Sensitivity studies with the North Atlantic sigma coordinate Princeton Ocean Model

The sigma coordinate, Princeton Ocean Model (POM) has been configured for the North Atlantic Ocean between 5°N and 50°N as part of data assimilation, model predictability and intercomparison studies. The model uses a curvilinear orthogonal grid with higher resolution in the western North Atlantic and lower resolution in the eastern North Atlantic. A series of experiments, each one of a 10-year duration, are performed to evaluate the sensitivity of the ocean mean state and variability to model parameters and model configuration; these experiments include open vs. closed boundary conditions, low vs. high resolution grids, and different choices of diffusion and viscosity. The results show that the use of closed boundaries together with near-boundary buffer zones where temperature and salinity are relaxed towards the observed values give less realistic flows, weaker recirculation gyres and less realistic Gulf Stream separation than do open boundary conditions. The experiments show that the sensitivity of the ocean variability in the model to the choice of the Smagorinsky diffusion and viscosity coefficients significantly differs from one region to another and largely depends on other attributes such as the mean position of the Gulf Stream in each simulation. A 50% change in model resolution in the Gulf Stream region has a larger effect on ocean variability than a change of diffusivity by a factor of 10. In areas where either the high or the low resolution models have sufficient resolution, as in the Gulf of Mexico, they are able to produce variability comparable to that observed from altimeter data; elsewhere, model variability is underestimated.     

Hydrography and Circulation in the Eastern Tropical Indian Ocean during April-May 2011

The distribution of hydrography and circulation in the eastern tropical Indian Ocean(ETIO) during April-May 2011 were analyzed using cruise observations,satellite observations,and historic hydrographic data.It was observed that warm water(28℃) occupies the upper 50-m layer in the ETIO.Low-salinity surface water was observed at the mouth of the Bay of Bengal(BOB),which further extends to the Arabian Sea and off Sumatra via the Sri Lanka coast and the eastern bay mouth.Arabian Sea high-salinity water(ASHSW) is carried eastward along the equator to around 90°E by the equatorial undercurrent(EUC).It also runs south of Sri Lanka(north to 3°N) and in the western bay mouth(west to 87°E) but is much shallower than its counterpart at the equator.It is suggested to be the residual of the ASHSW,which intrudes into the BOB during the preceding southwest monsoon.Our results also show that,in the south of Sri Lanka,just below this subsurface high-salinity water,very-low-salinity water(about 34.8) occurs at depths of 100-200 m.Further analysis suggests that this low-salinity water comes from the BOB.     

冬季热带印度洋上层流场异常模态分析

利用复经验正交函数(CEOF)分解对冬季热带印度洋海洋上层流场异常做了模态分析和结果讨论,得到以下主要结果:该流场异常前两个模态均呈现赤道俘获波形式,其异常在赤道上最大,向南北两侧迅速衰减,呈现纬向流的形态;第一、二模态的性质分别是大洋赤道波动的半波和1波形态,这表明此时赤道波动异常在大洋流场异常中占有重要地位。冬季第一模态大洋垂直运动所导致的近表层海温异常与春、秋季不同,此时在赤道印度洋呈现正—负—正的经向分布态势,这与印度洋耦极子(Indian Ocean Dipole,IOD)的不同,并是IOD在冬季衰亡的直接原因。第二模态相应的海温异常则在赤道东印度洋呈现北负南正的分布态势。第一模态与南亚冬季风异常密切有关,为印度洋冬季风环流模态。第一、二模态都有明显的年际变化和年代际变化,年际变化均为3~5年,主要的年代际变化则分别为约18、22年,此外两者还均有约13年的年代际变化。本文第一、二模态年代际变化的主周期也是冬季北太平洋和冬季热带太平洋流场异常第二、一模态的主周期。     

中国南方夏季降水与热带印度洋偶极型海温异常的联系

利用1979-1999年GISST和CMAP月平均资料,用线性回归滤除印度洋偶极子(IOD)指数和ENSO的相互干扰,定义纯IOD指数和纯Nino3指数,将海温距平处理为相对独立的3个部分,通过相关和合成分析得到:6-8月印度洋偶极型海温及热带中印度洋海温异常与中国南方夏季降水都有很好的正相关关系,并且二者对南方夏季降水序列的拟合方差贡献显著,表明热带印度洋海温异常与中国南方夏季降水的关系密切;5月份热带印度洋海温年际变化可以解释60 %左右的南方夏季降水异常,这对南方降水的预测具有非常好的指导意义.在正(负)IOD年,热带印度洋SSTA引起我国南方地区大气异常上升(下沉)运动,中国南方为整层水汽的异常辐合(辐散)区,从而使中国南方夏季降水异常偏多(偏少).     

The Impact of the Tropical Indian Ocean on South Asian High in Boreal Summer

The tropical Indian Ocean (TIO) is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High (SAH) in summer. When the TIO is warmer, the SAH strengthens and its center shifts southward. It is found that the variations in the SAH cannot be accounted for by the precipitation anomaly. A possible mechanism is proposed to explain the connection between the TIO and SAH: warmer SST in the TIO changes the equivalent potential temperature (EPT) in the atmospheric boundary layer (ABL), alters the temperature profile of the moist atmosphere, warms the troposphere, which produces significant positive height anomaly over South Asia and modifies the SAH. An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skill in the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. The experiment with idealized heating over the TIO reproduced the response of the SAH to TIO warming. The results suggest that the TIO-induced EPT change in the ABL can account for the variations in the SAH.     

南半球对流层大气对热带太平洋-印度洋海温异常综合模的响应及其机制解释

利用NOAA SST及NCEP/NCAR再分析资料, 研究了热带太平洋—印度洋海温异常综合模和南半球对流层大气之间的遥相关模态并对其进行了机制解释。首先通过相关和合成分析, 给出了遥相关的空间模态, 结果表明: 北半球秋、冬季, 在南半球对流层大气存在和热带太平洋—印度洋海温异常综合模密切联系的遥相关作用中心, 该中心的分布构成一列明显的从赤道中太平洋出发, 最终到达非洲中南部及赤道印度洋的Rossby波列, 将赤道太平洋、印度洋与南半球中高纬度大气连接起来, 起到了类似“大气桥” 的作用。而单纯IOD和单纯ENSO均难以在南半球对流层激发出遥相关波列, 进一步证实了两者共同作用的影响。其次, 利用行星波能量传播理论对两者之间的遥相关进行了机制分析, 发现纬向波数为1～3的大气行星波的能量传播是热带太平洋—印度洋海温异常综合模与南半球对流层大气之间遥相关的一种可能的联系方式。     

Distribution of CO2 parameters in the Western Tropical Atlantic Ocean

The variability of sea surface Total Alkalinity (TA) and sea surface Total Inorganic Carbon (C_T) is examined using all available data in the western tropical Atlantic (WTA: 20°S-20°N, 60°W-20°W). Lowest TA and C_T are observed for the region located between 0°N-15°N/60°W-50°W and are explained by the influence of the Amazon plume during boreal summer. In the southern part of the area, 20°S-10°S/40°W-60°W, the highest values of TA and C_T are linked to the CO₂–rich waters due to the equatorial upwelling, which are transported by the South Equatorial Current (SEC) flowing from the African coast to the Brazilian shore. An increase of C_T of 0.9 ± 0.3 μmol kg⁻¹yr⁻¹ has been observed in the SEC region and is consistent with previous published estimates. A revised C_T-Sea Surface Salinity (SSS) relationship is proposed for the WTA to take into account the variability of C_T at low salinities. This new C_T-SSS relationship together with a published TA-SSS relationship allow to calculate pCO₂ values that compare well with observed pCO₂ (R² = 0.90).     

Circulation Patterns Linked to the Positive Sub-Tropical Indian Ocean Dipole

The positive phase of the subtropical Indian Ocean dipole(SIOD) is one of the climatic modes in the subtropical southern Indian Ocean that influences the austral summer inter-annual rainfall variability in parts of southern Africa. This paper examines austral summer rain-bearing circulation types(CTs) in Africa south of the equator that are related to the positive SIOD and the dynamics through which specific rainfall regions in southern Africa can be influenced by this relationship. Four austral...     

热带环流演变与南海季风爆发

利用1958－1997年的NCEP／NCAR再分析资料，分析了南、北半球中低纬环流的气候特征，并讨论了南海夏季风爆发与大尺度环流的关系。研究发现阿拉伯海经向环流管的上升气流和南半球纬向环流管的上升气流在5月份同时到达南海，经向环流管低层的偏西风和纬向环管低层的偏南风共同组成西南风，于是5月份西南季风在南海地区首先爆发。此外，由于青藏高原地形及各经度海陆分布的影响，造成太阳辐射加热不均，是热带夏季风爆发的直接原因，也是南海季风早于印度风爆发的重要原因。     

热带印度洋和太平洋增暖对东亚夏季风趋势的相反影响

利用多成员集合试验结果,比较分析了热带印度洋和太平洋增暖各自对东亚夏季风趋势变化的影响。试验所用模式是GFDLAM2大气环流模式,增暖是通过在气候平均海洋表面温度（SST）基础上,叠加随时间线性增加的、相当于实际50a左右达到的SST异常来实现的。结果表明：热带印度洋和太平洋共同增暖有使东亚夏季风减弱的趋势。相比较而言,单独印度洋增暖有使东亚夏季风增强、华北降水增多的趋势,而单独太平洋增暖有使东亚夏季风减弱的趋势,即印度洋增暖与太平洋增暖对东亚夏季风存在相反的、竞争性影响。进一步分析指出,热带太平洋特别是热带中东太平洋的增温可能对20世纪70年代末期开始的夏季风年代际减弱有更重要的贡献;在未来热带印度洋和太平洋持续增暖、但增暖强度纬向差异减小的新情况下,东亚夏季风减弱的趋势可能还将持续。     

The Tropical Pacific–Indian Ocean Associated Mode Simulated by LICOM2.0

Oceanic general circulation models have become an important tool for the study of marine status and change. This paper reports a numerical simulation carried out using LICOM2.0 and the forcing field from CORE. When compared with SODA reanalysis data and ERSST.v3 b data, the patterns and variability of the tropical Pacific–Indian Ocean associated mode(PIOAM) are reproduced very well in this experiment. This indicates that, when the tropical central–western Indian Ocean and central–eastern Pacific are abnormally warmer/colder, the tropical eastern Indian Ocean and western Pacific are correspondingly colder/warmer. This further confirms that the tropical PIOAM is an important mode that is not only significant in the SST anomaly field, but also more obviously in the subsurface ocean temperature anomaly field. The surface associated mode index(SAMI) and the thermocline(i.e., subsurface) associated mode index(TAMI) calculated using the model output data are both consistent with the values of these indices derived from observation and reanalysis data. However, the model SAMI and TAMI are more closely and synchronously related to each other.     

热带印度洋春季海表温度异常与南海夏季风强度变化的关系

利用50年的Reynolds月平均海表温度资料和NCEP/NCAR全球大气再分析资料,分析了热带印度洋春季海温异常对南海夏季风强度变化的影响。结果表明:1)热带印度洋春季海表温度距平(SSTA)的模态主要是全区一致型(USBM)和热带南印度洋偶极型(SIODM),USBM模态既有年际时间尺度的变化特征,又有年际以上时间尺度的变化特征,既包含有对冬季ENSO信号响应的变化特征,又有独立于ENSO的变化特征;SIODM模态主要表现为独立于ENSO的年际时间尺度变化。2)USBM模态与南海夏季风强度变化呈显著负相关关系,且二者都是对冬季ENSO信号的响应,USBM模态的年际变化不能独立于ENSO信号影响南海夏季风的强度变化。3)经(1~8年)带通滤波及去除ENSO信号的热带印度洋春季SSTA的SIODM型分布是影响南海夏季风强度变化的主要模态,表现为热带东南印度洋为负(正)、其他海区为正(负)时,南海夏季风强度增强(减弱),大气环流对热带东南印度洋SSTA热力作用的响应是造成这一关系的直接原因,SIODM型的SSTA分布与南海夏季风年际异常关系在热带印度洋长期变化趋势的暖位相期显著,在长期变化趋势的冷位相期不显著。     

Modulation of Madden-Julian Oscillation Activity by the Tropical Pacific-Indian Ocean Associated Mode

In this study, the impacts of the tropical Pacific–Indian Ocean associated mode(PIOAM) on Madden–Julian Oscillation(MJO) activity were investigated using reanalysis data. In the positive(negative) phase of the PIOAM, the amplitudes of MJO zonal wind and outgoing longwave radiation are significantly weakened(enhanced) over the Indian Ocean, while they are enhanced(weakened) over the central and eastern Pacific. The eastward propagation of the MJO can extend to the central Pacific in the positive ...     

热带太平洋-印度洋海温异常综合模对南亚高压的影响

从综合考虑热带太平洋和印度洋海温异常特征出发,研究了热带太平洋-印度洋海温异常综合模对南亚高压的影响.当热带太平洋-印度洋海温异常综合模为正位相(西印度洋和东太平洋海温距平为正,东印度洋-西太平洋海温距平为负),南亚高压偏弱,位置偏东偏南;当热带太平洋-印度洋海温异常综合模为负位相(西印度洋和东太平洋海温距平为负,东印度洋-西太平洋海温距平为正),南亚高压偏强,位置偏西偏北.热带太平洋-印度洋海温异常综合模影响南亚高压主要通过三种机制:一是通过影响亚洲季风从而影响了降水潜热形成的大气加热场分布,在正(负)位相年,青藏高原大气热源为负(正)异常,因此青藏高原上空空气上升减弱(加强),南亚高压偏弱(偏强);南海季风和热带辐合带加强(减弱),菲律宾附近的大气热源加强(减弱),有利于上空青藏高原东南侧反气旋(气旋)式的距平环流,因此南亚高压偏东偏南(偏西偏北).二是热带太平洋-印度洋海温的纬向热力对比引起赤道纬向垂直(Walker)环流异常,必将引起高空纬向风异常,在正(负)位相年,南亚高压南部的印度洋高空会出现西(东)风异常,导致南亚高压偏弱(偏强).三是综合模的正(负)异常加强(减小)西印度洋经度范围的区域Hadley环流,其北侧伊朗高原上的异常下沉(上升)支,造成南亚高压偏弱(偏强),位置偏东偏南(偏西偏北).     

Model evaluation experiments in the North Atlantic Basin: simulations in nonlinear terrain-following coordinates

A primitive equation ocean circulation model in nonlinear terrain-following coordinates is applied to a decadal-length simulation of the circulation in the North Atlantic Ocean. In addition to the stretched sigma coordinate, novel features of the model include the utilization of a weakly dissipative, third-order scheme for tracer advection, and a conservative and constancy-preserving time-stepping algorithm. The objectives of the study are to assess the quality of the new terrain-following model in the limit of realistic basin-scale simulations, and to compare the results obtained with it against those of other North Atlantic models used in recent multi-model comparison studies.The new model is able to reproduce many features of both the wind-driven and thermohaline circulation, and to do so within error bounds comparable with prior model simulations (e.g., CME and DYNAMO). Quantitative comparison with comparable results obtained with the Miami Isopycnic Coordinate Model (MICOM) show our terrain-following solutions are of similar overall quality when viewed against known measures of merit including meridional overturning and heat flux, Florida Straits and Gulf Stream transport, seasonal cycling of temperature and salinity, and upper ocean currents and tracer fields in the eastern North Atlantic Basin. Sensitivity studies confirm that the nonlinear vertical coordinate contributes significantly to model fidelity, and that the global inventories and spatial structure of the tracer fields are affected in important ways by the choice of lateral advection scheme.     

热带大气平均环流的纬向不均匀性和Kelvin波的动力作用

本文利用一个包含Wave-CISK机制以及蒸发、感热与扰动风场的反馈机制，并引入实际的下垫面温度分布和海陆差异的热带大气模式，较好地模拟了低纬平均环流在风场、散度场及低层位势高度场上的纬向非均匀性。分析表明这种纬向非对称性是由于下垫面的热力非均匀性造成的强迫与大气内部的热力-动力反馈过程相互作用的结果。对热力强迫的响应形成了西太平洋暖水区上的西风和东太平洋上的东风，而对简化模式的解析分析说明，由于热力-动力反馈造成的Kelvin波的发展过程，可以解释平均东风强于西风的事实。     

7—9月登陆华南热带气旋频数异常与大气环流和海温的关系

利用1949—2021年中国气象局上海台风研究所热带气旋资料、NCEP/NCAR再分析资料、NOAA重构的海表温度资料（SST）和大气向外长波辐射（OLR）资料,采用线性趋势分析、Mann-Kendall检验等方法分析了近73年7—9月登陆华南热带气旋频数的变化特征。采用合成分析的方法研究7—9月登陆华南热带气旋频数异常与同期大气环流和海温的关系。结果表明,1949—2021年7—9月,登陆华南热带气旋有243个,年均3.3个,占全年登陆总数的70.2%。登陆华南热带气旋频数具有显著的年际和年代际变化特征。1973年最多（7个）,1950年最少（0个）;在1990年代中期由前期偏多转为后期偏少,但没有突变发生。近73年7—9月登陆华南热带气旋频数以0.1（10a）-1的速率减少。7—9月登陆华南热带气旋频数异常与大气环流和海温异常密切相关,在异常多、少年同期：（1）大气环流差值场上,南亚高压偏强、偏东、偏北,副高偏西、偏北、偏强,110°E以东的赤道东风引导气流偏强,季风槽加强,北半球中低纬海平面气压场东高西低,北高南低,同时南海、热带西太平洋对流活动加强。（2）海温差值场上,赤道中东太平洋偏冷,西太平洋暖池偏暖,沃克环流加强。高中低层大气环流和海温这种差异可能是导致登陆华南热带气旋频数异常的原因。     

一个大洋环流模式和相应的海气耦合模式的评估 I.热带太平洋年平均状态

评估了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海洋环流模式L30T63和海气耦合模式FGCM 0模拟的热带太平洋年平均状态 ,资料取自L30T63由观测的大气强迫驱动的Control试验、由NCARCCM3大气强迫驱动的Spinup试验、以及相应的海气耦合模式FGCM 0。主要的结论是 :( 1 )在“准确”的海表强迫下 ,Control模拟的海面温度和温跃层与观测结果相当接近 ,模式的固有误差是赤道冷舌过分西伸和东南太平洋温跃层偏浅。 ( 2 )Spinup能模拟出合理的热带太平洋上层海洋环流 ,但存在两个问题 ,即 :暖池区海面温度显著偏高、沿赤道的梯度过大 ;赤道温跃层偏浅、东西向坡度偏小 ,它们分别与CCM3提供的海表短波辐射通量和风应力的系统误差有关。这两个问题很可能是海气耦合模式FGCM 0运行初期误差迅速发展的重要原因。 ( 3)FGCM 0模拟的赤道暖池区上层 1 0 0m的平均温度比观测低 3℃。分析表明FGCM 0夸大了暖池区海洋动力过程的降温作用 ,使得模拟的“暖池”在一定程度上具有冷舌的属性。FGCM 0模拟的热带南太平洋温跃层比观测结果偏浅数十米到 1 0 0m ,以致赤道两侧的上层海洋温度分布趋于对称 ,成为“doubleITCZ”现象在上层海洋中的表现。风应力旋度的系统误差和垂直混合随深度衰减过快     

The Relationship Between Indian Ocean SST and Tropical Cyclone Genesis Frequency over North Indian Ocean in May

Tropical cyclone (TC) activities in the North Indian Ocean (NIO) peak in May during the pre-monsoon period, but the TC frequency shows obvious inter-annual variations. By conducting statistical analysis and dynamic diagnosis of long-term data from 1948 to 2016, the relationship between the inter-annual variations of Indian Ocean SST and NIO TC genesis frequency in May is analyzed in this paper. Furthermore, the potential mechanism concerning the effect of SST anomaly on TC frequency is also investigated. The findings are as follows: 1) there is a broadly consistent negative correlation between NIO TC frequency in May and SST in the Indian Ocean from March to May, with the key influencing area located in the southwestern Indian Ocean (SWIO); 2) the anomalies of SST in SWIO (SWIO-SST) are closely related to a teleconnection pattern surrounding the Indian Ocean, which can significantly modulate the high-level divergence, mid-level vertical motion and other related environmental factors and ultimately influence the formation of TCs over the NIO; 3) the increasing trend of SWIO-SST may play an essential role in the downward trend of NIO TC frequency over the past 69 years.     

印度洋海气相互作用对热带夏季大气环流气候态的影响

利用分辨率较高的SINTEX-F(Scale INTeraction EXperiment-FRCGC) 海气耦合模式, 进行多组长时间积分模拟和理想试验, 分析研究热带印度洋海气耦合对夏季大气环流气候态的影响。主要结果有: (1) 热带印度洋海气相互作用使热带东印度洋产生明显的东风变化, 使热带中西太平洋赤道北部产生气旋性切变变化。 (2) 印度洋海气相互作用对大气环流气候态的影响绝大部分由于大气对海气相互作用的响应存在年际变化正负距平不对称性造成, 这种年际变化不对称性包括正偶极子与负偶极子的不对称、 海盆宽度正异常与海盆宽度负异常的不对称。 (3) 年际和季节内两种时间尺度海气相互作用对印度洋关键区大气环流平均态都有影响, 约各占60%、 40%; 季节内尺度海气相互作用对太平洋近赤道区大气环流平均态有重要影响; 年际尺度海气相互作用对太平洋赤道外地区大气环流平均态有重要影响。热带印度洋年际尺度、 季节内尺度海气相互作用对大气环流气候态的影响, 都存在年际变化以及年际变化正负距平不对称性。这两种尺度海气相互作用主要通过年际变化正负距平不对称性而对大气环流平均态产生影响。