-scale structures that take place within the inflow and outflow area are approximately quasi-horizontal, and the vertical small-scale turbulence does not affect them as much. As a result, they show less sensitivity to the performance of various turbulence schemes.     

北部湾的环流和水团对季节性强迫的响应

In the past 20 a, the gulf-scale circulation in the Beibu Gulf has been commonly accepted to be driven by a wind stress or density gradient. However, using three sensitive experiments based on a three-dimensional baroclinic model that was verified by observations, the formation mechanisms were revealed： the circula- tion in the northern Beibu Gulf was triggered by the monsoon wind throughout a year; whereas the southern gulf circulation was driven by the monsoon wind and South China Sea （SCS） circulation in winter and sum- mer, respectively. The force of heat flux and tidal harmonics had a strong effect on the circulation strength and range, as well as the local circulation structures, but these factors did not influence the major circulation structure in the Beibu Gulf. On the other hand, the Beibu Gulf Cold Water Mass （BGCWM） would disappear without the force of heat flux because the seasonal thermocline layer was generated by the input of heat so that the vertical mixing between the upper hot water and lower cold water was blocked. In addition, the wind-induced cyclonic gyre in the northern gulf was favorable to the existence of the BGCWM. However, the coverage area of the BGCWM was increased slightly without the force of the tidal harmonics. When the model was driven by the monthly averaged surface forcing, the circulation structure was changed to some extent, and the coverage area of the BGCWM almost extended outwards 100%, implying the circulation and water mass in the Beibu Gulf had strong responses to the temporal resolution of the surface forces.     

蓬莱19-3 油田事故溢油数值模拟

利用FVCOM(Finite-volume coastal ocean numerical model)数值模型和MM5风场预报模式,在对渤海海域水动力场进行数值模拟的基础上,基于"油粒子"的欧拉-拉格朗日跟踪法和随机走动原理,并考虑风对溢油油膜漂移扩散的直接作用,建立了海洋溢油油膜漂移轨迹和扩散的数值预测模型。利用建立的模型对2011年6月蓬莱19-3油田事故溢油进行了数值模拟,模拟结果与RADARSAT卫星遥感监测数据相吻合。研究结果表明:在渤海中部地区夏季事故溢油模拟预测中,风漂移因子取0.024最为合理,模型可用于渤海蓬莱19-3油田附近事故溢油轨迹和扩散的快速预报,从而为该区域的溢油事故应急响应提供科学依据。     

台风影响下渤海及邻域海面风场演变过程的MM5模拟分析

在装有 L inux操作系统的 PC机上运行美国大气研究中心 ( NCAR)的非静力中尺度大气模式 MM5。运用 MM5的嵌套功能 ,以 30 km水平分辨率对台风 KAI- TAK( 2 0 0 0年第 4号 )影响渤海海区的时段进行数值模拟 ,同时给出了水平分辨率为 10 km的嵌套区内逐时的渤海海面风场。通过对台风中心位置、中心气压、风速分布与雨区分布等要素的模拟结果与实况的比较 ,证实该实验对台风过程的模拟较为成功。嵌套区内渤海海面风场也明显体现出了地形影响的特征。并尝试以T10 6格点资料的三维客观分析场结合高空及地面观测为模式提供初值场 ,6h/次预报场为模式提供时变边界条件 ,对渤海海面风场进行了 2 4 h时预报     

墨西哥湾海洋环境对蓝蟹(Callinectes sapidus)幼体分布和扩散的影响

本文以蓝蟹为例,研究海洋环境对甲壳动物幼体迁移规律和机制的影响。利用不规则三角形网格和有限体积模型(finite-volume coastal ocean model, FVCOM)耦合kinesis模型的方法,分析研究了墨西哥湾物理环境对蓝蟹(Callinectessapidus)幼体的分布和扩散途径的影响。蓝蟹在每年的四、五月份海水落潮期间产卵,通过跟踪算法从产卵区域沿着墨西哥湾海域进行模拟,获得了80天内蓝蟹幼体的粒子移动轨迹,记录并分析了幼体经过海域的盐度值。研究结果证明了该方法可有效模拟蓝蟹幼体在特定海域的迁移规律和扩散机制,进一步研究可为了解海洋物理环境对蓝蟹和其他渔业资源的影响提供借鉴。     

黄、东海环流的数值研究Ⅲ——正压环流的数值模拟

依据黄、东海环流的的动力学模型 ,运用“流速分解法”对黄、东海正压环流进行了数值模拟。计算结果表明冬季黄海正压环流主要受风应力影响 ,基本形态为黄海暖流由济州岛西南进入南黄海中部 ,其东西两侧分别为两支向南流动的沿岸流 ;夏季主要受到潮致体力的影响 ,为一逆时针涡旋。东海环流主要是边界力作用驱动的结果 ,东海黑潮、台湾暖流和对马暖流较稳定。冬季风应力对东海环流表层流场有消弱作用 ,在夏季则有一定增强作用。     

Research on the Effects of in-Line Oscillatory Flow on the Vortex-Induced Motions of A Deep Draft Semi-Submersible in Currents

A Deep Draft Semi-submersible (DDS) under certain flow conditions could be subjected to Vortex-Induced Motions (VIM), which significantly influences the loads on and life fatigue of the moorings and the risers. To investigate the VIM of a DDS with four rectangular section columns in waves coupled with a uniform current, a numerical study using the computational fluid dynamics (CFD) method was conducted. The issues of the VIM of multi-column floaters can be conveniently converted to the issues of oscillating cylinders in fluid cross flows. This paper looks into the CFD numerical simulation of infinite cylinders having rectangular sections in a two-dimensional sinusoidal time-dependent flow field coupled with a uniform current. The resulted hydrodynamic forces and motion responses in different oscillatory flows plus currents both aligned in the same direction for the incidence of 135° of the DDS relative to the flow are compared with the ones in current only cases. The results show that the VIM response of this geometric arrangement of a DDS with four rectangular columns in a current combined with oscillatory flows is more evident than that in the current only case. The oscillatory flows and waves have the significant influence on the VIM response, forces and trajectory, in-plane motions of the DDS.