利用理想模型实验研究涡旋碰撞海岛的过程

利用区域海洋模式(regional ocean modeling system,ROMS)构建理想模型实验来探讨f-平面上涡旋碰撞海岛的过程。结果表明,在理想模型设定条件下,当北半球的反气旋式涡旋以一定速度与尺度相当的海岛发生正面碰撞时,反气旋式涡旋的部分涡度会从涡旋移动方向的左侧"绕"过海岛形成一个新的反气旋式涡旋,同时,在碰撞过程中,会在移动方向碰撞点的右侧形成一个新的气旋式涡旋。在碰撞过程中,海岛主要起阻挡作用,产生碰撞方向水流速度的切变导致涡度梯度的增加,从而使涡旋结构中的正负涡度发生聚集,导致涡旋结构的改变。     

A statistical analysis of mesoscale eddies in the Bay of Bengal from 22–year altimetry data

本文使用一种基于SLA数据的涡旋识别方法,通过22年的AVISO高度计测高数据对孟加拉湾的中尺度涡特征进行了研究。本文主要分析了孟加拉湾涡旋的地理分布、涡旋极性、涡旋生命周期和传播距离、涡旋产生和消失位置、涡旋传播方向和移动轨迹、涡旋运动特征、涡旋属性的演化以及涡旋活动的季节和年际变化等特性。涡旋主要分布在孟加拉湾西部海域,并且大部分涡旋向西移动。涡旋极性分布显示气旋涡更经常出现在湾的西北部和南部,而反气旋涡主要出现在湾的东部。在22年间,共追踪探测到生命周期超过30天的气旋涡565个、反气旋涡389个;对所有生命周期和传播距离而言都是气旋涡数量居多。所有观测到的涡旋的运动属性分析显示气旋涡的涡旋平均振幅大于反气旋涡;对平均半径和平均移动速度而言,气旋涡和反气旋涡相差不大。而且,涡旋属性演化显示生命周期超过90天的涡旋具有明显的双阶段演化特征,包括一个前50天的涡旋成长阶段和一个50天之后的涡旋消亡阶段。针对涡旋活动的季节变化,气旋涡在春季居多而反气旋涡在夏季较多;长生命周期的涡旋季节分布显示在孟加拉湾涡旋活动具有明显的季节分布特征。涡旋数量的年际变化与EKE变化有一个明显的负相关。     

基于传输函数的中尺度涡旋时空连续可视化

本文结合二维流线可视化技术和中尺度涡旋识别技术,提出了3种中尺度涡旋时空连续可视化的方法:基于OW参数的涡旋可视化方法、基于栅格模板的涡旋可视化方法和基于矢量模板的涡旋可视化方法,这3种方法分别基于Okubo-Weiss算法、Faghmous的算法和Liu的算法来进行涡旋识别,同时将流场可视化的结果填充到涡旋内部,以获得更好的可视化效果。在可视化过程中本文引入了传输函数来对涡旋中的流线颜色和透明度进行实时交互,能够在控制界面上通过设置Key值点的颜色和位置来控制速度、涡度和OW参数等信息的显示效果。本文在性能和显示效果方面比较了3种方法的优劣。从性能上来讲,性能由高到低依次为:基于OW参数的涡旋可视化方法、基于栅格模板的涡旋可视化方法和基于矢量模板的涡旋可视化方法。从显示效果上来讲,基于OW参数的涡旋可视化方法在三者中最差,效果中有较多的杂乱的短线,同时涡旋边界较小,局限于涡旋核心区;基于栅格模板的涡旋可视化方法较第一种方法的显示效果有所提升,杂乱的短线较少,涡旋相对完整,但由于数据分辨率不够高的原因,在放大多倍后涡旋边界呈现锯齿状;基于矢量模板的涡旋可视化方法显示效果最好,涡旋完整、饱满。同时,因为首先进行了涡旋边界的重构,将涡旋边界矢量化,涡旋边界更加平滑。相对于传统长时间序列的涡旋可视化的方法而言,这3种方法提供了一个美观、动态和更富信息性的可视化方法,同时由于传输函数的加入,其可以成为科研人员研究涡旋的一个实用的工具。     

南极斯科舍海涡旋分布及其内部水文结构特征分析

南大洋涡旋在跨锋面物质热量输送方面具有重要作用,斯科舍海位于德雷克海峡东面,属于重要的经济渔区,因此针对斯科舍海的涡旋分布及其影响进行研究具有迫切意义.本文基于2005-2019年卫星遥感数据对斯科舍海涡旋进行了探测与追踪,并统计了涡旋半径、传播距离、生命周期等特征参数,分析涡旋的地理分布特点、涡旋跨锋面情况以及移动特...     

基于复杂网络的海洋涡旋移动特征研究——以南海为例

海洋涡旋作为一种快速连续变化的海洋现象,如何分析和挖掘其移动特征成为当前海洋涡旋定量研究的重点。本文引入空间数据挖掘的社区网络划分方法,将涡旋过程看作复杂的移动网络,对涡旋移动的聚集性特征进行探索和分析。首先,以网格为统计单元对1992-2011年近20年南海海洋涡旋移动数据进行组织,基于图论模型构建了涡旋瞬时移动（TP）,涡旋移动起止点（OD）,涡旋最小描述距离的特征点移动网（MDL）和涡旋过程移动再生数据（RSP）4种状态的海洋涡旋的移动网络图;其次,采用基于快速模块度优化的区域划分方法分别得到4种状态下涡旋移动的聚集性区域;最后,利用弦图对区域内和区域间涡旋移动规律进行了可视化分析,发现海洋涡旋的RSP数据能够弥补原始涡旋移动数据在区域划分方法中呈现的数量不足的问题,能够在足够数据量的情况下,有效地发现从起点到终点的主要移动通道和涡旋移动的聚集性区域,这些区域反映了南海涡旋从其产生、发展到结束整个演化过程的聚集性特征。     

北太平洋副热带逆流区中尺度涡旋的统计特征及其分布规律

本文基于卫星高度计得到的全球非线性中尺度涡旋数据集,分析了北太平洋副热带逆流(Subtropical Countercurrent.STCC)区域中尺度涡旋的统计特征,包括其基本特征、空间分布、传播特征、季节和年际变化;给出了该区域涡旋振幅、半径、旋转速度和罗斯贝数的分布直方图,并利用瑞利分布和对数正态分布对其进行了拟合。结果显示,涡旋振幅、半径、旋转速度和罗斯贝数的直方图很好地服从于对数正态分布。此外,通过与北太平洋中涡旋的对比研究,我们发现在STCC区中对数正态分布的拟合效果更好。本研究提高了对STCC区域中尺度涡旋统计特征的认识,明确了其与大洋中涡旋的区别;通过对数正态分布对涡旋特征的拟合,清晰地体现出了其分布规律,这在很大程度上降低了对观测数据的依赖,从而帮助我们更加有效地判断和预测涡旋特征的变化,同时为数值模式中涡旋的参数化提供了依据。     

东海黑潮周边中尺度涡的分布、运动规律以及生成机制

为了探究东海黑潮周边涡旋分布、形成机理及运动规律,基于法国国家空间研究中心(CNES)卫星海洋学存档数据中心(AVISO)的中尺度涡旋数据集展开了研究。首先,统计了近27年东海黑潮周边的涡旋分布,发现在黑潮弯曲海域产生了650个涡旋,在黑潮中段海域产生了271个涡旋,其中直径100~150 km之间的涡旋数量最多,涡旋振幅主要集中在2~6 cm。其次,分析了东海黑潮的运动路径和涡运动过程,结果表明,黑潮气旋式弯曲海域内侧易产生气旋涡,且移动路径较长,如台湾东北海域黑潮流轴气旋式弯曲处产生的涡旋,其平均位移达到了87.6 km;当反气旋式弯曲海域内侧产生反气旋涡时,涡旋往往做徘徊运动。黑潮中段海域的涡旋呈现出气旋涡在黑潮主轴西侧、反气旋涡在黑潮主轴东侧的极性对称分布特征,两类涡都沿黑潮主轴向东北方向移动。最后,结合再分析的流场、海面高度数据,讨论了涡旋运动规律和生成机制。黑潮弯曲处涡旋的生成与黑潮流体边界层分离有关,奄美大岛南部到冲绳岛西侧的黑潮逆流对黑潮中段海域涡的极性对称分布起到了关键作用,涡旋在运动过程中通常经历生长、成熟和衰变三个阶段。     

利用旋转平台模拟双河口羽流相互作用的研究

本文通过旋转平台实验室实验的方法,探讨了双河口情况下两个羽流将如何发生相互作用。在研究中,提出了一种新颖的技术对河口羽流的各切面流场进行测量,来获得河口羽流多个平面的速度场及涡度场,并基于此模拟了双河口羽流系统的准三维结构。通过对不同入流速度下的双河口羽流流场演变过程和内部结构进行了一系列对比研究,以期揭示上游河流的入流如何影响下游河口涡旋的形成及在羽流相互作用情形下各个羽流的演变。实验结果表明:随着上游入流流量的增加,上游羽流形成的沿岸流对下游河口涡旋沿岸迁移的促进和离岸输运的抑制作用将更加显著。特别是在上游入流流量等于或大于下游入流流量的情况下,下游羽流河口涡旋的体积增长明显较单一河口情况放缓。在上游入流流量较大的情况下,下游原有河口涡旋被推向更下游位置,在远离河口的位置形成另一个河口涡旋。在垂直方向上,我们可以观察到高上游入流流量条件下的下游河口涡旋的深度较小,更有利于形成三层流体的情况。本研究对多河口近海流域的营养盐及污染物的输运情况等社会和生态问题的研究有着重要的意义。     

南海中尺度涡的形转、内转及平移运动研究

中尺度涡旋的运动整体可分为两部分：平移及转动。平移指涡旋在整个生命周期内的水平移动,而转动除了包括内转 （海表地转流引起的涡旋自身水体转动） 外,还包括形转 （涡旋实际边界最佳拟合椭圆的转动）。本文基于 1993—2018 年共计 26 年间的卫星高度计涡旋识别与追踪数据,首次对南海中尺度涡旋的完整运动形式,即形转、内转、平移展开了系统的研究。其中,对内转及平移的分析,可通过涡旋的识别追踪数据集直接进行;为研究涡旋形转,提出了一种基于涡旋识别追踪数据自动提取涡旋形转信息的算法,以此得到涡旋形转方向、每天形转的角度以及形转圈数等信息,获得涡旋形转数据集。通过对涡旋识别追踪数据以及形转数据集的统计分析发现：南海涡旋的平移方向多为西向,且其速率呈偏态分布,主要以南海南部偏高。同样,涡旋的内转速率也呈偏态分布,高速率内转的涡旋主要分布在吕宋海峡附近。涡旋的形转主要以南海南部速率偏高,且与涡旋的寿命及长轴有一定的关系,倾向于随着涡旋寿命的增长、涡旋长轴的增大而变慢。同时南海涡旋的这三种不同运动形式之间也存在一定的相关性。     

基于客观方法的海洋三维涡旋核心线提取

涡旋核心线是海洋中尺度涡旋结构的重要组成要素,涡旋核心线提取和可视化对于切入中尺度涡三维结构研究、开展海洋物质能量垂直运输分析具有重要意义。本文基于客观参考框架和准则,提出了使用客观化的流场参数得到区域,并提取其山谷线作为涡旋核心线的方法,实现了对海洋三维结构中尺度涡旋核心线的提取和可视化。首先,引入了最优局部参考系,使速度、速度梯度等测度转换为在运动的参考系下保持不变的客观量,提升了在海洋科学实践中的可靠性和实用性。其次,针对含有垂向速度的海洋三维流场数据,计算其空间雅可比矩阵,展示了涡旋核心区域的三维结构,实现了海洋涡旋研究从二维到三维的提升。最后,分别在多个半径大小播撒流线种子点,分析不同旋转方向的涡旋,对已提取的涡旋核心线实验结果进行验证,证明了客观海洋三维涡旋核心线提取方法的有效性及可行性。     

Large-scale turbulence under a solitary wave: Part 2: Forms and evolution of coherent structures

The instantaneous turbulent velocity field produced by a broken solitary wave propagating on a 1 in 50 plane slope was measured in the longitudinal transverse plane in the middle part of the water column and near the bottom using a stereoscopic particle image velocimetry system. These measurements showed that large-scale turbulence first arrived in the form of a downburst of turbulent fluid. In the middle of the water column, the downbursts arrived shortly after the wave crest had passed. Each downburst was accompanied by two counter-rotating vortices. The latter grew rapidly in size to become a prominent feature of the flow field. Each vortex had a typical length scale of 1/2 to 1 water depth, and carried most of the turbulent kinetic energy in the region between the vortices. Near the bottom, the counter-rotating vortices were not as well defined and covered only a small plane area compared to the entire flow structure. The turbulent fluid descending from above diverged at the bed and the resulting flow structure developed an elongated shape as the source of down-flow travelled onshore with the broken wave. It was found that the transverse spacing between adjacent downbursts ranged from 2 to 5 times the local still water depth. Since vortices cannot end in the interior of the fluid, the counter-rotating vortices must extend to the free surface in the form of a vortex loop. It was suggested that these vortex loops were produced by bending and stretching of primary vorticity generated in the wave breaking process, possibly as a result of three-dimensional water surface deformation. The vortex loops were then carried downward by the falling water from the broken wave.     

三维顶板斜向驱动方腔流有限元并行计算

基于PETSc FEM开源代码,采用分步有限元算法和区域分解法,并行计算了不同雷诺数下的三维顶板斜向驱动方腔流问题。计算结果表明,当顶板沿其对角线方向运动时,流体与下游侧壁发生斜向碰撞后在下游对角处汇聚并形成射流,该射流在与底面、上游侧壁碰撞后形成较为复杂的涡流结构。雷诺数大小对三维顶板斜向驱动方腔流的涡流场结构形态具有重要影响。并行性能分析表明区域分解法能有效地提高三维粘性方腔流的计算速度。     

On the Dynamics of Inertial Particles in an Intensive Atmospheric Vortex

Izvestiya, Atmospheric and Oceanic Physics - The movement of inertial particles in intense vortices with a vertical axis in a gravity field is analyzed analytically. In this problem, the nonlinear...     

Eddy activity in the lee of the Hawaiian Islands

Persistent northeasterly trade winds have a substantial impact on the oceanic circulation around the Hawaiian Islands. A regional ocean model is applied to understand the effect of different temporal and spatial resolutions of surface momentum forcing on the formation of strong mesoscale vortices and on the simulation of realistic levels of eddy kinetic energy. The higher spatial and temporal resolutions of wind forcing is shown to substantially affect the vorticity and deformation field in the immediate lee of the Hawaiian Islands and produce patterns of eddy kinetic energy similar to observations. This suggests that the surface eddy field in the region is mostly dominated by the local surface momentum forcing. Mesoscale cyclones and anticyclones formed in the lee of the Island of Hawaii are shown to have different propagation patterns. Mesoscale cyclones are more confined to the lee and are hence subject to interactions with the strong wind forcing and deformation field as well as smaller vortices formed in the wake of the other islands. Mesoscale anticyclones show not only a tendency to propagate further westward, but also to persist as coherent features as they propagate, even at relatively lower values of relative vorticity. The large strain rates that affect the propagation of the cyclones cause them to break down into filaments of positive vorticity. Rossby numbers of O(1) within vortices and filaments indicate that nonlinear interactions between the wind stress and the vertical component of the relative vorticity field is potentially important in producing large vertical velocities. Modeled cyclonic eddies show a good resemblance to observations both in terms of vertical structure and propagation patterns.     

Scarifying and fingering surfaces of plunging jets

The local surface deformation resulting from the oblique impact of a columnar water jet has been computed, using a three-dimensional large eddy simulation, as a model of the overturning jet of a breaking wave. The emergence of the secondary jet from the front face of the initial jet has been examined and the organisation of the vortices within the jet characterised. As the secondary jet emerges, the vorticity field becomes unstable under the action of the strong shear beneath the jet surface and pairs of longitudinal counter-rotating vortices stretched along the direction of the jet projection are formed. The presence of these longitudinal vortex pairs creates convergent surface flows, resulting in the formation of longitudinal scars on the rear face of the projecting jet. Following significant growth of the scars on both its upper and lower surfaces, the jet decouples into fingers. The lateral widths of the longitudinal vortices provide a minimum measure of the finger size. A horizontal Froude number Fr_h, representing a measure of strength of horizontal shear in a gravity-dominated impacting flow is defined, which characterises the organisation of the longitudinal vortices occurring in the shear flow, and the resultant formation of scars and fingers. For higher Fr_h, stronger longitudinal vortices and deeper scars are formed at longer lateral intervals, enhancing the fingering process during the splashing event. Fundamental features of material transport in the vicinity of the surface of jets (e.g. gas transfer across a sea surface) are related to the entrainment of surface fluid by the longitudinal vortices, and is thus also characterised by Fr_h.     

Scour and Burial Mechanics of Objects in the Nearshore

A process-based, numerical, hydrodynamic vortex lattice mine scour/burial model (VORTEX) is presented that simulates scour and burial of objects of arbitrary shape resting on a granular bed in the nearshore. There are two domains in the model formulation: a far-field where burial and exposure occur due to changes in the elevation of the seabed and a near-field involving scour and transport of sediment by the vortices shed from the object. The far-field burial mechanisms are based on changes in the equilibrium bottom profiles in response to seasonal changes in wave climate and accretion/erosion waves spawned by fluxes of sediment into the littoral cell. The near-field domain consists of one grid cell extracted from the far-field that is subdivided into a rectangular lattice of panels having sufficient resolution to define the shape of the object. The vortex field induced by the object is constructed from an assemblage of horseshoe vortices excited by local pressure gradients and shear over the lattice panels. The horseshoe vortices of each lattice panel release a pair of vortex filaments into the neighboring flow. The induced velocity of these trailing vortex filaments causes scour of the neighboring seabed and induces hydrodynamic forces on the object. Scour around the object and its subsequent movement into the scour depression contribute to burial, while far-field changes in local sand level may increase burial depth or expose the object. Scour and burial predictions of mines and mine-like objects were tested in field experiments conducted in the nearshore waters off the Pacific coast of California at Scripps Pier, the Gulf Coast of Florida at Indian Rocks, and off the Atlantic coast of Massachusetts at Martha's Vineyard. Model predictions of mine scour and burial are in reasonable agreement with field measurements and underwater photographs.     

海洋中长生命反气旋涡在地形上的演变以及涡旋的合并现象

通过对海洋中长生命反气旋涡在Ｇａｕｓｓ型孤立地形上演变的研究,发现地形对长生命反气旋涡的发展和传播有相当重要的影响。在无地形作用的情况下,仅有反气旋涡能够存在于向西的均匀基流中,这个涡是长生命的,并且在西移过程中有明显的向西倾斜。然而当其上游存在一个孤立地形时,可以发现这个涡有一个向东的倾斜,它的强度将增强且向西的移速会增加,其规迹象陀螺的运动。另一方面,当两个强度相同的反气旋涡同时存在时,这两个     

三种叠放形式的圆管型人工鱼礁流场效应数值模拟与PIV试验研究

人工鱼礁单体按不同的数量和排列方式组合投放会产生不同的流场效应。圆管型礁为目前黄渤海区增殖礁的重要礁体型式,为优化该礁体的投放数量与排列方式,选择了3种不同叠放个数(1个、3个和6个)的圆管礁,设定了5个流速梯度(4.5、9.0、13.5、18.0和22.5cm/s),利用PIV粒子图像测速技术和Fluent数值模拟软件对圆管型人工鱼礁的流场进行水槽模型试验和数值模拟。结果表明,数值模拟结果与水槽试验结果基本吻合,误差在20%以下,表明数值模拟能够反映人工鱼礁的流场效应;当礁体叠放个数一定时,最大上升流流速、上升流高度和上升流面积均随来流速度的增加而增大,背涡流面积呈现不规则的变化;当来流速度一定时,最大上升流流速、上升流面积、上升流高度和背涡流面积均随礁体叠放个数的增加而增大。     

LIC color texture enhancement algorithm for ocean vector field data based on HSV color mapping and cumulative distribution function

Texture-based visualization method is a common method in the visualization of vector field data. Aiming at adding color mapping to the texture of ocean vector field and solving the ambiguity of vector direction in texture image, a new color texture enhancement algorithm based on the Line Integral Convolution (LIC) for the vector field data is proposed, which combines the HSV color mapping and cumulative distribution function calculation of vector field data. This algorithm can be summarized as follows: firstly, the vector field data is convoluted twice by line integration to get the gray texture image. Secondly, the method of mapping vector data to each component of the HSV color space is established. And then, the vector field data is mapped into HSV color space and converted from HSV to RGB values to get the color image. Thirdly, the cumulative distribution function of the RGB color components of the gray texture image and the color image is constructed to enhance the gray texture and RGB color values. Finally, both the gray texture image and the color image are fused to get the color texture. The experimental results show that the proposed LIC color texture enhancement algorithm is capable of generating a better display of vector field data. Furthermore, the ambiguity of vector direction in the texture images is solved and the direction information of the vector field is expressed more accurately.     

Interaction of an ensemble of vortices in the β-plane

The evolution of an ensemble of intense vortices in the β-plane is numerically simulated. In the process of evolution, vortices interact either directly or by means of the Rossby waves emitted by them. We show that the mean displacements of vortices of the ensemble along the meridian and, as a result, their energy losses are lower than for the isolated vortices evolving in the β-plane. This means that they are more stable than the isolated vortices. In addition, for vortices in the ensemble, the theoretical dependence of the energy of a vortex on its displacement from the initial latitude obtained for the motion of an intense isolated vortex in the β-plane is in good agreement with the experimental data. Translated by Peter V. Malyshev and Dmitry V. Malyshev