不同时间尺度系统对热带太平洋海-气潜热通量贡献的估计

对热带太平洋不同尺度系统对海洋大气之间潜热通量的贡献进行了计算分析。分析使用了Launianen和Vihma(1990)依据相似理论编写的计算软件和TOGA-TAO观测资料。通过分析发现，小尺度系统对热量通量没有太多的影响；天气尺度系统在赤道西太平洋对热量通量的影响较大；天气尺度系统对热量通量的贡献在赤道外地区要比在赤道地区大。分析还发现，在厄尔尼诺年赤道中太平洋地区天气尺度系统对热量通量的贡献较大，这意味着赤道中太平洋天气尺度系统的活动对触发厄尔尼诺事件可能具有重要的影响。     

赤道深层急流动力机制初步探讨

多年现场观测揭示,在大洋深层许多区域存在出人意料的高能区,诸如在赤道1000～3000m深度间存在着东西流向随深度交替变化的急流,本文提出连系不同密度水体输运的局部浮力振荡所产生的波动以及关连的能量辐射和沿赤道产生的局部能量辐聚是形成赤道深层急流的主要动力机制.本文结果还揭示,铅垂向湍粘系数和湍扩散系数的大小与赤道深层急流的结构和强度间存在密切的关系.对应大的铅垂向湍粘系数和湍扩散系数,急流强度减弱且其纬向相干尺度和铅垂尺度增大.另外不同周期的浮力振荡产生不同结构和强度的急流.振荡周期越长,急流的核心位置离东边界越远、沿赤道的相干尺度也越大.     

北半球越赤道气流对南半球低纬扰动的激发作用

众所周知,某一半球大型天气系统的明显变化,往往会导致另一半球环流的重大变化.早在20世纪初,李宪之就指出了南半球冷空气爆发对北半球台风发展的重要作用.近年来,黄土松等1)、2),[1]进一步研究了南半球越赤道气流对北半球季风、信风变化的影响.本文利用1984年12月-1985年2月的850hPa、200hPa格点风资料,以及同时期的卫星云图、天气图等,分析了北半球越赤道气流活动特征及其对南半球低纬扰动的激发作用.     

冬季山东南部沿海水温10—20天的周期性振动

使用谱分析和数字滤波等方法,对山东南部沿海冬季的日平均水温、水位、海平面气压和风场等历史资料(1973—1983)做了分析。结果发现,这里的水温和水位存在10—20天的振动,这种振动与同期气压场和沿岸风的振动相同,陆架水温和水位的这种天气尺度振动恰好是对冬季风强迫的响应。为证明这一物理过程,设计了一个简单的线性理论模式,并用Laplace变换获得了其解析解,证明了上述响应的物理机制。     

赤道太平洋海温的东西振荡及其模拟

本文对137°E剖面不同深度的海温资料进行了比较细致的整理和分析,发现热带西太平洋海温敏感区(约在6°N,125～150m处)的海温(WSST)与赤道东太平洋海温之间存在着明显的反位相变化关系.在对赤道太平洋海、气运动的基本特征进行分析的基础上,设计了一个简单的二维海气耦合模式.用此模式模拟出在赤道太平洋中存在一类似于大气中Walker环流的赤道太平洋环流,其强弱变化造成了赤道太平洋海温的东西振荡.     

1997/1998年厄尔尼诺期间西太平洋热带对流区的东移

1997年5月至1998年春季,发生了本世纪以来最强的厄尔尼诺事件.全球许多地区的天气气候出现了显着的异常特征,并诱发了一系列的旱、涝及森林大火等重大灾害,引起了许多国家政府和社会各界的高度关注.厄尔尼诺事件的成因和影响是一个十分复杂的问题,尽管自1950年以来已先后出现过10多次,气象和海洋学家对此也作了大量研究,但迄今对它的认识依然相当有限.对它的成因,近些年来许多研究认为[1,2]:赤道东太平洋的强偏东信风,将洋面表层暖水吹向西太平洋赤道地区堆积形成暖池;由于某种原因,一旦偏东信风张驰(减弱),导致暖池中位能释放,暖水向东回流,赤道东太平洋洋面温度(SST)异常升高,厄尔尼诺发生.     

东太平洋赤道海温变异与山东半岛花生产量

一、前言花生是山东的主要农作物之一.在全国也占重要地位.而在小麦、花生、玉米、番薯四种主要作物中,花生是受气象因素(尤其是农业热量因子)影响较显著的作物.东太平洋赤道海区,是大尺度海气相互作用最敏感的海区之一,也是对我国东部天气气候(特别是温度和降水)有显著影响的遥相关区.本文仅以10℃累积温度、气温和花生产量为例,分析了东太平洋赤道海温对我国东部农业影响的可能性,以期得到通过东太平洋赤道海温,研究农业热量和农作物产量变化规律及预报方法的新途径.     

西太平洋近赤道地区风场的变化与埃尔尼诺

本文利用综合海洋大气资料(COADS)分析了西太平洋赤道地区风场的变化与埃尔尼诺的关系,发现埃尔尼诺发生前该地区纬向风有持续的东风距平,经向上有由赤道吹向高纬的经向风异常,造成了西高东低和赤道低两侧高的海平面分布.而在埃尔尼诺年该地纬向为西风距平,经向有由高纬指向赤道的经向风异常,造成暖水在赤道附近堆积.由此产生的开尔文波是东太平洋海面温度(以下简称海温)变暖的重要原因.特别值得指出的是,在埃尔尼诺年西太平洋赤道地区两次西风距平的峰值,两次由北向南的越赤道气流和两次近赤道台风的高潮对应于东太平洋海温的两个正距平高峰.     

地球系统模式FIO-ESM对2016-2017年La Ni(n)a事件及其对中国近海地区影响的预测

最近的观测表明赤道太平洋中部及东部的水温略低于拉尼娜事件的阈值,但大气与海洋的状态还不足以完全支持转为弱拉尼娜现象.本研究基于地球系统模式FIO-ESM和集合调整卡尔曼滤波同化方案建立的短期气候同化和预测系统,进行了1992-01-01-2016-10-31的模式同化,结果表明同化系统能够为预测提供较好的初始场.随后对2016-2017年拉尼娜事件的状态以及中国近海地区气温和降水异常进行了未来6个月的预测,结果表明赤道太平洋会在2016年年底继续降温,Ni(n)o3.4区海温异常将持续略低于拉尼娜事件的阈值-0.5 ℃,说明2016-2017年为弱拉尼娜事件,2017年春季东太平洋继续降温,表明此次拉尼娜事件可能会持续较长时间.预测结果同时也表明2016年冬季至2017年春季中国近海地区存在着北高南低的气温异常分布,中国南部地区降水存在负异常.拉尼娜带来的极端天气与气候异常会对中国沿岸地区带来巨大影响,但总体来说2016-2017年拉尼娜事件对中国的影响相对较弱.     

西风爆发、次表层暖水东移与厄尔尼诺现象

利用最近20 a的大气海洋资料,分析了厄尔尼诺事件与赤道太平洋西风异常以及赤道太平洋次表层海温之间的关系.结果表明,赤道西太平洋(5°S～5°N,120°～160°E)和赤道中东太平洋(5°S～5°N,160°E～160°W)西风异常都存在着与厄尔尼诺周期一致的年际变化,但前者还包含有显著的2～3个月季节内振荡.赤道西太平洋次表层冷暖水东移也呈现年和年际时间尺度的振荡周期.在厄尔尼诺发生前,赤道西太平洋次表层海水出现持续性增暖,赤道西太平洋西风异常频率加快,强度增强.随后赤道中太平洋(160°E～160°W)出现持续性(3个月以上)强西风异常(即西风爆发),并进一步向东扩展,同时次表层暖水沿着赤道波导东移到赤道东太平洋混合层,导致赤道东太平洋海表大面积异常增暖,形成一次厄尔尼诺现象.最后,模式模拟了1980～1984年赤道太平洋海温的变化,进一步证实了赤道纬向西风异常对暖水东移起着重要的作用.     

On the parameterisation of oceanic sensible heat loss to the atmosphere and to ice in an ice-covered mixed layer in winter

In high-latitude oceans with seasonal ice cover, the ice and the low-salinity mixed layer form an interacting barrier for the heat flux from the ocean to the atmosphere. The presence of a less dense surface layer allows ice to form, and the ice cover reduces the heat loss to the atmosphere. The ice formation weakens the stability at the base of the mixed layer, leading to stronger entrainment and larger heat flux from below. This heat transport retards, and perhaps stops, the growth of the ice cover. As much heat is then entrained from below as is lost to the atmosphere. This heat loss further reduces the stability, and unless a net ice melt occurs, the mixed layer convects. Two possibilities exist: (1) A net ice melt, sufficient to retain the stability, will always occur and convection will not take place until all ice is removed. The deep convection will then be thermal, deepening the mixed layer. (2) The ice remains until the stability at the base of the mixed layer disappears. The mixed layer then convects, through haline convection, into the deep ocean. Warm water rises towards the surface and the ice starts to melt, and a new mixed layer is reformed. The present work discusses the interactions between ice cover and entrainment during winter, when heat loss to the atmosphere is present. One crucial hypothesis is introduced: “When ice is present and the ocean loses sensible heat to the atmosphere and to ice melt, the buoyancy input at the sea surface due to ice melt is at a minimum”. Using a one-dimensional energy-balance model, applied to the artificial situation, where ice melts directly on warmer water, it is found that this corresponds to a constant fraction of the heat loss going to ice melt. It is postulated that this partitioning holds for the ice cover and the mixed layer in the high-latitude ocean. When a constant fraction of heat goes to ice melt, at least one deep convection event occurs, before the ice cover can be removed by heat entrained from below. After one or several convection events the ice normally disappears and a deep-reaching thermal convection is established. Conditions appropriate for the Weddell Sea and the Greenland Sea are examined and compared with field observations. With realistic initial conditions no convection occurs in the warm regime of the Weddell Sea. A balance between entrained heat and atmospheric heat loss is established and the ice cover remains throughout the winter. At Maud Rise convection may occur, but late in winter and normally no polynya can form before the summer ice melt. In the central Greenland Sea the mixed layer generally convects early in winter and the ice is removed by melting from below as early as February or March. This is in agreement with existing observations.     

海浪破碎对海洋上混合层中湍能量收支的影响

海浪破碎产生一向下输入的湍动能通量,在近海表处形成一湍流生成明显增加的次层,加强了海洋上混合层中的湍流垂向混合。为了研究海浪破碎对混合层中湍能量收支的影响,文中分析了海浪破碎对海洋上混合层中湍流生成的影响机制,采用垂向一维湍封闭混合模式,通过改变湍动能方程的上边界条件,引入了海浪破碎产生的湍动能通量,并分别对不同风速下海浪破碎的影响进行了数值研究,分析了混合层中湍能量收支的变化。当考虑海浪破碎影响时,近海表次层中的垂直扩散项和耗散项都有显著的增加,该次层中被耗散的湍动能占整个混合层中耗散的总的湍能量的92.0%,比无海浪破碎影响的结果增加了近1倍;由于平均流场切变减小,混合层中的湍流剪切生成减小了3.5%,形成一种存在于湍动能的耗散和垂直扩散之间的局部平衡关系。在该次层以下,局部平衡关系与壁层定律的结论一致,即湍动能的剪切生成与耗散相平衡。研究结果表明,海浪破碎在海表产生的湍动能通量影响了海洋上混合层中的各项湍能量收支间的局部平衡关系。     

Southern Ocean transformation in a coupled model with and without eddy mass fluxes

A coupled air–sea general circulation model is used to simulate the global circulation. Different parameterizations of lateral mixing in the ocean by eddies, horizontal, isopycnal, and isopycnal plus eddy advective flux, are compared from the perspective of water mass transformation in the Southern Ocean. The different mixing physics imply different buoyancy equilibria in the surface mixed layer, different transformations, and therefore a variety of meridional overturning streamfunctions. The coupled‐model approach avoids strong artificial water mass transformation associated with relaxation to prescribed mixed layer conditions. Instead, transformation results from the more physical non‐local, nonlinear interdependence of sea‐surface temperature, air–sea fluxes, and circulation in the model's atmosphere and ocean. The development of a stronger mid‐depth circulation cell and associated upwelling when eddy fluxes are present, is examined. The strength of overturning is diagnosed in density coordinates using the transformation framework.     

Evidence of change in the winter mixed layer in the Northeast Pacific Ocean

Sea-surface temperatures in the Northeast Pacific Ocean show a warming trend, and salinities show a declining trend, in data collected over the last 60 years. These changes combine to reduce the density of the surface layer over a large area of the Northeast Pacific. The declining surface density changes the energetic requirements for the formation of a surface mixed layer, and observations at Ocean Station Papa indicate that mid-winter mixed layer depths are showing a marked decline. The reduction in the depth of penetration of the winter-time mixed layer should reduce the nutrients entrained into the upper ocean each winter. Observations suggest that near surface nutrient levels are declining at Papa but remain well above levels that might inhibit productivity. However, at present the productivity of large phytoplankton appears to be limited by iron supply which is thought to be mainly from the atmosphere. A shallower mixed layer depth could increase the concentration of iron in this layer. The increase in iron would increase the utilization of nitrate, mainly by diatoms, and new production and the f ratio would increase.     

Effect of Stokes drift on upper ocean mixing

Stokes drift is the main source of vertical vorticity in the ocean mixed layer. In the ways of Coriolis - Stokes forcing and Langmuir circulations, Stokes drift can substantially affect the whole mixed layer. A modified Mellor-Yamada 2. 5 level turbulence closure model is used to parameterize its effect on upper ocean mixing conventionally. Results show that comparing surface heating with wave breaking, Stokes drift plays the most important role in the entire ocean mixed layer, especially in the subsurface layer. As expected, Stokes drift elevates both the dissipation rate and the turbulence energy in the upper ocean mixing. Also, ilffluence of the surface heating, wave breaking and wind speed on Stokes drift is investigated respectively. Research shows that it is significant and important to assessing the Stokes drift into ocean mixed layer studying. The laboratory observations are supporting numerical experiments quantitatively.     

东北季风与南海海洋环流的相互作用

针对冬、春季南海区风场，表层海流、海温场的季节变化，选用了２＾１／３层海洋模式和简单一层大气边界层模式，研究了冬、春季我作用下南海上层海洋环流的基本形态及其对ＳＳＴ的影响，估算了这种影响对海南风场的反馈效应。研究结果表明，冬、春季东北 与南海五流的相互作用对吕宋岛西部海域的气旋式冷涡的形成和维持有利。冬季（１月）强东北风作用使南海上层为一气旋式环流，上层环流对季风的反馈作用可使南海西北部东北风减弱     

简单海-气边界层模式中的埃克曼流动Ⅰ——无限深海的情形

近十余年来,海洋和大气相互作用这一课题日益受到人们的关注。从海-气边界层结构以及通过海面的物理量和化学量输送机制的研究到大尺度海洋和大气相互作用的研究都取得了可喜的成果。此外,还从海洋和大气相互作用的观点探索了风暴潮预报的新的可能途径[2]。然而,由于问题的复杂性,通过海面以及海-气边界层的物理量的小尺度输送机制迄未得到澄清,企图从本质上改善大尺度海洋和大气相互作用的理论是不现实的。     

表面波浪对海洋上层混合的作用

A new three-dimensional numerical model is derived through a wave average on the primitive N-S equations, in which both the＂Coriolis-Stokes forcing＂ and the＂Stokes-Vortex force＂ are considered. Three ideal experiments are run using the new model applied to the Princeton ocean model （POM）. Numerical results show that surface waves play an important role on the mixing of the upper ocean. The mixed layer is enhanced when wave effect is considered in conjunction with small Langmuir numbers. Both surface wave breaking and Stokes production can strengthen the turbulent mixing near the surface. However, the influence of wave breaking is limited to a thin layer, but Stokes drift can affect the whole mixed layer. Furthermore, the vertical mixing coefficients clearly rise in the mixed layer, and the upper ocean mixed layer is deepened especially in the Antarctic Circumpolar Current when the model is applied to global simulations. It indicates that the surface gravity waves are indispensable in enhancing the mixing in the upper ocean, and should be accounted for in ocean general circulation models.     

The seasonal cycle of submesoscale flows

The seasonal cycle of submesoscale flows in the upper ocean is investigated in an idealised model domain analogous to mid-latitude open ocean regions. Submesoscale processes become much stronger as the resolution is increased, though with limited evidence for convergence of the solutions. Frontogenetical processes increase horizontal buoyancy gradients when the mixed layer is shallow in summer, while overturning instabilities weaken the horizontal buoyancy gradients as the mixed layer deepens in winter. The horizontal wavenumber spectral slopes of surface temperature and velocity are steep in summer and then shallow in winter. This is consistent with stronger mixed layer instabilities developing as the mixed layer deepens and energising the submesoscale. The degree of geostrophic balance falls as the resolution is made finer, with evidence for stronger non-linear and high-frequency processes becoming more important as the mixed layer deepens. Ekman buoyancy fluxes can be much stronger than surface cooling and are locally dominant in setting the stratification and the potential vorticity at fronts, particularly in the early winter. Up to 30% of the mixed layer volume in winter has negative potential vorticity and symmetric instability is predicted inside mesoscale eddies as well as in the frontal regions outside of the vortices.     

A singular evolutive extended Kalman filter to assimilate ocean color data in a coupled physical–biochemical model of the North Atlantic ocean

Within the European DIADEM project, a data assimilation system for coupled ocean circulation and marine ecosystem models has been implemented for the North Atlantic and the Nordic Seas. One objective of this project is to demonstrate the relevance of sophisticated methods to assimilate satellite data such as altimetry, surface temperature and ocean color, into realistic ocean models. In this paper, the singular evolutive extended Kalman (SEEK) filter, which is an advanced assimilation scheme where three-dimensional, multivariate error statistics are taken into account, is used to assimilate ocean color data into the biological component of the coupled system. The marine ecosystem model, derived from the FDM model [J. Mar. Res. 48 (1990) 591], includes 11 nitrogen and carbon compartments and describes the synthesis of organic matter in the euphotic zone, its consumption by animals of upper trophic levels, and the recycling of detritic material in the deep ocean. The circulation model coupled to the ecosystem is the Miami isopycnic coordinate ocean model (MICOM), which covers the Atlantic and the Arctic Oceans with an enhanced resolution in the North Atlantic basin. The model is forced with realistic ECMWF ocean/atmosphere fluxes, which permits to resolve the seasonal variability of the circulation and mixed layer properties. In the twin assimimation experiments reported here, the predictions of the coupled model are corrected every 10 days using pseudo-measurements of surface phytoplankton as a substitute to chlorophyll concentrations measured from space. The diagnostics of these experiments indicate that the assimilation is feasible with a reduced-order Kalman filter of small rank (of order 10) as long as a sufficiently good identification of the error structure is available. In addition, the control of non-observed quantities such as zooplankton and nitrate concentrations is made possible, owing to the multivariate nature of the analysis scheme. However, a too severe truncation of the error sub-space downgrades the propagation of surface information below the mixed layer. The reduction of the actual state vector to the surface layers is therefore investigated to improve the estimation process in the perspective of sea-viewing wide field-of-view sensor (SeaWiFS) data assimilation experiments.