ENSO相联系的热带太平洋上层海洋异常环流

本文使用SODA(simple ocean data assimilation)海洋同化资料,系统分析了厄尔尼诺-南方涛动(El Ni?o-Southern Oscillation,ENSO)循环中冷暖位相期间热带太平洋上层海洋环流的演变规律,探讨了形成海洋环流异常的新机制。结果表明,在厄尔尼诺成熟期,热带中东太平洋赤道潜流最弱,赤道两侧出现反气旋性环流异常;西太平洋赤道外热带海域出现气旋性环流异常,该区南、北赤道流、棉兰老流、黑潮、新几内亚沿岸潜流及南赤道逆流增强;北赤道逆流区出现异常气旋性环流串,北赤道逆流接近正常。在厄尔尼诺衰退期和拉尼娜发展期,热带中西太平洋赤道潜流达到极强,赤道两侧出现气旋性环流异常;西太平洋赤道外热带海域异常环流减弱,该处主要流场的强度减弱或处于正常状态;北赤道逆流区反转为异常西向流。结果表明, ENSO循环期间的上层海洋环流异常受到热带太平洋温跃层深度异常产生的压强梯度力异常调控,在赤道外热带海洋温跃层深度异常和科里奥利力共同作用产生大尺度海洋环流异常,而在赤道海域,海洋温跃层深度异常和Gill效应造成赤道潜流异常以及关于赤道对称的气旋或反气旋性环流异常。     

主流系与西太平洋暖池变异机制研究进展

中国科学院战略性先导科技专项重点任务2以热带西太平洋主流系和暖池为主要研究对象,基于西太平洋和印尼海科学观测网综合观测数据,结合动力理论分析和数值模拟结果,在主流系和西太暖池的三维结构、变异规律和动力机制,以及西太与周围海域之间物质能量交换等方面取得了原创性成果。在上层主流系和暖池变异方面,首次直接观测到棉兰老潜流(MUC)、吕宋潜流(LUC)和北赤道潜流(NEUC)等次表层潜流及其多尺度变异,给出了三支潜流相互间的水源关系,揭示了潜流系统强劲的季节内变化特征及其与中尺度涡旋活动的关系,并进一步分析了棉兰老流(MC)/MUC年际变异及其控制因素。西太平洋主流系平流输送在暖池形成中起到了主要作用,而且暖池北部区域自20世纪90年代起出现显著的扩张现象,是由混合层厚度变浅导致。在中深层环流特征和机制方面,发现南北半球中层水团的交换通道、机制和显著交换周期;丰富了对赤道西太平洋中层流结构特征和变异的认识,同时突破了对西太平洋深层环流结构特征和变异规律的认知局限,例如中深层流流速自北向赤道增加,其变化远大于平均值,菲律宾海盆中部深层流以西南-东北方向为主,赤道区域中深层流以纬向东西交替的射流为主等。在西太与周围海域之间物质能量交换方面,通过在印尼贯穿流(ITF)源区及印尼海的同步走航及定点潜标观测,揭示了MC在苏拉威西海和马鲁古海峡交汇处的流径跃变在2015—2016超强El Ni?o的发生起重要作用,西边界流区的非线性反射对ENSO事件的发生发展起至关重要的作用。上述原创性成果显著提升了热带西太平洋环流动力学的认知水平。     

数据报告：布莱克海台997站位晚中新世至更新世的硅藻

ODP997站位位于大西洋布莱克海台上。布莱克海台的海底沉积受到墨西哥湾流和西部边界潜流的极深影响,其上覆亚热带中心旋回的外围海水,暖盐的墨西哥湾流和西部边界潜流（WBUC）搬运了大量的碎屑沉积物到布莱克海台形成泥砂漂移（图1）。船上超微化石分析和沉积物粒度分析发现：沉积速率随深度增加呈增加趋势,三个层位的硅藻丰度有显著高异常（Shipboard Scientific Party,1996）。因此,研究地层中硅藻堆积速率变化对于了解这一地区的古海洋学和沉积史是非常重要的。     

垂直混合方案对全球海洋环流模式模拟结果的影响对比研究

利用Modular Ocean Model version4(MOM4)海洋环流模式设计了2个全球海洋-海冰耦合的数值实验,以分析比较Pacanowski and Philander(PP)和K-Profile Parameterization(KPP)两种不同垂直混合方案在全球海洋上层模拟中的表现。实验结果表明,PP和KPP方案在中纬和高纬海域模拟海温差别较大,后者模拟结果好于前者;在低纬海域差别较小,但赤道断面PP方案模拟结果较好;KPP方案能很好地模拟太平洋赤道潜流,而PP方案模拟的赤道潜流位置偏浅。     

赤道太平洋的环流

一.引 言 赤道太平洋上层海洋环流的主要特征已被建立十多年了。1942年斯维尔德鲁普等人描述了中太平洋的表面流:往西流的北和南赤道流以及往东流的北赤道逆流。随后,南赤道逆流也被用表面动力高度图表示出来(Reia,1961),Cromwell等人(1954)发现了赤道潜流,从而对上述环流的描述进行了主要修正。Hisard和Rual(1970)发现了赤道潜流下面     

印度洋上层经向翻转环流的冬夏季节对比

上层经向翻转环流(shallow meridional overturning circulation, SMOC)主导热带-副热带上层海洋水体交换,对海洋物质输运和热量交换具有重要意义。基于7套海洋再分析数据产品,本文主要探讨了印度洋SMOC的冬夏季节变化及其差异的原因。结果显示,印度洋SMOC主要由南半球副热带环流圈(southern subtropical cell, SSTC)和跨赤道环流(cross-equatorial cell, CEC)组成,并且具有显著的季节差异。夏季风期间, SSTC和CEC均为表层南向输运,表层以下北向输运的逆时针环流结构。冬季风盛行时, SSTC仍维持逆时针结构,但环流中心南移且深度加深,强度弱于夏季;然而, CEC却转向为表层北向输运,表层以下向南输运的顺时针环流结构,其环流中心位置与夏季接近,环流强度与夏季相当。这种印度洋SMOC冬夏结构差异究其原因主要由风生环流主导, CEC冬夏季节环流方向反转是北印度洋冬夏季风转向的结果,而南印度洋信风的季节性位移和强度变化是SSTC强度和位置季节差异的主要原因。     

“海洋环流与海气相互作用重点研究实验室”在中科院海洋所成立

中国科学院海洋研究所为积极投入到世界海洋科学研究三大前沿领域——热带海洋与全球大气(TOGA)、世界大洋环流实验(WOCE)、全球海洋通量研究(JGOFS),集中了本所物理海洋学研究的优势力量,成立了“海洋环流与海气相互作用重点研究实验室”。该研究室的研究方向是,跟踪世界海洋学研究前沿,重点研究海洋环流和海洋在气候变化中的作用;研究内容是,研究南太平洋赤道流系(包括赤道流、北赤道流、北赤道逆流和赤道潜流)的结构及其变化机制,重点研究北赤道流在菲律宾海南部的分支过程和南部     

黑潮源区次表层的低频季节内变化

根据黑潮源区吕宋岛附近(18°N,122.5°E)投放的ADCP测得的流速,发现次表层流动与海表黑潮(Kuroshio,KC)流动并不一致,除了流动方向不同外,次表层吕宋潜流(Luzon Undercurrent,LUC)在500~1000 m深度存在一个低频季节内周期变化(120 d),这一变化并非由海表黑潮的季节性变化引起。针对这一现象,结合混合坐标海洋模式(Hybrid Coordinate Ocean Model,HYCOM)数据,使用涡动能(Eddy Kinetic Energy,EKE)分析并追踪100~200 d周期温盐和流速变化异常,最终得出结论:吕宋潜流季节内变化存在两个频率的周期,较高频季节内变化(80 d)是由表层黑潮区的中尺度涡传递到次表层产生的,而低频季节内变化(100 d以上)由136°E附近的中尺度涡旋经过6~7个月的运动到达吕宋岛沿岸产生的。     

南海海洋环流季节变化的数值模拟研究

基于POM(Princeton Ocean Model)海洋模式,对南海不同深度环流的季节性变化进行了数值模拟研究。模拟结果表明:南海表层和上层环流受季风影响,在夏季西南季风驱动下,南海表层环流在南部呈现强反气旋式结构,在南海北部则是一个弱的气旋环流;在冬季东北季风驱动下,南海表层环流结构呈气旋式,并且明显加强了沿越南沿岸向南流动的西边界流;春季和秋季为南海季风的转换期,其对应的环流特征也处于冬季环流与夏季环流的过渡流型,流速与冬季和夏季相比较弱。南海200m层环流的季节变化与表层相似。在500与1 000m层,则出现许多处中尺度漩涡,流场也变得较为紊乱。     

热带太平洋平均环流数值模拟

用中国科学院大气物理研究所发展的高分辨率自由表面热带太平洋环流模式(区域为南北纬30°,经纬圈方向水平分辨率分别为1°和2°,垂直方向分为不等距14层),在观测到的海表面风应力和热量及淡水通量驱动下,对热带太平洋平均环流进行了数值模拟.结果表明,模式成功地模拟了海面起伏中赤道槽、赤道脊、北赤道逆流槽及中小尺度涡旋(如棉兰老涡)系统等分布;与这些槽脊分布相对应的北赤道流,南赤道流和北赤道逆流等热带流系;对气候有重大影响的海表温度分布;次表层温跃层结构和赤道潜流等.文中特别讨论了海面起伏与模式其他变量场间的关系及其应用.     

赤道太平洋温度、流场距平EOF分析及与厄尔尼诺的关系

利用EOF分析方法,讨论了最近20a赤道太平洋次表层温度、纬向流距平与厄尔尼诺的关系.结果表明:赤道太平洋海温距平EOF分析第一、二主分量占总量的近80%,其中第一主分量类似于厄尔尼诺模态,第二主分量类似于暖池模态;后一模态存在着突变和渐变两种过程,其中由冷位相变暖位相过程为渐变过程,而暖位相变冷位相过程为突变过程.厄尔尼诺事件是赤道西太平洋暖池突变过程的结果.赤道太平洋纬向流距平EOF的第二主分量代表赤道西太平洋潜流和东太平洋南赤道流的变化,这个模态存在着半年左右的振荡和与厄尔尼诺同位相的年际振荡两种频率.另外,它还存在明显的年代际变化.赤道西太平洋潜流和东太平洋南赤道流减弱是产生厄尔尼诺的必要条件.统计回归分析表明,赤道太平洋海温距平和纬向流距平EOF的第二特征向量的时间系数对厄尔尼诺和拉尼娜均有一定的预报意义.     

赤道潜流变化及其与ENSO的关系

应用TOGA/TAO实测海流和SODA全球海洋再分析资料,分析研究了热带太平洋赤道潜流的变化特征及其与ENSO循环的关系,初步探讨了赤道潜流变化对两种不同类型(中部型和东部型)ENSO事件的影响。对赤道潜流距平场的EOF分解表明,第一模态为"东太平洋潜流模态",特征向量主要反映东太平洋赤道潜流的变化情况;第二模态为"中太平洋潜流模态",特征向量主要反映中太平洋赤道潜流的变化情况;这两个主要模态基本可以反映赤道潜流距平场的主要信息。这两个模态对应的时间系数有明显的年际变化特征,并且与NINO指数都有较好的负相关,最大相关均通过99.9%的信度检验。相关分析表明潜流第一模态的变化滞后于NINO指数变化,而第二模态的变化则提前于NINO指数变化,即ENSO事件对东太平洋赤道潜流的变化有一定影响,而中太平洋的潜流变化又会对ENSO事件产生影响。通过个例分析表明,中太平洋赤道潜流的变化对两种不同类型ENSO事件的发生有重要影响。在东部型ENSO事件发生前,中太平洋赤道潜流增强,这样西太平洋暖池的异常海温在潜流的引导下快速向东传播,直接到达东太平洋形成东部型ENSO事件;中部型ENSO事件发生前,中太平洋赤道潜流明显减弱,西太平洋的异常海温不能迅速东传速,在中太平洋堆积上升到达海面,使得中部型ENSO事件爆发。     

印度洋赤道潜流年际变化特征及其与印度洋偶极子的联系

印度洋赤道潜流(equatorial undercurrent,EUC)是赤道流系的重要组成部分,对印度洋物质输运和能量交换有着重要意义.基于SODA 3.4.2海洋再分析数据,对印度洋EUC的三维空间结构和年际变化特征进行分析,并揭示其年际变率与印度洋偶极子(Indian Ocean dipole,IOD)的联系.结...     

An analysis of bomb radiocarbon trends in the Pacific

The post-nuclear time-series curves of Δ¹⁴C from corals at different locations in the surface of the Pacific Ocean show a variation in the shape, amplitude and timing of the peak, with the subtropical records peaking first, followed by the western, and then eastern tropical records with lower maxima. This work takes an in-depth look at the processes that shape the time histories of Δ¹⁴C in surface waters at different locations in the Pacific. A one-dimensional (1-D) model is used to examine whether convection and diffusion can delay the peaking of the Δ¹⁴C time series. Using the three-dimensional (3-D) MIT general circulation model (GCM), the distribution and evolution of Δ¹⁴C is simulated “offline” from 1955 onwards at 1° resolution globally. The GCM is used to tease apart the contribution of various processes, viz. advection, air–sea flux, convection and diffusion, to altering the Δ¹⁴C content of surface waters at different locations in the Pacific. A time history of ¹⁴C column inventories from the model is constructed to examine the role of horizontal advection in supplying tropical locations with ¹⁴C much after the peak atmospheric flux. This model analysis supports the idea of ¹⁴C-rich waters from the subtropics being transported to the western tropics via the subsurface, and then being advected eastward in the equatorial undercurrent and upwelled in the east.     

Numerical simulations of the Mediterranean sea outflow: impact of the entrainment parameterization in an isopycnic coordinate ocean model

Gravity current entrainment is essential in determining the properties of the interior ocean water masses that result from marginal sea overflows. Although the individual entraining billows will be unresolvable in large-scale ocean models for the foreseeable future, some large-scale simulations are now being carried out that do resolve the intermediate scale environment which may control the rate of entrainment. Hallberg [Mon. Wea. Rev. 128 (2000) 1402] has recently developed an implicit diapycnal mixing scheme for isopycnic coordinate ocean models that includes the Richardson number dependent entrainment parameterization of Turner [J. Fluid Mech. 173 (1986) 431], and which may be capable of representing the gravity current evolution in large-scale ocean models. The present work uses realistic regional simulations with the Miami Isopycnic Coordinate Ocean Model (MICOM) to evaluate ability of this scheme to simulate the entrainment that is observed to occur in the bottom boundary currents downstream of the Mediterranean outflow. These simulations are strikingly similar to the observations, indicating that this scheme does produce realistic mixing between the Mediterranean outflow and the North Atlantic Central Water. Sensitivity studies identify the critical Richardson number below which vigorous entrainment occurs as a particularly important parameter. Some of these experiments also show meddies detaching from the Mediterranean undercurrent at locations that appear to be highly influenced by topographic features.     

THE DIAGNOSTIC CALCULATION OF EQUATORIAL FLOWS IN THE EASTERN PART OF THE WESTERN PACIFIC OCEAN

On the basis of observational data of the eastern part of the West Pacific Ocean, a diagnostic calculation of equatorial flow for this region is performed by using the authors' model equations and computing scheme and methods. For the first cruise (January 3-March 4, 1979), the results show: (i) The primary driving force of the equatorial surface flows comes from the prevailing northeasterly wind field, with an average uniform wind speed Vw = 6.3 m/s. The steady westward wind produces divergent westward flows in the surface layers, causing an upwelling near the equator. The importance of the steady wind stress in the upper layer (120 m) decreases with depth and becomes insignificant at the level of z = 75 m or z = 100 m, (ii) The equatorial undercurrent is a strong eastward and equator-ward flow, with its eastward component of undercurrent larger than its meridional component. The core of the undercurrent is at the thermocline, and its maximum velocity is 88-90 cm/s at the level of z=200 m. The deeper f     

Manifestations of the Black Sea undercurrent in the density and hydrostatic pressure fields

Vertical kinematic structure of the geostrophic currents has been found to be correlated to the distribution of seawater density and hydrostatic pressure over depth. The conditions necessary for the existence of the undercurrent have been defined. On this basis, hydrological survey data compiled by the Marine Hydrophysical Institute in the Black Sea have been treated. Examples are given, which support theoretical deductions about the possible existence of the undercurrent beneath the Black Sea rim current. The undercurrent's parameters have been determined, along with the depths of the upper and lower boundaries and the mainstream velocity. Translated by Vladimir A. Puchkin.     

热带西太平洋潜流模拟:(Ⅰ)模式配置与模拟结果验证

利用高分辨率准全球海洋模式HYCOM(HYbrid Coordinate Ocean Model),采用局部加密网格的方法,模式积分30年,模拟了热带西太平洋环流的年平均状态和季节变化.通过与实测的海表面高度、测流资料、温盐资料等对比分析,验证了模拟结果的有效性,认为模式结果可以用于研究热带西太平洋潜流及其季节变化.     

The mesoscale variability in the Caribbean Sea. Part II: Energy sources

The processes which drive the production and the growth of the strong mesoscale eddy field in the Caribbean Sea are examined using a general circulation model. Diagnostics of the simulations suggest that:(1) The mean currents in the Caribbean Sea are intrinsically unstable. The nature of the instability and its strength vary spatially due to strong differences of current structure among basins.(2) The greatest and most energetic eddies of the Caribbean Sea originate in the Venezuela Basin by mixed barotropic-baroclinic instability of an intense jet, formed with waters mostly from the surface return flow of the Meridional Overturning Circulation and the North Equatorial Current which converge and accelerate through the Grenada Passage. The vertical shear of this inflow is enhanced by an eastward undercurrent, which flows along the south American Coast between 100 and 250 m depth. The shallow eddies (less than 200 m depth) formed in the vicinity of the Grenada Passage get rapidly deeper (down to 1000 m depth) and stronger by their interaction with the deep interior flow of the Subtropical Gyre, which enters through passages north of St. Lucia. These main eastern Caribbean inflows merge and form the southern Caribbean Current, whose baroclinic instability is responsible for the westward growth and strengthening of these eddies from the Venezuela to the Colombia Basin.(3) Eddies of lesser strength are produced in other regions of the Caribbean Sea. Their generation and growth is also linked with instability of the local currents. First, cyclones are formed in the cyclonic shear of the northern Caribbean Current, but appear to be rapidly dissipated or absorbed by the large anticyclones coming from the southern Caribbean. Second, eddies in the Cayman Sea, which impact the Yucatan region, are locally produced and enhanced by barotropic instability of the deep Cayman Current.(4) The role of the North Brazil Current (NBC) rings is mostly to act as a finite perturbation for the instability of the mean flow. Their presence near the Lesser Antilles is ubiquitous and they appear to be linked with most of the Caribbean eddies. There are some evidences that the frequency at which they form near the Grenada Passage is influenced by the frequency at which the NBC rings impinge the Lesser Antilles. But large Caribbean eddies also form without a close influence of any ring, and comparison between simulations shows that mean eddy kinetic energy and eddy population in the Caribbean Sea are not substantially different in absence or presence of NBC rings: their presence is not a necessary condition for the generation and growth of the Caribbean eddies.