热带太平洋海洋混合层水体振荡与ENSO循环

研究了热带太平洋温跃层和海面风应力年际变率主要模态及它们之间的相互作用, 探讨了ENSO循环的可能形成机制, 得到如下结果: (1)热带太平洋温跃层异常具以160°W为纵轴的东西向偶极子分布和以6~8°N为横轴的南北向跷跷板分布等两种主要模态, 两者(相位差90°)组合构成El Niño/La Niña循环, 表现为混合层水体(指温跃层界面之上海温垂直分布较均匀的上层海洋)在赤道与12°N之间的热带太平洋海盆内反时针三维振荡; (2)热带太平洋风应力异常具两种主要分布型, 第一特征向量场反映了热带太平洋信风异常导致的赤道太平洋异常纬向风应力及散度场与离赤道北太平洋异常越赤道风应力及反相散度场, 第二特征向量场反映了热带辐合带(ITCZ)异常导致的异常风应力及相应散度场; (3)信风异常对ENSO事件的形成、强度和相变都有决定性的作用, 它导致海面倾斜, 提供了混合层水体振荡初始位能, 同时造成赤道太平洋西部与东部之间和赤道太平洋与12°N北太平洋海盆之间温跃层同步反相位移, 限定了热带太平洋混合层水体振荡的振幅和路线. ITCZ异常主要对ENSO相变过程有一定影响; (4)热带西太平洋海洋热力异常导致海面风应力异常, 它伴随热带太平洋混合层水体振荡沿赤道由西向东扩展, 造成热带太平洋信风异常, 产生有利于水体振荡的异常风应力及散度场, 反过来进一步加强混合层水体振荡. 这一海气耦合过程与混合层水体振荡一起为ENSO循环提供了相变和年际记忆机制. 研究指出, ENSO循环实质上是由信风异常和海气耦合过程共同作用下产生的热带太平洋海洋混合层水体在赤道与12°N之间热带太平洋海盆内的惯性振荡. 海气耦合过程产生的作用力大于或等于水体运动阻力时, ENSO循环将加强或维持, 不足以克服水体运动阻力时, 水体振荡减小, ENSO循环将逐渐减弱, 直至中断.     

厄尔尼诺/南方涛动与赤道远西太平洋准两年周期振荡之间相互作用的概念模式

建立了一个反映厄尔尼诺/南方涛动(ENSO)与热带远西太平洋准两年振荡(QBOWP)相互作用最基本物理过程的新概念模式. 在此概念模式中, QBOWP对ENSO的影响通过两种途径: (1) 沿赤道太平洋海洋Kelvin波和 (2) 大气的Walker环流; 而ENSO对QBOWP的影响则可通过大气的Walker环流异常来实现. 对该模式结果的分析诊断表明: 在ENSO与QBOWP相互作用过程中, 大气桥(Walker环流)的作用比海洋桥(沿赤道太平洋的Kelvin波)更重要; 通过QBOWP与ENSO的相互作用, 一个3~5年周期的ENSO振荡可以变为准两年振荡, 而赤道远西太平洋年际变化的主要周期也会变长; 热带太平洋大气-海洋耦合系统的多时间尺度的年际变化可以通过ENSO与QBOWP的相互作用来实现.     

地气角动量交换与ENSO循环

用1976～1989年的地球自转速度、赤道东太平洋海温和气压及大气角动量资料,研究了地气之间角动量交换与ENSO循环的关系结果表明:固体地球自转速度、赤道东太平洋海温、不同纬带及全球大气角动量之间存在着协同的变化关系;低纬局地海气相互作用通过Hadley环流可形成类似ENSO事件的循环;固体地球和全球海气相互作用通过山脉力矩和地转变速摩擦力矩形成了固体地球-海洋-大气系统中各个方面出现的非周期行为和非同步振荡;实际出现的ENSO循环是固海气相互作用反映在太平洋洋盆上的一种现象.     

北太平洋副热带高压年际变异与ENSO 循环之间的选择性相互作用

利用NCEP/NCAR大气再分析资料以及Hadley中心海表温度资料,针对北太平洋副热带高压(简称副高)的完整系统,通过分析超前于ENSO事件的海平面副高年际异常特征及其对ENSO事件的触发作用以及ENSO事件对500 hPa副高和海平面副高的滞后影响,结果表明了北太平洋副热带高压年际变异和ENSO循环之间存在选择性相互作用.即在大多数情况下,一方面,前期海平面副高减弱会导致热带西太平洋表面西风异常,通过海洋平流过程触发El Nino事件在夏季发生发展,在秋冬季成熟; 而另一方面,El Nino事件在秋冬季发展成熟后,增强了赤道中太平洋的对流性热源,通过对异常热源的动力响应,同期和次年夏季500 hPa副高增强,又通过增强的Hadley环流作用,副热带地区下沉运动增强,从而使得次年夏季海平面副高增强,增强的海平面副高又有利于触发下一个La Nina事件.副高年际变异和ENSO循环之间相互作用的选择性主要取决于副高异常是否接近于赤道以及ENSO事件本身的持续性.这种相互作用有利于在热带太平洋海气系统产生准两年振荡.     

风应力桥梁作用下热带太平洋和热带大西洋相互作用的数值试验

利用中等复杂程度热带大气和海洋模式研究了热带太平洋和大西洋SST通过风应力桥梁的相互作用.利用1958～1998年NCEP分析的海表面温度场（SST）强迫大气模式得到的表面风应力与NCEP分析的同期热通量共同驱动海洋模式,作为控制试验;和控制试验平行,但强迫大气模式的SST在某一海盆取为多年气候平均值的试验作为敏感性试验;比较控制试验与敏感性试验模拟,则可反映风应力桥梁作用下热带某海盆SST异常对其他海盆的影响.结果表明,热带某一海盆SST暖（冷）异常总是引起局地海盆表面西部西（东）风异常和东部东（西）风异常;热带太平洋SST暖（冷）异常导致的该海盆东部表面东（西）风异常可以扩展到热带大西洋,从而导致热带大西洋SST冷（暖）异常;热带大西洋SST暖（冷）异常导致的该海盆西部表面西（东）风异常可以扩展到热带太平洋,从而导致热带太平洋SST暖（冷）异常.     

LASG耦合气候系统模式FGCM-1.0

本文描述了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)最新发展的一个耦合气候系统模式的基本性能. 该模式是在LASG灵活的全球耦合气候系统模式（英文缩写为FGCM）的初始版本FGCM-0的基础上发展而来的,是该系列耦合模式的第二个版本,即FGCM-1.0. FGCM-1.0通过一个通量耦合器将大气、海洋和海冰三个分量模式耦合在一起,其中海洋分量模式是LASG发展的一个涡相容分辨率（eddy-permitting）全球海洋环流模式,大气和海冰分量模式则为美国国家大气研究中心（NCAR）的大气环流模式CAM2和海冰模式CSIM4. 耦合模式完整地考虑了海气界面上的动量、热量和淡水通量交换,尽管在模式中没有使用任何形式的人为的通量调整或者通量距平方案,模式还是比较合理地模拟出基本的气候形态. 通过对该耦合模式长期积分结果的进一步分析发现,模式能够比较好地模拟出厄尔尼诺－南方涛动（ENSO）以及印度洋偶极子事件的基本特征;与FGCM系列耦合模式的最初版本FGCM-0相比,FGCM-1.0模拟的北赤道逆流（NECC）和ENSO循环更加真实.     

亚洲和北美干湿变化及其与海表温度异常的关系

利用多通道奇异谱方法（MSSA）分析了1953~2003年亚洲和北美Palmer干旱指数（PDSI）与热带和北半球温带海洋海表面温度异常（SSTA）的主要周期振荡特征及其相互联系.结果表明：亚洲和北美PDSI以及SSTA均存在明显的3~6年的年际以及10年左右的年代尺度振荡;此外,亚洲PDSI还存在显著的6~8年的年际振荡.SSTA的年际振荡主要体现了ENSO的变化特征,而其年代尺度振荡的空间分布具有热带太平洋和北太平洋共同作用的类ENSO型.同时,MSSA的分析结果给出了亚洲和北美主要振荡信号的时间和空间演变特征.相关性分析表明,亚洲和北美PDSI的年际及年代尺度振荡均显示明显的对SSTA强迫信号的响应.对于年际振荡,亚洲PDSI对SSTA响应强于北美,但年代尺度振荡则反之.此外,亚洲和北美PDSI对于SSTA信号响应的关键区域也随时间尺度的不同而发生变化.亚洲的西西伯利亚、青藏高原东西两侧以及中西伯利亚东部在年际和年代尺度上均为受SSTA影响最显著的区域;在年际尺度上,北美中部地区的干湿变化与SSTA存在显著相关,而在年代尺度上,美国西部更易受SSTA年代尺度振荡的影响.     

FGOALS－g快速耦合模式模拟的北太平洋年代际变率

本文分析了由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/IAP）最新发展的FGOALS_－g快速耦合模式300 a积分模拟结果,通过与多种观测资料的对比分析,讨论了北太平洋年代际变率的时空结构、主要年代际模态的演变特征以及与ENSO的联系等研究内容. 结果表明：该模式能成功模拟出北太平洋年代际变率的主要空间分布特征;模拟的年代际模态具有多时间尺度性,其中最显著的是周期约为10～20 a左右的准20年振荡模态,该模态上层海洋热容量异常的演变过程主要表现为大致沿副热带海洋涡旋做海盆尺度顺时针旋转的特征,相应的大气异常不仅与阿留申低压的变异有关,而且与太平洋-北美PNA）遥相关型以及上游的欧亚大气环流异常有密切关系;模拟的北太平洋年代际变率对年际ENSO循环的发生频率和强度有明显的调制作用. 但模拟的KOE区和阿拉斯加湾SST异常振幅比观测偏强,这与模式海冰偏多、高纬度SST偏冷的误差有关.     

热带西太平洋和南印度洋近20年来的海面高度变化及其动力联系

利用卫星遥感和现场观测资料,结合线性Rossby波诊断解,研究了近20年热带太平洋和印度洋暖池区海面高度的快速升高趋势.结果表明,两大洋热带区域同步的海面上升趋势通过印度尼西亚海的海洋波导通道联系在一起,其动力关联主要发生在温跃层深度,表现为热带太平洋的海面高度低频波动信号通过印度尼西亚海传至印度洋,并影响到南印度洋的东部海区,而南印度洋西部的海面变化主要受印度洋内区局地风场的调制.超前-滞后相关分析的结果表明,东南印度洋海面高度的年际和年代际变化信号分别源自太平洋赤道和近赤道海区,分别受到了太平洋赤道风应力异常和近赤道风应力旋度异常的调控,并且分别与ENSO的年际过程和PDO的年代际过程密切相关.     

FGOALS－g快速耦合模式模拟的北太平洋年代际变率

本文分析了由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/IAP）最新发展的FGOALS_－g快速耦合模式300 a积分模拟结果,通过与多种观测资料的对比分析,讨论了北太平洋年代际变率的时空结构、主要年代际模态的演变特征以及与ENSO的联系等研究内容. 结果表明：该模式能成功模拟出北太平洋年代际变率的主要空间分布特征;模拟的年代际模态具有多时间尺度性,其中最显著的是周期约为10～20 a左右的准20年振荡模态,该模态上层海洋热容量异常的演变过程主要表现为大致沿副热带海洋涡旋做海盆尺度顺时针旋转的特征,相应的大气异常不仅与阿留申低压的变异有关,而且与太平洋-北美PNA）遥相关型以及上游的欧亚大气环流异常有密切关系;模拟的北太平洋年代际变率对年际ENSO循环的发生频率和强度有明显的调制作用. 但模拟的KOE区和阿拉斯加湾SST异常振幅比观测偏强,这与模式海冰偏多、高纬度SST偏冷的误差有关.     

Regional coupled ocean–atmosphere downscaling in the Southeast Pacific: impacts on upwelling, mesoscale air–sea fluxes, and ocean eddies

Ocean–atmosphere coupling in the Humboldt Current System (HCS) of the Southeast Pacific is studied using the Scripps Coupled Ocean–atmosphere Regional (SCOAR) model, which is used to downscale the National Center for Environmental Prediction (NCEP) Reanalysis-2 (RA2) product for the period 2000–2007 at 20-km resolution. An interactive 2-D spatial smoother within the sea-surface temperature (SST)–flux coupler is invoked in a separate run to isolate the impact of the mesoscale (～50–200 km, in the oceanic sense) SST field felt by the atmosphere in the fully coupled run. For the HCS, SCOAR produces seasonal wind stress and wind stress curl patterns that agree better with QuikSCAT winds than those from RA2. The SCOAR downscaled wind stress distribution has substantially different impacts on the magnitude and structure of wind-driven upwelling processes along the coast compared to RA2. Along coastal locations such as Arica and Taltal, SCOAR and RA2 produce seasonally opposite signs in the total wind-driven upwelling transport. At San Juan, SCOAR shows that upwelling is mainly due to coastal Ekman upwelling transport, while in RA2 upwelling is mostly attributed to Ekman pumping. Fully coupled SCOAR shows significant SST–wind stress coupling during fall and winter, while smoothed SCOAR shows insignificant coupling throughout, indicating the important role of ocean mesoscale eddies on air–sea coupling in HCS. Coupling between SST, wind speed, and latent heat flux is incoherent in large-scale coupling and full coupling mode. In contrast, coupling between these three variables is clearly identified for oceanic mesoscales, which suggests that mesoscale SST affects latent heat directly through the bulk formulation, as well as indirectly through stability changes on the overlying atmosphere, which affects surface wind speeds. The SST–wind stress and SST–heat-flux couplings, however, fail to produce a strong change in the ocean eddy statistics. No rectified effects of ocean–atmosphere coupling were identified for either the atmospheric or oceanic mean conditions, suggesting that mesoscale coupling is too weak in this region to strongly alter the basic climate state.     

Relationship between thermally forced surface wind and sea surface temperature gradient

An important part of the influence of the oceans on the atmosphere is through direct radiation, sensible heat flux and release of latent heat of evaporation, whereby all of these processes are directly related to the surface temperature of the oceans. A main effect of the atmosphere on the oceans is through momentum exchange at the air-ocean interface, and this process is directly related to the surface wind stress. The sea surface temperature (SST) and the surface wind stress are the two important components in the air-ocean system. If SST is given, a thermally forced boundary layer atmospheric circulation can be simulated. On the other hand, if the surface wind stress is given, the wind-driven ocean waves and ocean currents can be computed.The relationship between SST and surface wind is a coupling of the atmosphere and the oceans. It changes a one-way effect (ocean mechanically driven by atmosphere, or atmosphere thermally forced by oceans) into two-way air-sea interactions. Through this coupling the SST distribution, being an output from an ocean model, leads to the thermally forced surface winds, which feeds back into the ocean model as an additional forcing.Based on Kuo's planetary boundary layer model a linear algebraic equation is established to link the SST gradient with the thermally forced surface wind. The surface wind blows across the isotherms from cold to warm region with some deflection angle to the right (left) in the Northern (Southern) Hemisphere. Results from this study show that the atmospheric stratification reduces both the speed and the deflection angle of the thermally forced wind, however, the Coriolis' effect increases the wind speed in stable atmosphere (Ri>10^–4) and increases the deflection angle.     

斜压大气中热带气旋运动特征的动力分析

从绝热、无摩擦、无环境场作用条件下的原始方程组出发,讨论了热带气旋的动力平衡特征,并分别导出了正、斜压大气中综合描述热带气旋中心强度变化的物理量(dI/dt)及其动力平衡关系式,进而分析了正、斜压大气中的热带气旋强度变化及移动的特征.结果表明:热带气旋的定常运动具有"相当地转风平衡”的特征,其等"压能”线和等位涡线均与流线重合;"β涡旋对”及由高(低)层水平风正(负)垂直切变产生的"切变涡旋对”之间的"通风气流”均使热带气旋的强度减弱,高(低)层涡度的负(正)垂直平流则增强热带气旋的强度;热带气旋的中心有向极、向高(低)层涡度垂直平流的梯(升)度方向移动的趋势,垂直运动及高、低层水平风速垂直切变的非对称结构对热带气旋的移动有影响;"γ效应”则是"通风气流”牵引热带气旋移动的动力机制之一.     

On forecasting abnormal climatic events in the tropical Atlantic Ocean

Modelling and observational evidence indicate that interannual variabilities of dynamic height and sea surface temperature (SST) in the eastern part of the tropical Atlantic Ocean (Gulf of Guinea) are largely induced by preceding fluctuations in wind stress, mainly in the western equatorial basin. A wind-driven linear ocean model is used here to test the possibility of forecasting the abnormal dynamic heights. A control run of the model, forced by 1964–1993 wind stress monthly means, is first conducted. Yearly test runs (1964-1994) are subsequently performed from January to August by forcing the model with observed winds from January to May, and then by forcing with the May wind assumed to persist from June to August. During the last three decades the largest deviations of dynamic height simulated by the control run in the Gulf of Guinea in boreal summer would have been correctly forecast from wind data related only to conditions in May of each year. However, for weak climatic anomalies, the model may forecast overestimated values. For the most part (about 20 times during the last 30 years), the sign of the observed SST anomaly in the centre of the Gulf of Guinea during the boreal summer is identical to the sign of simulated anomalies of dynamic height deduced from both control and test runs. Along the eastern equatorial waveguide, the sea level forecasting skill slowly decreases from the first 2 weeks of June until the second 2 weeks of August, but remains high on both sides of the equator throughout boreal summer, as is expected from the adjustment in a linear ocean model. It is established that throughout the year in the Gulf of Guinea the accuracy of the 1-month forecast dynamic height anomaly provided by the simple linear method is greater than that of the 1-month forecast assuming persistence.     

Planetary Boundary Layer Flows in the Atmosphere and the Ocean at the Equator

—The boundary layer flows created by the frictional dissipation of the wind speed at the surface in the atmosphere and by surface wind stress in the ocean at the equator and in the equatorial region, are obtained by taking the influence of the surface friction on the zonal velocity as being balanced by vertical transport for the long-term mean flow and by a corresponding time variation for time-dependent flow fields. Solutions are expressed in terms of the velocities in zonal and vertical directions and the divergence of the horizontal current in the two media. It is found that under the ever present easterly flow in the lower atmosphere, the boundary layer flow in the atmosphere is convergence and ascending motion in the lower troposphere, and divergence at the surface and uplift in ocean, and in reverse directions for the westerly flow. Similar results are obtained for time-dependent wind fields and they give way to the steady asymptotic solutions when the period of the variation exceeds 10 months.     

Baroclinic and topographic influences on the transport in western boundary currents

Abstract

One of the central unsolved theoretical problems of the large scale ocean circulation is concerned with explaining the very large transports measured in western boundary currents such as the Gulf Stream and the Kuroshio. The only theory up to now that can explain the size of these transports is that of non-linear recirculation in which the advective terms in the momentum equations became important near the western boundary. In this paper an alternative explanation is suggested. When bottom topography and baroclinic effects are included in a wind-driven ocean model it is shown that the western boundary current can have a transport larger than that predicted from the wind stress distribution even when the nonlinear advective terms are ignored. The explanation lies in the presence of pressure torques associated with bottom topography which can contribute to the vorticity balance in the same sense as the wind stress curl.

Three numerical experiments have been carried out to explore the nature of this process using a three dimensional numerical model. The first calculation is done for a baroclinic ocean of constant depth, the second for a homogeneous ocean with an idealized continental slope topography, and the third for a baroclinic ocean with the same continental slope topography. The nature of the vorticity balance and of the circulation around closed paths is examined in each case, and it is shown that bottom pressure torques lead to enhanced transport in the western boundary current only for the baroclinic case with variable depth.     

武汉地区无线电探空仪加密观测的初步结果

利用武汉地区2006年1月11～15日的Radiosonde加密观测数据,本文讨论了当地对流层与低平流层（25 km以内）温度、纬向风与经向风周日潮汐变化的振幅与相位（振幅最大值对应的时间）的变化,同时与其他地区统计平均的结果进行了比较. 发现风场振幅的变化与统计平均的结果存在较大差异,这归结于当地冬季对流层内强烈变化而低平流层内相对稳定的风场;温度在23 km以上存在稳定的周日变化,气压在更大的范围内存在与温度类似的周日变化,这使得在23 km以上大气密度的周日变化十分微弱,在各个高度上近似为一个常数.     

A climatic dataset of ocean vertical turbulent mixing coefficient based on real energy sources

Using data on wind stress, significant height of combined wind waves and swell, potential temperature, salinity and seawater velocity, as well as objectively-analyzed in situ temperature and salinity, we established a global ocean dataset of calculated wind- and tide-induced vertical turbulent mixing coefficients. We then examined energy conservation of ocean vertical mixing from the point of view of ocean wind energy inputs, gravitational potential energy change due to mixing (with and without artificially limiting themixing coefficient), and K-theory vertical turbulent parameterization schemes regardless of energy inputs. Our research showed that calculating the mixing coefficient with average data and artificial limiting the mixing coefficient can cause a remarkable lack of energy conservation, with energy losses of up to 90% and changes in the energy oscillation period. The data also show that wind can introduce a huge amount of energy into the upper layers of the Southern Ocean, and that tidesdo so in regions around underwater mountains. We argue that it is necessary to take wind and tidal energy inputs into account forlong-term ocean climate numerical simulations. We believe that using this ocean vertical turbulent mixing coefficient climatic dataset is a fast and efficient method to maintain the ocean energy balance in ocean modeling research.     

Rectification of the wind-driven ocean circulation on the beta plane

Abstract

A nonlinear Stommel model of the ocean circulation on the beta plane, driven by a time periodic wind stress, is investigated in order to study symmetry properties of the observed time-mean ocean gyres. Due to the presence of vorticity advection terms the model will have a steady or rectified response to fluctuating wind fields. In this paper a small inverse Ekman number, “the small beta regime”, is considered. It is demonstrated that for this case all qualitative features of the residual circulation, obtained numerically by Veronis (1970). are reproduced in an analytical way. They include the dipole character of the gyre, its maximum symmetry breaking around the north-south axis for intermediate Reynolds numbers, measuring the ratio of vorticity forcing and dissipation, and the maximum residual response for intermediate forcing frequencies.