Transformation of the Indonesian Throughflow Water by Vertical Mixing and Its Relation to Tidally Generated Internal Waves

Numerical experiments with two-dimensional nonhydrostatic model have been performed to investigate tidally generated internal waves at the Dewakang sill at the southern Makassar Strait where two large-amplitude “bumps” of relatively shallow water exist. We investigate the effect of these features on vertical mixing, with emphasis on the transformation of the Indonesian throughflow (ITF) water properties. The result shows that large-amplitude internal waves are generated at both bumps by the predominant M₂ tidal flow, even though the condition of the critical Froude number and the critical slope are not satisfied. The internal waves induce such vigorous vertical mixing in the sill region that the vertical diffusivity attains a maximum value of 6 × 10⁻³ m²s⁻¹ and the salinity maximum and minimum core layers characterizing the ITF thermocline water are considerably weakened. Close examination reveals that bottom-intensified currents produced mainly by the joint effect of barotropic M₂ flow and internal tides generated in the concave region surrounding both bumps can excite unsteady lee waves (Nakamura et al., 2000) on the inside slopes of the bumps, which tend to be trapped at the generation region and grow into large-amplitude waves. Such generation of unsteady lee waves does not occur in case of one bump alone. Trapping and amplification of the waves in the sill region induce large vertical displacements (∼60 m) of water parcels during one tidal period, leading to strong vertical mixing there. Since the K₁ tidal currents are relatively weak, large-amplitude internal waves causing intense vertical mixing are not generated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sub-surface temperature oscillations and associated flow in the western Bay of Bengal

Unusual temperature variations at subsurface depths were noticed while making continuous observations (for 13 h) on temperature, salinity and currents at a point in the vicinity of river Krishna in the western Bay of Bengal. Sharp temperature oscillations recorded at four different levels between 14 and 20·1 m had an average periodicity of about 1·6 h. Similar periodicities were also observed in the case of flow components. Computed Brunt-Vaisälä frequency, vertical shear and Richardson number showed remote possibilities of vertical mixing occurring in this area. These oscillations showed features of internal waves propagating with a speed of about 13·3 cm s⁻¹ and wavelengths between 0·8 and 1·3 km and apparently generated as a result of flood current passing over a submarine obstacle in the presence of stratification.     

分层海洋中运动物体生成的内波

该文提供分层海洋中运动物体生成内波的理论、数值和实验研究的背景资料的综述 ,并给出理论研究的 Green函数、正交模态模式和极点回避等方法的评述。数值研究给出数值求解Wronsky行列式的源求解方法及介绍直接差分计算含源内波方程和积分方程的方法。有关源致内波的实验研究 ,作者介绍物体在分层流水槽运动时生成内波的两个典型实验及其主要实验结果。最后评述船舶在海洋表面处生成表面波的研究方法 ,以此指导水下 Rankine卵形体生成内波的实验研究。     

Numerical and Physical Investigation on Vortex-Induced Vibrations of Marine Risers

1 .Introduction Risers ,in deep water and strong current environments ,are prone to vortex-induced vibrations(VIV) .Vortex-inducedforces may excite the risersintheir normal modes of transverse direction.Un-der the“lock-in”condition,large resonant oscill…     

海洋声层析研究的两个热点问题

综述了目前海洋声层析研究的两个热点问题 ,归纳了用声学方法监测气候变化和反演内波两个领域所取得的研究进展 ,总结了研究过程中存在的问题     

Numerical modeling on the interaction of internal solitary wave with slope-shelf and modal analysis

On the basis of a nonhydrostatic numerical model,the interaction of internal solitary wave with slope-shelf was studied.The breaking and polarity transformation were analyzed.A "kink" structure,due to shoaling topography and higher nonlinear effect,was found to be generated by the leading wave before breaking.Coherent vortex shedding behind the leading wave was presented.The evolution characteristics of the modal structure were analyzed based on the empirical orthogonal function method.The modal structure was complicated due to the effect of the variable topography,especially when breaking occurred.In the performed experiments,the contributions to the total variance from higher mode jumped from no more than 20% to over 40%.     

Infragravity waves with internal wave characteristics in the south of the Bohai Sea of China

The measurements by using ADCP (500 KH) and CTD were made during August 2000 in the south (37°55''N, 120°25''E) of the Bohai Sea, where the water depth was about 16.5m. The data of horizontal velocity with sampling interval of 2 min in 7 layers were obtained. The power spec-trum analysis of these data indicates that there are very energetic infragrvity waves with a period of about 6 min. The coherence spetrum analysis and the analysis of temporal variation of shear show that these infragravity waves are mainly the free wave model (properties of edge waves), in the meantimethey possess some characteristics of internal waves, which are likely due to the distinctive marine environment in this area. It is speculated on that the instability processes (chiefly shear instability) of sheared stratified tidal flow owing to the effect of sea-floor slope in the coastal area might be the main mechanism generating these infragravity waves.     

45以人为本 以研促教 依法治校——银川

职工209人,专业技0宁夏政报48G639.28H130;14;G;H;H130_14;46人才兴企 品牌强企 管理治企——银川市烟草专卖局(公司) 银川市烟草专卖局[公司],银川市烟草专卖局(公司)坚持以科学发展观为指导,牢固树立"国家利益至上、消费者利益至上"的行业共同价值观,紧跟行业形势,抓住     

库仑土压系数简易计算法

根据库仑主动土压力系数与填土内摩擦角、坡角、墙背倾角等参数的内在关系,对库仑主动土压力系数随不同参数的变化规律进行了分析,并在原数解法的基础上推导出一种新的简易计算公式。通过数解法与简易法的对比分析表明,当保证率为95%时,简易法相对于库仑计算值的最大误差小于14%。     

ŒDIPUS: a new tool to study the dynamics of planetary interiors

We present a new numerical method to describe the internal dynamics of planetary mantles through the coupling of a dynamic model with the prediction of geoid and surface topography. Our tool is based on the simulation of thermal convection with variable viscosity in a spherical shell with a finite-volume formulation. The grid mesh is based on the 'cubed sphere' technique that divides the shell into six identical blocks. An investigation of various numerical advection schemes is proposed: we opted for a high-resolution, flux-limiter method. Benchmarks of thermal convection are then presented on steady-state tetrahedral and cubic solutions and time-dependent cases with a good agreement with the few recent programs developed to solve this problem.
A dimensionless framework is proposed for the calculation of geoid and topography introducing two dimensionless numbers: such a formulation provides a good basis for the systematic study of the geoid and surface dynamic topography associated to the convection calculations. The evaluation of geoid and surface dynamic topography from the gridded data is performed in the spectral domain. The flow solver is then tested extensively against a precise spectral program, producing response functions for geoid as well as bottom and surface topographies. For a grid mesh of a reasonable size (6 × 64 × 64 × 64) a very good agreement (to within ∼1 per cent) is found up to spherical harmonic degree 15.