珠江磨刀门河口环流结构动力特征分析

河口环流结构关系到物质输运、泥沙沉积和地貌变化等物理过程。根据2019年磨刀门河口原型观测平台洪枯季连续观测分层潮流资料,统计洪枯季、大小潮河口东、西汊的涨落潮流及历时变化特征,利用理论方法解析河口东西汊平面环流和重力环流结构,进一步引入混合参数研究河口纵向环流中的潮汐应变环流。研究发现枯季东、西汊在转潮时刻存在东涨西落的平面环流结构,洪季平面环流特征较不明显;枯季重力环流强度整体略大于洪季,西汊重力环流强于东汊,表层向海环流流速可达0.2～0.25 m/s,而底层向陆环流流速相对较小。洪季大潮期由潮不对称性驱动的潮汐应变环流相对较大,进而增强了纵向环流的强度。河口垂向余流结构同样表现洪枯季、大小潮的变化规律。洪季余流整体较大,西汊在小潮期表层余流流速超过0.6 m/s,而东汊余流则明显呈现表层向海、底层向陆的分布特征,枯季余流整体较小,表明其对物质输运和河口地形塑造作用较弱。     

象山港内湾潮汐应变对横向流及其余环流垂向空间结构的调控研究

横向流 (垂直于海湾主轴方向的流动) 对横向动量以及物质分布具有重要影响。已往研究表明,潮汐应变对横向流的垂向空间结构具有重要的调控作用。但这种认识仅局限于强层化海区,弱层化条件下潮汐应变对于横向流空间结构的影响仍未可知。为此,本文以象山港为例,基于实测数据阐释了弱层化条件下潮汐应变对横向流及其余环流垂向空间结构的调控作用。结果显示,象山港内湾横向流的垂向空间结构随大小潮呈现出明显的变化规律。大潮时,潮汐应变现象明显,涨潮时较强的垂向混合使得横向流在高潮阶段呈现出一层结构;落潮时垂向混合较弱,横向流在低潮时呈现两层结构。小潮时,潮汐应变受到抑制,垂向混合在涨落潮时均较弱,因此横向流在高低潮阶段均呈现出两层结构。经过潮时均进一步得到的横向余环流呈现出上层向南、下层向北的两层结构。由于潮汐应变的大小潮变化,横向余环流的反转深度反转点自大潮到小潮呈现出上升的趋势。     

长江河口北槽弯道横向次生流、混合与层化

2013年2月25至26日(枯季/大潮)、7月23至24日(洪季/大潮)分别在长江河口北槽弯道沿着3条横向测线CS6、CSW和CS3(每条测线上有北、中、南3个站位)测得水位、流速、盐度和含沙量的时间序列资料。通过这些资料的定量计算、分析,理解弯道横向次生流、混合与层化的时、空变化和各种物理机制及其相对重要性。3条横向测线均存在横向次生流,且横向测线CS3还出现横向次生环流。枯、洪季,仅在横向测线CS6、CS3出现环状欧拉余流。枯、洪季,沿着横向测线CS3,3个站位的横向斜压梯度比离心加速度和科氏加速度都大1~2个数量级,而后两项大小接近且数量级都是10-4,罗斯贝数在1左右。这些表明:横向次生流受横向斜压梯度、离心加速度和科氏加速度共同驱动,前一项相对于后两项更加重要。沿着3条横向测线:1)枯、洪季大潮,平均势能差异分别约为54.23、66.56 J/m3,表明洪季层化强于枯季;2)枯季涨潮,平均的势能差异普遍小于落潮,而洪季涨潮,平均的势能差异普遍大于落潮,表明枯、洪季湍流混合均存在潮汐不对称性;3)枯季,由横向、纵向水深平均应变(ΦS-y、ΦS-x)引起的势能差异变化率的范围分别是-67×10~(-3)~37×10~(-3)、-7×10~(-3)~11×10~(-3)W/m~3,而洪季,相应的范围分别是-45×10~(-3)~30×10~(-3)、-14×10~(-3)~13×10~(-3)W/m~3,表明枯、洪季差异不明显,横向水深平均应变(ΦS-y)均大于纵向水深平均应变(ΦS-x),前项对水体混合与层化的影响更大;4)枯季大潮,纵向平流(ΦA-x)、横向平流(ΦA-y)、纵向水深平均应变(ΦS-x)和横向水深平均应变(ΦS-y)的潮汐平均绝对值占四项总和之比例分别为26%、33%、18%和23%,而洪季大潮,相应的值的比例分别为13%、9%、22%和56%,表明枯季,平流项(ΦA-y最大)对混合与层化的控制可能占主导地位;洪季,应变项(ΦS-y最大)可能占主导地位。无量纲数(m)被用于判别横向平流(ΦA-y)、横向水深-平均应变(ΦS-y)的相对重要性。一个概念性模式被用于显示层化与横向次生流/环流的相互关系。     

一个考虑潮汐、中尺度涡和地形影响的南海底部环流诊断模型

本文构造了一个考虑潮汐、中尺度涡和地形影响下的南海底部环流诊断模型。在该模型中,潮汐混合和涡致混合引起的垂直速率用一个类似的改进参数化方案来表示。该模型结果显示在南海深层吕宋海峡"深水瀑布"和斜压影响最大,潮汐作用和中尺度涡影响次之,风场的影响最小。斜压影响的整体效应与其他因素相反。潮汐混合与涡致混合具有明显的地形依赖性。潮汐混合主要集中在南海北部海盆地形较为陡峭的陆坡区和南海中部海山区,而涡致混合主要集中在海盆西边界区以及中部海山区。在不考虑吕宋海峡"深水瀑布"、潮汐和中尺度涡的情况下(对应吕宋海峡关闭),南海底部环流为反气旋式环流。考虑吕宋海峡"深水瀑布"后,南海底层环流为气旋式环流,而潮汐混合和涡致混合起到加强整个气旋式环流强度的作用。此外,该模型还给出了南海底部环流量级大小与地形坡度之间的密切关系,即地形坡度较大的地方,其流速也大。这对于现场观测有着一定的参考意义。最后,本文用尺度分析的方法从理论上分析了该模型的适用性,证实了该模型具有一定的可靠性。     

夏季长江河口层化与湍流混合特征分析

利用2016年夏季长江河口现场水文特性与湍流微结构观测资料, 分析了长江河口水体温盐结构、层化发育、湍流与混合特征。结果表明: 1)夏季长江河口水体密度层化结构明显, 根据各层水体密度梯度差异, 可将水体分为底部混合层和上层密度跃层, 两部分的密度层化界限与浮力频率等值线lg N ² = - 4.0接近。2)底部混合层湍动能耗散率大, 层化结构弱, 水体分层稳定性弱; 上层密度跃层湍动能耗散小, 层化结构强, 水体分层稳定性强, 这有利于河口内波的发育与传播。3)在密度层化的作用下, 水体的湍动能耗散率、湍动能剪切生成及浮力通量的能量关系在一定范围内符合湍动能局部能量平衡方程。不同层之间的湍流弗劳德数Fr_t和湍流雷诺数Re_t在Fr_t-Re_t平面上呈现明显的分区, 与经典的分层剪切流理论基本吻合。     

泉州湾水体结构的潮周期变化

泉州湾6个站点的观测数据显示：内湾涨潮流历时由底层向表层逐渐变短,而落潮流历时则逐渐变长;同时,各个站点实测的盐度水深结构也具有明显的潮周期变化特征,这可能与局地水体的层化和混合机制的交替变化密切相关．进一步定量分析S2站位上影响水体结构变化的四种机制发现：外湾的河口环流作用与潮汐张力、风混合以及潮汐混合作用相比要小一个量级．在一般天气条件下的大潮周期,潮汐混合与潮汐张力相互竞争是导致水体结构交替变化的根本原因;小潮周期由于潮流混合作用减弱,水体层化现象得以持续较长时间,风的搅动在特定时刻可以起到削弱层化结构的作用．     

中国物理海洋学研究70年:发展历程、学术成就概览

本文概略评述新中国成立70年来物理海洋学各分支研究领域的发展历程和若干学术成就。中国物理海洋学研究起步于海浪、潮汐、近海环流与水团,以及以风暴潮为主的海洋气象灾害的研究。随着国力的增强,研究领域不断拓展,涌现了大量具有广泛影响力的研究成果,其中包括:提出了被国际广泛采用的“普遍风浪谱”和“涌浪谱”,发展了第三代海浪数值模式;提出了“准调和分析方法”和“潮汐潮流永久预报”等潮汐潮流的分析和预报方法;发现并命名了“棉兰老潜流”,揭示了东海黑潮的多核结构及其多尺度变异机理等,系统描述了太平洋西边界流系;提出了印度尼西亚贯穿流的南海分支(或称南海贯穿流);不断完善了中国近海陆架环流系统,在南海环流、黑潮及其分支、台湾暖流、闽浙沿岸流、黄海冷水团环流、黄海暖流、渤海环流,以及陆架波方面均取得了深刻的认识;从大气桥和海洋桥两个方面对太平洋–印度洋–大西洋洋际相互作用进行了系统的总结;发展了浅海水团的研究方法,基本摸清了中国近海水团的分布和消长特征与机制,在大洋和极地水团分布及运动研究方面也做出了重要贡献;阐明了南海中尺度涡的宏观特征和生成机制,揭示了中尺度涡的三维结构,定量评估了其全球物质与能量输运能力;基本摸清了中国近海海洋锋的空间分布和季节变化特征,提出了地形、正压不稳定和斜压不稳定等锋面动力学机制;构建了“南海内波潜标观测网”,实现了对内波生成–演变–消亡全过程机理的系统认识;发展了湍流的剪切不稳定理论,提出了海流“边缘不稳定”的概念,开发了海洋湍流模式,提出了湍流混合参数化的新方法等;在海洋内部混合机制和能量来源方面取得了新的认识,并阐述了混合对海洋深层环流、营养物质输运等过程的影响;研发了全球浪–潮–流耦合模式,推出一系列海洋与气候模式;发展了可同化主要海洋观测数据的海洋数据同化系统和用于ENSO预报的耦合同化系统;建立了达到国际水准的非地转(水槽/水池)和地转(旋转平台)物理模 型实验平台;发展了ENSO预报的误差分析方法,建立了海洋和气候系统年代际变化的理论体系,揭示了中深层海洋对全球气候变化的响应;初步建成了中国近海海洋观测网;持续开展南北极调查研究;建立了台风、风暴潮、巨浪和海啸的业务化预报系统,为中国气象减灾提供保障;突破了国外的海洋技术封锁,研发了万米水深的深水水听器和海洋光学特性系列测量仪器;建立了溢油、危险化学品漂移扩散等预测模型,为伴随海洋资源开发所带来的风险事故的应急处理和预警预报提供科学支撑。文中引用的大量学术成果文献(每位第一作者优选不超过3篇)显示,经过70年的发展,中国物理海洋学研究培养了一支实力雄厚的科研队伍,这是最宝贵的成果。这支队伍必将成为中国物理海洋学研究攀登新高峰的主力军。     

调水调沙影响下黄河口泥沙异重流过程

利用黄河干流大型水库进行调水调沙,在短期内将大量沉积物快速输送入海,是河口泥沙异重流触发的重要窗口期。根据2010年调水调沙期间黄河口沉积动力现场观测资料,建立覆盖整个渤海海域的ROMS数学模型,以黄河利津站逐日水沙数据和海域潮汐、风场数据作为模型驱动条件,模拟调水调沙期间的河口泥沙异重流发育过程。模拟结果显示,在没有大风扰动的情况下,河流入海悬沙浓度29.0 kg/m~3时会在河口产生高密度泥沙异重流。黄河冲淡水携带大量悬浮物从河口流出后,与海水迅速混合,在潮流影响下,冲淡水舌随时间由西北向东南偏转,输运至莱州湾西侧。淡水和沉积物主要以表层羽状流和底层异重流形式输运:表层羽状流扩展范围较大,输运路径为河口西北方向-远岸(河口东北区域)-莱州湾西侧;底层异重流扩散范围较小,输运路径为河口西北方向-河口沿岸(东)-莱州湾西侧。河口泥沙异重流生消和水体垂向结构存在周期性变化特征:落潮时段异重流发育较好,水体层化增强;涨潮时段异重流逐渐消亡,水体混合增强。估算出黄河口清水沟清8叉流路主泓区内水体由河口径流、潮汐应变和潮汐搅动引起的势能变化率,其中潮汐应变和潮汐搅动起主导作用,比河口径流引起的势能变化率高出2～3个数量级(102～103)。     

椒江河口层化动力特性研究

基于椒江河口大、小潮期间水位、流速、盐度和悬沙浓度观测数据,研究了椒江河口主潮汐通道的水动力、盐度和悬沙浓度的时空变化特征,解释了高浊度强潮作用下的层化物理机制。椒江河口大潮期悬沙浓度和盐度均大于小潮期,主潮汐通道区域落潮期悬沙浓度大于涨潮期;盐度随潮变化,盐水锋面出现在S2测站,锋面附近出现最大浑浊带;自陆向海,悬沙浓度递减,盐度递增;随水深增加,悬沙浓度与盐度递增。Richardson数与混合参数显示,盐度和悬沙引起的层化现象,是随着潮汐的变化而变化,涨潮时的层化均强于落潮,小潮时的层化持续时间最长,区域更广。混合参数随潮周期变化,大潮期高于临界值1.0,小潮期低于临界值1.0。小潮期水体层化强于大潮期;潮汐应变项是影响势能差异变化率的重要因素;落潮期间层化向混合状态转化,涨潮相反。     

黄海温度锋及断面水温分布数值预报试验硏究

自Simpson和Hunter(1974)在对夏季爱尔兰海的研究中提出潮混合控制潮汐锋的概念以来,人们相继在许多强潮浅水区发现了潮汐锋现象,并做了大量的研究工作,对锋区的流场结构等特征,以及潮汐锋对周围环境的影响等有了更多的了解。在我国,赵保仁(1985)首先提出黄海存在潮汐锋现象,认为冷水团的温度锋可看作是底层的潮汐锋,并可利用近最大潮流流速计算层化参量来确定黄海潮汐锋(从而亦即温度锋)的位置,而且还可以根据已有调查资料和卫星图片揭示它的一些变化规律。他与合作者的一系列研究工作表明:黄海的潮混合及潮汐锋现象对黄海的温盐和水团分布、层化现象、强温跃层的分布变化、黄海的水平和垂直环流有重要影响和直接关系,进而可以推测黄海的潮混合及潮汐锋现象对黄海的物质输运、生态环境等有着重要的影响,因此研究黄海潮混合形成的温度锋和断面温度分布的数值预报方法是非常有必要的。 以往关于潮汐锋的数值研究大多数是诊断模式,用于求解潮汐锋形成以后锋区的环流结构等,而用数值方法模拟潮汐锋的形成和演化的工作却很少。在国外,只有王东平等(Wang et al.,1990)用二维模型,对垂直涡动扩散和粘性系数采用Munk-Anderson格式与湍流封闭格式嵌套的方法以反映边界层的作用,利用实测的大气强迫力和数值计算的潮流模拟了英国Celtic海的潮汐锋和海洋层化的变化问题,尚未涉及潮汐锋的形成过程。在国内,Bi和Zhao(1993)用一个二维数值模式对黄海34°N的潮汐锋进行了模拟,较好地模拟了从4月到8月潮汐锋的形成和演化过程。在此基础上,我们将进一步利用潮流分布及海面的热量和动量输入条件,以垂直均匀状态为初始条件,模拟黄海各主要断面的温度分布、温度锋和温跃层在增温期的形成和演化过程。     

Estuarine salt conservation: a Lagrangian approach

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.     

Turbulent mixing in a small estuary: Detailed measurements

Between 2003 and 2007, a series of field studies were performed in a typical small coastal plain type estuary (Eprapah Creek) located on the Southeast coast of Australia. The aim of these field studies was to investigate the turbulence and turbulent mixing properties in the estuarine zone. During these studies, high frequency turbulence and physio-chemistry data were collected continuously over a relatively long duration (up to 50 h). This article provides a summary of the key outcomes of these studies, highlighting the implications that these findings have on the modelling of small estuaries. The studies showed that the response of the turbulence and water quality properties were distinct under spring and neap tidal forcing and behaved differently in the middle and upper estuarine zones. The behaviour of turbulence properties to spring tidal forcing differed from that observed in larger estuaries and seemed unique to small estuarine systems. An investigation of several key turbulence parameters used in the modelling of estuarine mixing showed that many assumptions used in larger estuaries must be applied with caution or are simply untrue in small estuaries. For example the assumption that the mixing coefficient parameters are constant over the tidal cycle in a small estuary is simply untrue. These distinctions between the turbulence and mixing properties in small and large estuarine systems highlight the need for the continued study of small estuaries, so this type of system can be properly understood.     

The influence of wind on the water age in the tidal Rappahannock River

Wind plays an important role in regulating mixing/stratification, estuarine circulation, and transport timescale in estuaries. A three-dimensional model was used to investigate the effect of wind on transport time by using the concept of water age (WA) in the tidal Rappahannock River, a western tributary of the Chesapeake Bay, USA. The model was calibrated for water level, current, and salinity. A series of experiments regarding the effects of wind on WA was conducted under various dynamic conditions. The effect of wind on transport timescale depends strongly on the competition between the wind and buoyancy forcings, and on the pre-status of the circulation. A down-estuary wind generally decreases WA along the estuary. An up-estuary wind increases WA substantially because it changes the vertical mixing and estuarine circulation more significantly. When the buoyancy forcing increases, the up-estuary wind effect decreases whereas the down-estuary wind effect increases. A 2-day period wind pulse with a maximum speed of 15 m s⁻¹ can alter WA for 3 days; but the wind influence on WA lasts up to 40 days in the simulation. Both local and non-local wind forcings alter WA distribution. The local wind enhances vertical mixing and changes the gravitational circulation in the downstream portion of the estuary whereas it enhances transport in the freshwater portion of the estuary. Consequently, the local wind has a significant impact on WA distribution. In contrast, the non-local wind does not change the gravitational circulation significantly by imposing setup (setdown) of water level at the open boundary, resulting in a lesser impact on WA distribution.     

Similitude of the hydraulic model experiment for tidal mixing

The treatment of diffusion due to the tidal current in the near-shore ocean, and the similitude in the hydraulic model experiment are studied.In broad and shallow tidal bays and in the coastal seawaters near irregular boundaries, horizontal eddy-currents induced geometrically and turbulence caused by their cascading have predominant effect on dispersion of river and waste waters. These turbulent diffusion processes are similarly reproduced in the Froude models of turbulent resume, by adding the similitude for the self-similar structure of the spectral density of turbulence, or the eddy diffusivity. The similitude means to take the scale ratios of the time and the vertical length as the two-thirds power of the scale ratio of the horizontal length.Similitudes are also derived for the system of the gravitational circulation, the stratification and the salt-mass transport in partially and well-mixed estuaries. Generally, the vertical eddy diffusivity must be exaggerated by a half power of the model distortion externally by some methods of agitation. When the tidal bay is broad and very shallow, the Rayleigh number and the Hansen number are small, and the effect of density current and stratification on the flushing is small. Instead the effect of local eddies, geometrically induced tidal residual circulations become predominant. In this special case, there is no need to satisfy the similitude for density difference and vertical shear effects on dispersion.     

Tidal and river discharge forcing upon water and sediment circulation at a rock-bound estuary (Guadiana estuary,Portugal)

The relative impacts of tidal (neap, spring) and river discharge (including a flood event) forcing upon water and sediment circulation have been examined at the rock-bound Guadiana estuary. Near-bed and vertical profiles of current, salinity, turbidity, plus surface suspended sediment concentrations (SSC, at some stations only), were collected at the lower and central/upper estuary during tidal and fortnightly cycles. In addition, vertical salinity and turbidity profiles were collected around high and low water along the estuary. Tidal asymmetry produced faster currents on the ebb than on the flood, especially at the mouth. This pattern of seaward current dominance was enhanced with increasing river flow, due to horizontal advection that was confined within the narrow estuarine channel. The freshwater inputs and, at a degree less, the tidal range controlled the vertical mixing and stratification importance. Well-mixed (spring) and partially stratified (neap) conditions alternated during periods of low river flows, with significant intratidal variations induced by tidal straining (especially at the partially stratified estuary). Highly stratified conditions developed with increasing river discharge. Intratidal variability in the pycnocline depth and thickness resulted from current shear during the ebb. A salt wedge with tidal motion was observed at the lower estuary during the flood event. Depending on the intensity of turbulent mixing, the residual water circulation was dominantly controlled either by tidal asymmetry or gravitational circulation. The SSC was governed by cyclical local processes (resuspension, deposition, mixing, advection) driven by the neap-spring fluctuations in tidal current velocities. More, intratidal variability in stratification indicated the significance of tidal pumping at the partially and highly stratified estuary. The estuary turbidity maximum (ETM) was enhanced with increasing current velocities, and displaced downstream during periods of high river discharge. During the flood event, the ETM was expelled out of the estuary, and the SSC along the estuary was controlled by the sediment load from the drainage basin. Under these highly variable river flow conditions, our observations suggest that sand is exported to the nearshore over the long-term (>years).     

Estuarine Physical Processes Research: Some Recent Studies and Progress

The literature on estuarine physical studies is vast, diverse and contains many valuable case studies in addition to pure, process-based research. This essay is an attempt to summarize both some of the more recent studies that have been undertaken during the last several years, as well as some of the trends in research direction and progress that they represent. The topics covered include field and theoretical studies on hydrodynamics, turbulence, salt and fine sediment transport and morphology. The development and ease-of-application of numerical and analytical models and technical software has been essential for much of the progress, allowing the interpretation of large amounts of data and assisting with the understanding of complex processes. The development of instrumentation has similarly been essential for much of the progress with field studies. From a process viewpoint, much more attention is now being given to interpreting intratidal behaviour, including the effects of tidal straining and suspended fine sediment on water column stratification, stability and turbulence generation and dissipation. Remote sensing from satellites and aircraft, together with fast sampling towed instruments and high frequency radar now provide unique, frequently high resolution views of spatial variability, including currents, frontal and plume phenomena, and tidal and wave-generated turbidity. Observations of fine sediment characteristics (floc size, aggregation mechanisms, organic coatings and settling velocity) are providing better parameterizations for sediment transport models. These models have enhanced our understanding both of the estuarine turbidity maximum and its relationship to fronts and intratidal hydrodynamic and sedimentological variability, as well as that of simple morphological features such as intertidal mudflats. Although few, interdisciplinary studies to examine the relationships between biology and estuarine morphology show that bivalve activity and the surface diatom biofilm on an intertidal mudflat can be important in controlling the erosion of the surface mud layer.     

珠江河口盐度和输运过程对未来海平面上升的响应

研究海平面上升对河口的影响情况有助于了解输运过程的变化,基于21世纪海平面上升预测研究(陈长霖,2012;张吉,2014),本文选取珠江河口这一径优型与潮优型并存的河口为研究区域,利用数值模拟的方法,研究其在未来海平面上升后可能出现的响应。结果表明,河口的平均盐度、咸潮上溯距离和层化强度都将随着海平面的上升而增加,这些因素的变化有着明显的季节性。伶仃洋平均盐度在4月和10月增加更多;伶仃洋枯水期咸潮上溯距离的增量大于丰水期,磨刀门则相反;伶仃洋丰水期层化强度及其增量都要大于枯水期。海平面上升后的输运过程响应结果显示:(1) 垂向输运时间将增加,虽然海平面上升带来的潮差潮流的增强将加强垂向混合,但是层化的加强会削弱垂向交换。垂向输运时间的增加是由于层化的加强,层化加强抑制了潮汐变化带来的影响,表层水更难交换到底层; (2) 南北向河口环流将加强,表层余流向海加强,底层余流向陆加强,南北向余流整体向海减小。造成这些现象的主要原因是海平面上升后水深增加带来的河道比降的减小和压力梯度力的改变。     

瓯江河口盐度层化数值研究

瓯江口是一个径流量变化剧烈的强潮河口。本文基于非结构网格FVCOM模型,建立瓯江口海域大范围三维数学模型,研究不同时间尺度（潮周期、大-小潮）的盐度变化,并利用势能异常动力方程对数值模拟结果分析了瓯江口层化过程的动力机制。同时,利用河口R_i数和层化参数△s/<s>研究了不同时间尺度的层化稳定性及其空间变化,得出决定层化状态的潮差和径流量的阈值。结果显示：瓯江北口上段、中段和口门在潮差分别超过3.8m、4.0m和4.6m时呈完全混合状态。当径流量小于280 m³/s或大于510 m³/s,北口上段持续完全混合;而在口门附近,完全混合和层化的临界径流量约为280 m³/s。研究认为瓯江河口北口存在周期性的层化,北口下段在落潮和涨潮初期呈部分混合状态,而其它时段为完全混合。上段只在落潮初期存在层化。层化增强主要是纵向对流与横向速度剪切导致,而湍混合和纵向潮应力是层化减弱的主要因素。     

象山港盐度分布和水体混合 Ⅱ.混合分析

利用１９８１－１９９０年象山港的实测水文断面资料和盐度通量分析方法定量检验了各种动力因子对象山港水体混合的贡献,探讨了象山港水体混合的控制机理。象山港牛鼻水道至佛渡水道为平流和潮弥散混合区,水体纵向混合较好。象山港狭湾内段的潮混合强度较弱,垂向环流和潮振荡的垂向切变作用突出,水体纵向混合较狭湾外差。象山港湾外段为内段与田外的过渡区,各种混合因子的地位随季节和潮汛而变,水体混合状况介于狭湾内段和口外