Eddies and Tropical Instability Waves in the eastern tropical Pacific: A review

Mesoscale eddies and tropical instability waves in the eastern tropical Pacific, first revealed by satellite infrared imagery, play an important role in the dynamics and biology of the region, and in the transfer of mass, energy, heat, and biological constituents from the shelf to the deep ocean and across the equatorial currents.From boreal late autumn to early spring, four to 18 cyclonic or anticyclonic eddies are formed off the coastal region between southern Mexico and Panama. The anticyclonic gyres, which tend to be larger and last longer than the cyclonic ones, are the best studied: they typically are 180–500 km in diameter, depress the pycnocline from 60 to 145 m at the eddy center, have swirl speeds in excess of 1 m s⁻¹, migrate west at velocities ranging from 11 to 19 cm s⁻¹ (with a slight southward component), and maintain a height signature of up to 30 cm. The primary generating agents for these eddies are the strong, intermittent wind jets that blow across the isthmus of Tehuantepec in Mexico, the lake district in Nicaragua and Costa Rica, and the Panama canal. Other proposed eddy-generating mechanisms are the conservation of vorticity as the North Equatorial Counter Current (NECC) turns north on reaching America, and the instability of coastally trapped waves/currents.Tropical Instability Waves (TIWs) are perturbations in the SST fronts on either side of the equatorial cold tongue. They produce SST variations on the order of 1–2 °C, have periods of 20–40 days, wavelengths of 1000–2000 km, phase speeds of around 0.5 m s⁻¹ and propagate westward both north and south of the Equator. The Tropical Instability Vortices (TIVs) are a train of westward-propagating anticyclonic eddies associated with the TIWs. They exhibit eddy currents exceeding 1.3 m s⁻¹, a westward phase propagation speed between 30 and 40 km d⁻¹, a signature above the pycnocline, and eastward energy propagation. Like the TIWs, they result from the latitudinal barotropically unstable shear between the South Equatorial Current (SEC) and the NECC with a potential secondary source of energy from baroclinic instability of the vertical shear with the Equatorial Undercurrent (EUC).This review of mesoscale processes is part of a comprehensive review of the oceanography of the eastern tropical Pacific Ocean.     

Delving into three-dimensional structure of the West Luzon Eddy in a regional ocean model

The three-dimensional structure and associated dynamics of the prominent cold (cyclonic) West Luzon Eddy (WLE) were investigated by a high-resolution regional ocean model. The WLE was horizontally and vertically heterogeneous, exhibiting asymmetric structures in the circulation, vorticity, vertical motion and energy distributions within the eddy. The asymmetry was mainly attributed to the existence of an eddy dipole formed by a coexisting warm (anti-cyclonic) eddy to the south of the WLE. Analysis of the momentum balance revealed that the coexistence of two eddies intensified barotropic pressure gradients in the southern WLE to locally enhance the eastward jet. The positive (negative) vorticity of the jet strengthened (weakened) the eddy in the southern sector (periphery), which, together with the formation of a subsurface density front, intensified (suppressed) the corresponding upward motion and cooling. The baroclinic pressure gradients opposed the dominant barotropic components and spun down the eddy at greater depths with stronger weakening in the southern sector near the front. Asymmetric energy distributions showed that larger mean kinetic energy (MKE) and eddy available potential energy (EAPE) were stored in the southern sector of the WLE. While the larger MKE was directly linked with the stronger barotropic currents, the larger EAPE in the southern WLE was formed by baroclinic energy conversions due to a strong density gradient at the front.     

南海十问

南海环流及其与世界大洋的联系带来许多重要的科学问题.本文前瞻性地提出了南海十个近期值得关注的重点研究方向,包括季风控制南海的通风问题、水团的形成和变性、海洋热盐及其质量平衡、环流能量学与海洋混合、中尺度涡、台风的海洋效应、深层海洋环流与古气候记录、南海与邻近大洋的相互作用、上升流与生态系统、以及对南海气候变化的响应.     

A two-layer simple baroclinic equation ocean model and its simulations of ocean currents in winter and summer

INTRODUCTIONThe world ocean is one of the important components of the human environment. With thedevelopment of marine resource exploit and marine engineering, more and more attention shouldbe paid to the study of ocean current movements by the means of numerical simulation and numerical prediction. It can not only improve our knowledge about the law of ocean circulation but alsocheck the reliability of theoretical research and scientific prediction. On the other hand, it canmake up for t…     

21世纪初海洋预报系统发展现状和趋势

海洋预报是一切海上活动的基础,人类社会需求驱动着海洋预报的发展。海洋观测、数据同化、数值模拟和高性能计算机等技术的进步推动着全球海洋业务预报的发展。国际先进的海洋数值模式有NLOM、NCOM、HYCOM、NEMO、MOM、POM和ROMS等。在GODAE和GODAEOceanView项目期间,通过国际合作和交流,全球海洋业务预报系统得到快速发展。21世纪初,全球海洋预报系统水平分辨率最高达到1/32°,预报时效一般为一周,部分海洋预报系统能够预报诊断海洋涡旋和海洋锋等。未来海洋预报系统的分辨率和预报精度将继续提高,预报要素扩展到海洋生态和生物地球化学等学科。海洋数据同化技术、海洋物理过程参数化方案和模式耦合技术是推动海洋预报发展的重要研究方向。     

海洋观测方法之研究

本文讨论了海洋观测技术的定义,厘清了其与海洋探测技术和海洋监测技术的关系,并在认识海洋观测数据本质的基础上,从技术性、实时性、经济性和适用性等4个方面,来讨论海洋观测方法。本文研究表明,抓着观测数据的本质保障观测数据的质量;观测手段特别是平台技术决定观测技术的实时性;实时性反映海洋观测任务的需要及观测技术的水平;经济性决定观测技术的选用;适用性进一步决定海洋观测技术的最佳形式,甚至衍生出新的观测技术。     

海洋酸化之时间序列研究进展

本文简要总结了海洋酸化时间序列研究的主要方法，重点综述了时间序列研究在揭示海洋酸化长期变化方面的重要进展。大气中 CO2 不断溶解进入海洋，导致海水 pH 与碳酸钙饱和度 （Ω） 降低，这一过程即为海洋酸化。海洋酸化时间序列研究主要关注 pH 与Ω的实时、动态、长期变化。在海洋酸化时间序列研究中，pH 一般通过锚泊浮标所搭载的传感器现场获得，而Ω则需借助相关参数间接计算得到。目前全球共有 21 套正在运行的锚泊浮标，分别布设在大洋、近岸和珊瑚礁等海域，记录了近十几年来全球典型区域海洋酸化的长期变化过程。受上升流、生产力、陆源输入等因素的协同影响，近岸海域的酸化现象极具季节/年际变化，pH 和Ω 的变化范围较大，分别为 7.780~8.723，1.07~9.25。大洋的 pH 变化范围为 7.890~8.238，珊瑚礁的 pH 变化范围为 7.837~8.273，大洋的Ω变化范围为 1.93~4.19，珊瑚礁的Ω 变化范围为 2.06~5.22。海洋酸化时间序列研究表明，受人为活动与气候变化的共同影响，北半球近岸典型海域的Ω在冬季和春季已出现低于生物耐受阈值的现象，将产生十分严重的生态危害，需要尽快采取应对措施。     

Mesoscale eddies off Peru in altimeter records: Identification algorithms and eddy spatio-temporal patterns

Relatively little is known about coherent vortices in the eastern South-Pacific along the Peruvian coast, even with regard to basic facts about their frequency of occurrence, longevity and structure. This study addresses these issues with nearly 15 years of relatively high-resolution satellite altimetry measurements.We first compare two distinct automated methods for eddy identification. The objective validation protocol shows that the rarely-used geometrical or “winding-angle method”, based on the curvature of the streamline functions, is more accurate than the commonly-used “Okubo–Weiss algorithm”, which defines a vortex as a simple connected region with values of Okubo–Weiss parameter weaker than a given threshold.We then investigate vortices off Peru using more than 20,000 mesoscale eddies identified by the winding-angle method. Coherent eddies, characterized by a high ratio of vorticity to deformation rate, are typically formed along the coast and propagate westward at 3–6 cm s⁻¹. The vortices have a mean radius of 80 km, increasing northward, and are most frequently observed off of Chimbote (9°S) and south of San Juan (15°S). The mean eddy lifetime is about 1 month, but if eddies survive at least 2 months, the probability for surviving an additional week (or month) is constant at 90% (or 67%). Anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward. In general, cyclones and anticyclones are similar, except for eddies surviving at least 6 months. In this case, after a similar 3–4 months of radius and amplitude growth, amplitudes (or sizes) decay particularly rapidly for anticyclonic (or cyclonic) eddies. In terms of intensity, cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi-constant value, whereas anticyclones exhibit steady decline. Finally, eddy temporal variations were examined at seasonal and interannual scales in the “coastal” region favorable to the formation of energetic mesoscale structures. On seasonal scales, eddy activity is maximal in fall and minimum in spring. At interannual scales, the eddy activity index was maximal during the strong El Niño of 1997–1998 but another strong maximum of eddy activity also occurred late in 2004. These temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal-trapped waves which generate baroclinic instabilities. Further investigation of the mechanisms involved on the eddy genesis is needed.     

逆式回声测量仪在全球海洋中应用及前景展望

系统总结了逆式回声测量仪(IES)的发展历史,重点介绍了其目前在世界范围内的应用情况,并阐述了CPIES(集成流速和压力传感器的IES)在我国吕宋海峡周边布放的意义及对未来应用的展望。结果表明采取不同的排列方式布放的IES阵列所获取的数据通过结合地转经验模态GEM (gravest empirical mode)以及最优插值方法能够获得观测海区的温度、盐度和流场的三维空间分布特征。基于CPIES的应用,可深入地研究多尺度的海洋动力过程,如内波、内潮和中尺度涡等,对后续大洋环流理论发展、中尺度涡产生和消亡机理、海洋中不同尺度能量串级等具有重要意义。     

上层海洋对热带气旋的响应与反馈研究进展

对60年来有关上层海洋与热带气旋(Tropical Cyclone,TC)的响应与反馈的研究进行了回顾,通过观测手段的完善和改进模式的应用,人们的认识不断提高:TC直接激发的近惯性流最大可达1 m/s,其导致的强烈的剪切造成混合层对下层冷水的夹卷是引起混合层降温的主要原因,并往往伴随着混合层深度的增加,这一影响在TC右侧更为最著,并可延续几天到几十天不等。TC导致的混合层降温会使得海洋输出的热通量减少,反过来削弱TC的强度,形成一个负反馈,而海洋特殊的热力和环流结构(如暖涡、洋流等)则对TC有正反馈。所以了解TC经过前的海洋初始场对研究TC与海洋之间的相互作用、对预测,TC的强度、路径变化等尤其重要;通过准确的初始场结合越来越完善的模式可以对TC进行更真实的模拟和预测,使得对TC准确的预报和预警成为可能。     

The role of surface waves in the ocean mixed layer

Previously, most ocean circulation models have overlooked the role of the surface waves. As a result, these models have produced insufficient vertical mixing, with an under - prediction of the ,nixing layer （ML） depth and an over - prediction of the sea surface temperature （SST）, particularly during the summer season. As the ocean surface layer determines the lower boundary conditions of the atmosphere, this deficiency has severely limited the performance of the coupled ocean - atmospheric models and hence the climate studies. To overcome this shortcoming, a new parameterization for the wave effects in the ML model that will correct this systematic error of insufficient mixing. The new scheme has enabled the mixing layer to deepen, the surface excessive heating to be corrected, and an excellent agreement with observed global climatologic data. The study indicates that the surface waves are essential for ML formation, and that they are the primer drivers of the upper ocean dynamics; therefore, they are critical for climate studies.     

Estimating the underwater light field from remote sensing of ocean color

We present a new approach that incorporates two models to estimate the underwater light field from remote sensing of ocean color. The first employs a series of analytical, semi-analytical, and empirical algorithms to retrieve the spectrum of inherent optical properties (IOPs), including the absorption and the backscatter coefficients, from the spectrum of remote sensing reflectance. The second model computes the profile of photosynthetically available radiation E _0,PAR (z) for a vertically homogeneous water column using the information of the retrieved IOPs and the ambient optical environment. This computation is based on an improved look-up table technology that possesses high accuracy, comparable with the full solution of the radiative transfer equation, and meets the computational requirement of remote sensing application. This new approach was validated by in situ measurements and an extensive model-to-model comparison with a wide range of IOPs. We successfully mapped the compensation depth by applying this new approach to process the SeaWiFS imagery. This research suggests that E _0,PAR (z) can be obtained routinely from ocean-color data and may have significant implications for the estimation of global heat and carbon budget.     

POLDER水色大气校正算法研究

基于POLDER多角度观测数据,对其大气校正算法进行了研究。该大气校正算法中,大气分子散射利用多次散射加偏振的精确瑞利散射来计算,同时,对太阳耀斑及白帽散射进行了校正。由本文大气校正算法可以反演得到气溶胶光学厚度以及海水反射率,与POLDER二级产品相比表明,利用该算法反演所得产品效果较好,相对误差在10%左右,从而为未来中国多角度水色遥感的发展提供一些参考。     

Living on the edge: feeding of subtropical open ocean copepods

The objective of this study was to provide quantitative information on environmental feeding rates of warm water oceanic epipelagic copepods. We determined clearance rates at 23 °C for various particle size ranges in shipboard studies in the western oligotrophic subtropical Atlantic Ocean for females of the calanoid species Clausocalanus furcatus and Mecynocera clausii. These in situ clearance rates were then applied to the various particle size ranges of environmental particle spectra of auto‐ and heterotrophs at different depths from three stations in the western Atlantic. After calculating the metabolic demands of each of these two copepod species and applying an assimilation efficiency of 90%, we determined that C. furcatus meets its metabolic demands in all six cases, and M. clausii in two of six cases. Clausocalanus furcatus would also meet its energy demands at 25 °C, where it is often found, while M. clausii at 20 °C, where it is regularly found, would cover its metabolic needs in four of six cases. It is hypothesized that these species, and most likely most of the other co‐occurring copepod species, are limited in their abundance by food availability, or, better said, are ‘living on the edge’ in relation to food abundance.     

Satellite and in situ observations of the bio-optical signatures of two mesoscale eddies in the Sargasso Sea

Satellite ocean-color imagery and field spectroradiometer observations are used to assess the bio-optical signatures of two mesoscale features, a cyclone C1 and an 18°-water anticyclone A4, in the Sargasso Sea. Field determinations of upper layer bio-optical properties, such as the diffuse attenuation coefficient and remote-sensing reflectance spectra, show little statistically significant variations with distance to the eddy center for either eddy. This contrasts field observations showing many-fold higher phytoplankton pigment biomass at depth (and for A4 higher primary production rates at depth) than is typical for this region. The cyclone C1 does show a significant decrease in the depth of the 1% photosynthetically available radiation (PAR) isolume with increasing distance from eddy center while the anticyclone A4 shows no coherent signal vs. distance. Vertical profiles of bio-optical properties show consistent patterns where subsurface maxima are displaced higher inside the core of the cyclone C1 than in the surrounding waters while the highest values of the diffuse attenuation coefficient at 443 nm are observed within the core of anticyclone A4. Satellite observations of near-surface bio-optical properties show signals consistent with eddy physical characteristics, although the magnitude of these variations is very small, barely detectable by typical field measurement protocols. Mean values of bio-optical properties are higher within the cyclone compared with its periphery but not for the anticyclone. For both eddies, significant inverse correlations are observed between time series of bio-optical properties and eddy center sea-level anomaly. Consistent response to wind speed is also noted: following strong wind events, bio-optical parameters are elevated inside the anticyclone and are reduced inside the cyclone. These observations demonstrate that a combination of physical processes, including vertical eddy uplift, eddy horizontal advection, and eddy-scale Ekman pumping, contribute to the bio-optical imprint of mesoscale eddies. The contributions of these forcing mechanisms change over the period of observation, illustrating the limitations of inferring eddy bio-optical dynamics from short-term, field observations. The present analyses provide insights into the potential as well as the drawbacks of bio-optical techniques for probing the biological and biogeochemical impacts of open-ocean eddies.     

中国“数字海洋”原型系统构建和运行的基础研究

1 引言 "数字海洋"伴随"数字地球"战略的提出应运而生,是"数字地球"十分重要的组成部分,是"数字地球"理论和技术在海洋工作领域的体现和再创新[1-5].国外与"数字海洋"相关的研究主要包括全球海洋观测系统(GOOS)、基于遥感技术的全球海平面上升研究、区域性海洋观测如信息服务系统等,比较典型的有GOOS,美国的改善海洋观测系统(IOOS)、澳大利亚的BLUELINK等系统[6-9].     

海洋微塑料检测技术研究进展

海洋微塑料污染目前已成为全球性的环境问题,近年来海洋微塑料检测技术越来越受到人们的关注。本文简要总结了微塑料样品采集及处理方法,并从检测方法的角度系统综述了近些年来微塑料检测技术的研究进展,涉及目视分析法、光谱法(如傅立叶变换红外光谱法和拉曼光谱法)、热分析法以及其他分析方法等(如质谱法以及扫描电子显微镜-能谱仪联用法)。本文简要评价了各类检测方法的优缺点,以期为海洋微塑料检测技术的发展提供参考,并探讨了未来海洋微塑料检测技术的发展方向。     

层化海洋中的二阶波散射作用问题

引入Stokes有限振幅水波的多色波作用机制 ,采用二层层化海洋模型 ,分析了层化海洋中非线性波对结构的散射作用问题。提出了二层海洋中二阶水波散射条件的数学表达式 ,进而推导了二层海洋中二阶波对一般型圆柱散射作用的格林积分解式 ,并给出了对解式中自由面及分层界面无限积分的递推算式。     

海洋标准评估方法研究

科学评估海洋标准是提高海洋标准质量的重要手段.分析了影响海洋标准评估因素确定的条件,建立海洋标准评估指标体系与评价集.利用层次分析法和模糊综合评价法对海洋标准进行评估,定量评估了海洋标准的质量.该方法为建立科学的、操作性强的标准评估体系提供研究基础,有利于完善对海洋标准质量的控制,提高海洋标准的管理水平.     

分层流体中细长体波浪力的数值计算

利用边界元法计算了层化流体中细长体受到的一阶垂荡波浪力和一阶纵摇波浪力矩，计算了近水面细长体的波浪力及力矩，与水池实验结果相吻合。