A THEORETICAL SOLUTION FOR THE THERMOHALINE CIRCULATION IN THE SOUTHERN YELLOW SEA

Application of the thermocline equations in the thermocline areas and the boundary layer and the asymptotic matching techniques in each boundary in order to satisfy the surface and bottom conditions yielded a theoretical 2- D solution of the vertical thermohaline circulation of the Southern Yellow Sea in summer when the quasi-statically varying seasonal thermocline (density layer) is the background density structure , the deviations from which cause the secondary vertical circulation . The results show that the thermocline can be considered as an internal boundary or a barrier to the vertical heat advection so that in the central areas of the Southern Yellow Sea or the center of the Yellow Sea Cold Water Mass(YCWM)】 the downwelling in the upper layer and upwelling in the lower or bottom layer form a double cell vertical circulation . The solution is similar to Hu’s conceptual model ( 1986) in the central areas of the YCWM and is consistent with observed temperature . salinity and dissolved oxygen

Response of the Asian Summer Monsoon to Weakening of Atlantic Thermohaline Circulation

Various paleoclimate records have shown that the Asian monsoon was punctuated by numerous suborbital time-scale events, and these events were coeval with those that happened in the North Atlantic. This study investigates the Asian summer monsoon responses to the Atlantic Ocean forcing by applying an additional freshwater flux into the North Atlantic. The simulated results indicate that the cold North Atlantic and warm South Atlantic induced by the weakened Atlantic thermohaline circulation （THC） due to the freshwater flux lead to significantly suppressed Asian summer monsoon. The authors analyzed the detailed processes of the Atlantic Ocean forcing on the Asian summer monsoon, and found that the atmospheric teleconnection in the eastern and central North Pacific and the atmosphere-ocean interaction in the tropical North Pacific play the most crucial role. Enhanced precipitation in the subtropical North Pacific extends the effects of Atlantic Ocean forcing from the eastern Pacific into the western Pacific, and the atmosphere-ocean interaction in the tropical Pacific and Indian Ocean intensifies the circulation and precipitation anomalies in the Pacific and East Asia.

Abrupt Climate Change around 4 ka BP:Role of the Thermohaline Circulation as Indicated by a GCM Experiment

A great deal of palaeoenvironmental and palaeoclimatic evidence suggests that a predominant temperature drop and an aridiflcation occurred at ca. 4.0 ka BP. Palaeoclimate studies in China support this dedution. The collapse of ancient civilizations at ca. 4.0 ka BP in the Nile Valley and Mesopotamia has been attributed to climate-induced aridification. A widespread alternation of the ancient cultures was also found in China at ca. 4.0 ka BP in concert with the collapse of the civilizations in the Old World. Palaeoclimatic studies indicate that the abrupt climate change at 4.0 ka BP is one of the realizations of the cold phase in millennial scale climate oscillations, which may be related to the modulation of the Thermohaline Circulation (THC) over the Atlantic Ocean. Therefore, this study conducts a numerical experiment of a GCM with SST forcing to simulate the impact of the weakening of the THC. Results show a drop in temperature from North Europe, the northern middle East Asia, and northern East Asia and a significant reduction of precipitation in East Africa, the Middle East, the Indian Peninsula, and the Yellow River Valley. This seems to support the idea that coldness and aridification at ca. 4.0 ka BP was caused by the weakening of the THC.

Simulation of Seasonal Circulations and Thermohaline Variabilities in the Gulf of Thailand

Based on the Princeton Ocean Model （POM）, the seasonal thermohaline feature and the ocean circulation in the Gulf of Thailand （GOT）, situated between 6°N to 14°N latitude and 99°E to 105°E longitude, were studied numerically with 37 × 97 orthogonal curvilinear grid and 10 vertical sigma levels conforming to a realistic bottom topography. A spin-up phase of the first model run was executed using wind stress calculated from climatological monthly mean wind, restoring-type surface heat and salt, and climatological monthly mean fresh water flux data. In this paper, the temperature and salinity fields taken from Levitus94 data sets and the calculated temperature and salinity from the model run for 12-month mean and for each season are presented where the winter, summer, rainy, and end of the rainy seasons of Thailand are represented by the months January, April, July, and October, respectively. The simulated circulations are also described. The results show that the temperature in the GoT is warmer than the temperature of the other parts connected to the South China Sea （SCS）. At any depth of inflow from SCS into the GoT, the salinity is high, but in the outflow from the GoT at the surface, the salinity is low. The strong circulations are clockwise during summer and the rainy seasons of Thailand, which are the East Asian monsoon periods, northeasterly and southwesterly during summer. They occur near Pattani and Narathiwat provinces during summer and in the central GoT during the rainy seasons. Sensitivity experiments were designed to investigate the effects of wind forcing and open boundary conditions. Wind forcing is shown to be the important factor for generating the circulation in the GoT. The lateral velocity at the open boundaries is of considerable importance to current circulation for the rainy and end of the rainy seasons, with insignificant effect for the winter and summer seasons of Thailand.

A Three-Box Model of Thermohaline Circulation under the Energy Constraint

The driving mechanism of thermohaline circulation is still a controversial topic in physical oceanography.Classic theory is based on Stommel's two-box model under buoyancy constraint.Recently,Guan and Huang proposed a new viewpoint in the framework of energy constraint with a two-box model.We extend it to a three-box model,including the effect of wind-driven circulation.Using this simple model,we further study how ocean mixing impacts on thermohaline circulation under the energy constraint.

Optimal nonlinear excitation of decadal variability of the North Atlantic thermohaline circulation

Nonlinear development of salinity perturbations in the Atlantic thermohaline circulation(THC) is investigated with a three-dimensional ocean circulation model,using the conditional nonlinear optimal perturbation method.The results show two types of optimal initial perturbations of sea surface salinity,one associated with freshwater and the other with salinity.Both types of perturbations excite decadal variability of the THC.Under the same amplitude of initial perturbation,the decadal variation induced by the freshwater perturbation is much stronger than that by the salinity perturbation,suggesting that the THC is more sensitive to freshwater than salinity perturbation.As the amplitude of initial perturbation increases,the decadal variations become stronger for both perturbations.For salinity perturbations,recovery time of the THC to return to steady state gradually saturates with increasing amplitude,whereas this recovery time increases remarkably for freshwater perturbations.A nonlinear(advective) feedback between density and velocity anomalies is proposed to explain these characteristics of decadal variability excitation.The results are consistent with previous ones from simple box models,and highlight the importance of nonlinear feedback in decadal THC variability.

Three-Dimensional Structure of Optimal Nonlinear Excitation for Decadal Variability of the Thermohaline Circulation

The decadal variability of the North Atlantic thermohaline circulation(THC) is investigated within a three-dimensional ocean circulation model using the conditional nonlinear optimal perturbation method. The results show that the optimal initial perturbations of temperature and salinity exciting the strongest decadal THC variations have similar structures: the perturbations are mainly in the northwestern basin at a depth ranging from 1500 to 3000 m. These temperature and salinity perturbations act as the optimal precursors for future modifications of the THC, highlighting the importance of observations in the northwestern basin to monitor the variations of temperature and salinity at depth. The decadal THC variation in the nonlinear model initialized by the optimal salinity perturbations is much stronger than that caused by the optimal temperature perturbations, indicating that salinity variations might play a relatively important role in exciting the decadal THC variability. Moreover, the decadal THC variations in the tangent linear and nonlinear models show remarkably different characteristics, suggesting the importance of nonlinear processes in the decadal variability of the THC.

Changes in Atlantic Thermohaline Circulation under Different Atmospheric CO_2 Scenarios in a Climate Model

The changes in the thermohaline circulation （THC） because of the increased CO2 in the atmosphere play an important role in future climate regimes. In this article, a new climate model developed at the Max-Planck Institute for Meteorology is used to study the variation in THC strength, the changes of North Atlantic deep-water （NADW） formation, and the regional responses of the THC in the North Atlantic to increasing atmospheric CO2. From 2000 to 2100, under increased CO2 scenarios （B1, AIB, and A2）, the strength of THC decreases by 4 Sv （106 m^3/s）, 5.1 Sv, and 5.2 Sv, respectively, equivalent to a reduction of 20%, 25%, and 25.1% of the present THC strength. The analyses show that the oceanic deep convective activity significantly strengthens in the Greenland-leeland-Norway （GIN） Seas owing to saltier （denser） upper oceans, whereas weakens in the Labrador Sea and in the south of the Denmark Strait region （SDSR） because of surface warming and freshening due to global warming. The saltiness of the GIN Seas is mainly caused by the increase of the saline North Atlantic inflow through the Faro-Bank （FB） Channel. Under the scenario A1B, the deep-water formation rate in the North Atlantic decreases from 16.2 Sv to 12.9 Sv with increasing CO2.

Glacial Thermohaline Circulation and Climate:Forcing from the North or South?

Based on the evidence available from both observations and model simulations, the author proposes a view that may provide a unified interpretation of the North Atlantic thermohaline variability. Because of the slow response time of the Southern Ocean （millennia） and the relatively faster response time of the North Atlantic （centuries）, the North Atlantic thermohaline circulation is controlled predominantly by the climate forcing over the Southern Ocean at the long glacial cycle timescales, but by the North Atlantic climate forcing at the short millennial timescaies.

The South China Sea thermohaline structure and circulation

In this study, we used the Navy' s Master Oceanographic Observation Data Set(MOODS), consisting of 116019 temperature and 9617 salinity profiles, during 1968-1984 to investigate the temporal and spatial variabilities of South China Sea thermohaline structures and circulation. For temperature, profiles were binned into 204 monthly data sets from 1968 to 1984 (17 years). For salinity, profiles were binned into 12 climatological monthly data sets due to the data paucity. A two-scale optimal interpolation method was used to establish a three-dimensional monthly-varying gridded data set from MOODS, covering the area of 5°-25°N and 105° - 125°E and the depth from the surface to 400 m. After the gridded data set had been established, both composite analysis and the Empirical Orthogonal Function (EOF) analysis (for temperature only) were used to identify the major thermohaline fratures including annual mean, monthly anomalies, and interannual thermal variabilities. The inverted monthly circulation pattern using the P - vector method is also discussed.

冰在淡水还是盐水中熔化得更快?

冰在淡水还是盐水中熔化得更快,可以与温盐环流的驱动机理、新仙女木期全球变冷的成因猜测结合,形成一个物理学科主导的跨学科研究性学习项目.主要以师生对话的形式,介绍课题实施过程,说明每个环节的设计要点,供相关学校和教师参考使用.

全球气候变化下海洋环流多尺度演变:联动协同与环境生态效应初探

海洋环流是海洋系统物质能量收支、配置、平衡、维持和变化的关键通道与机制。从全球海洋视角,基于目前海洋环流多变率动力过程与趋势演变的认知,重点综述气候变化下海洋环流的海盆尺度三维联动特征机制、洋际交换与协同、世界大洋经向输运变化以及相关的海洋气候与环境生态效应,依据研究现状和需求,提出研究建议。结果表明:全球一致性变暖路径与进程调控下,受驱动因子的演变与胁迫,海洋环流变化对副热带中高纬地区年际、年代际气候与环境变迁具有突出作用影响,并可产生显著环境生态效应和严重致灾风险。建议加大专精特新观测仪器自主研发,通过国际合作加大中高纬海洋环流多尺度动力过程综合调查的参与度和主导性,增强多学科融合交叉研究力度,有效提升深层次海洋环流变异及动力、环境、生态灾害影响的气候变化综合风险预测预评估和防治能力,为海洋领域能源开发、生态系统保护、气候变化应对与灾害风险治理提供必要的动力学参考。

温室气体浓度增加情景下大西洋温盐环流的演变

温室气体浓度增加(以CO2为主)引起的温盐环流演变在未来气候系统中扮演非常重要的角色.在最新的温室气体排放情景下,利用基于德国马普气象研究所为IPCC第四次评估报告而最新发展的气候模式(ECHAM5/MPIOM),对3种不同的温室气体排放假设(B1,A1B,A2)进行了可靠的数值模拟.在此基础上,就大西洋温盐环流和北大西洋深层水形成的变化,以及北大西洋不同海区的温盐环流对温室气体浓度增加的响应,对模拟结果进行了分析.研究揭示,到21世纪末,在3种CO2排放情景下,温盐环流强度分别减弱了4Sv(1Sv=106m3/s)、5.1Sv、5.2Sv,大体相当于减弱了20%、25%、25.1%.由于全球变暖引起副极地海区表层海水变暖变淡,拉不拉多海(LabradorSea)和丹麦海峡(DenmarkStrait)以南区域的深层对流有所减弱.而在格陵兰-冰岛-挪威海(GINSea)的情况相反,由于北大西洋暖流的增强,通过法鲁海峡(Faro-BankChannel)进入GIN海域的高盐水增加,导致GIN海域上层盐度(密度)增加,进而深层对流加强.在A1B情景下,由于全球变暖北大西洋的深层水生成率从16.2Sv降到了12.9Sv.

海洋环流模式的发展和应用 Ⅰ.全球海洋环流模式

概述近10年来中国科学院大气物理研究所大气科学和地球流体动力学数值模拟国家重点实验室全球海洋环流模式的发展及其在全球海气耦合模式的发展和气候模拟方面的应用。重点是:一个30层、0.5°×0.5°的准全球海洋环流模式LICOM的建立及其模拟的热带太平洋海洋环流和印度尼西亚贯穿流;以20层海洋模式为海洋分量建立的全球海洋—大气—陆面系统耦合模式GOALS在气候变化模拟方面的应用,和以海洋模式L30T63为海洋分量建立的灵活的耦合环流模式FGCM-0在热带太平洋—印度洋海气相互作用及古海洋—古气候模拟方面的应用。

温盐环流稳定性以及年代际变率的研究进展

对近期国内外有关温盐环流的模拟研究作了综合评述,着重介绍温盐环流的稳定性、多平衡态及其转化以及年代际变率问题的研究进展。

大洋温盐环流与气候变率的关系研究:科学界的一个新课题

大洋温盐环流与气候变率的关系研究是 90年代中后期以来国际科学界提出的一个新课题。在概述温盐环流基本图像的基础上 ,讨论了温盐环流在气候系统中的重要作用 ,介绍了国际科学界针对该问题的未来行动 ,总结了国际科学界的研究现状。

孟加拉湾深海记录中的等深流活动特征及其环境意义初探

实地观测和对沉积记录的研究表明 ,孟加拉湾存在强大的等深流活动 .通过采自孟加拉深海扇东部和中部的 3支活塞岩心的沉积学研究表明 ,那些氧化色彩强烈、钙质生物壳体溶蚀严重、不存在粒序层理的粉砂质薄层实际上是等深积作用的产物 .源自两极的等深流是全球温盐循环系统的关键组分 ,它们在过去 15 0ka的历史中曾经多次得到强化 ,不仅对研究区的环境变化产生重要影响 ,而且可能作为纽带 ,加强了低纬地区与极区在气候意义上的遥相关 .等深流的强化与冰川旋回之间似乎不存在密切关联 ,氧同位素第 3 ,4,5期内均可发现明显的强化记录 .关于强化的控制机制有待深入探讨 .

大洋温盐环流的稳定性及变率模拟研究进展

围绕大洋温盐环流的稳定性和变率，以三维原始方程大洋环流模式（ＯＧＣＭ）和海气耦合模式为重点，兼顾理想概念模式，总结了近年来模拟研究的主要成果。概括了几个主要前沿方向———大洋温盐环流的多平衡态现象、数十年／年代际变率以及百年到千年尺度的变率特性等的研究成果，探讨了其内部机制。

一个太平洋海盆尺度环流模式及其模拟结果

在中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG)发展的全球气候海洋环流模式(LICOM)的基础上构建了一个太平洋海盆环流模式,并对其模拟结果进行了深入的分析。在模拟中对中尺度示踪物输送采用了两种方案,即传统的水平扩散方案(HOR)和包括涡旋诱导速度的等密度面扩散方案(GM)。对这两个试验的气候平衡态结果分析发现,该模式较好地模拟出了太平洋的环流特征,包括副热带大涡、副极地涡旋以及南极绕流(ACC)等。赤道附近的各种流系亦得到了较好的模拟,模拟的150°W赤道潜流的最大流速为40 cm/s,出现在次表层130 m左右,虽然模拟值比基于NCEP资料估计的最大流速80 cm/s小,但与其位置十分相近。两个试验均较好地模拟出了温盐的分布结构,包括北太平洋和南太平洋中层水的形成以及南极底层水的输送等。通过详细分析两个试验结果发现,总的说来在目前模式所采用的参数条件下,GM的结果稍好于HOR的结果。这些模拟结果表明,在LICOM基础上构建的太平洋环流模式从总体上是能再现许多观测特征的,可为今后进一步研究被动示踪物在北太平洋的分布等问题提供一个十分有用的工具。

全球热带气旋活动与全球气候变化相关特征

阐述全球气候变化对全球热带气旋活动的影响在国际上取得的进展。从3方面进行综合分析:(1)气候变化特征对全球热带气旋的影响;(2)热带气旋活动的年际变化和年代际振荡以及影响因子;(3)热带气旋活动与全球气候变化方面的数值模拟进展。总结国际上在这一领域取得的研究进展,全球气候变化主要以全球大气环流、海气相互作用、全球海面温度以及温盐环流(ThermohalineCirculation)这4个方面相互影响及其共同作用,可对全球热带气旋活动的发生频率、强度、路径趋势和登陆地区产生影响。