热带太平洋—印度洋温跃层海温异常联合模及其演变

利用SODA次表层海温再分析资料和卫星遥感海面高度异常数据,分析了热带太平洋和印度洋温跃层海温之间的联系,提出了太平洋—印度洋温跃层海温异常联合模(PITM)的概念、并定义了该联合模指数.结果表明,联合模指数具有准两年和3~5年的年际变化周期以及2011—2012年的年际变化周期,并具有季节锁相和振幅不对称等特征.联合模的演变过程与温跃层海温异常(TOTA)的发展和传播过程紧密相联:在太平洋,TOTA一般从西太平洋出发沿赤道(5°S—5°N)向东传播,到达东太平洋之后折向北,再沿10°N—14°N纬度带向西传播到达太平洋西岸并向赤道西太平洋扩展,形成一条回路;南太平洋也有类似回路但信号较弱;在印度洋,则主要沿8°S—12°S纬度带向西传播,到达西岸后折向北,然后迅速沿赤道(1.25°S—1.25°N)向东扩展,也形成一条回路.对NCEP/NCAR再分析风场资料的合成分析则表明,联合模的演变过程与大气环流尤其是纬向垂直环流(Walker环流)的变化密切相关,联合模的正位相对应着赤道印度洋区域顺时针的Walker环流以及赤道太平洋区域逆时针的Walker环流;而联合模的负相位则有相反的情况.此外,联合模演变过程中,TOTA的传播发展与850 hPa异常纬向风的传播发展有很好的相关.     

Changes in the mode of Southern Ocean circulation over the last glacial cycle revealed by foraminiferal stable isotopic variability

Benthic foraminiferal oxygen and carbon isotopic records from Southern Ocean sediment cores show that during the last glacial period, the South Atlantic sector of the deep Southern Ocean filled to roughly 2500 m with water uniformly low in δ¹³C, resulting in the appearance of a strong mid-depth nutricline similar to those observed in glacial northern oceans. Concomitantly, deep water isotopic gradients developed between the Pacific and Atlantic sectors of the Southern Ocean; the δ¹³C of benthic foraminifera in Pacific sediments remained significantly higher than those in the Atlantic during the glacial episode. These two observations help to define the extent of what has become known as the ‘Southern Ocean low δ¹³C problem’. One explanation for this glacial distribution of δ¹³C calls upon surface productivity overprints or changes in the microhabitat of benthic foraminifera to lower glacial age δ¹³C values. We show here, however, that glacial-interglacial δ¹³C shifts are similarly large everywhere in the deep South Atlantic, regardless of productivity regime or sedimentary environment. Furthermore, the degree of isotopic decoupling between the Atlantic and Pacific basins is proportional to the magnitude of δ¹³C change in the Atlantic on all time scales. Thus, we conclude that the profoundly altered distribution of δ¹³C in the glacial Southern Ocean is most likely the result of deep ocean circulation changes. While the characteristics of the Southern Ocean δ¹³C records clearly point to reduced North Atlantic Deep Water input during glacial periods, the basinal differences suggest that the mode of Southern Ocean deep water formation must have been altered as well.     

Inertial waves in a fluid partially filling a cylindrical cavity during spin-up from rest

Abstract

Inertial waves are excited in a fluid contained in a slightly tilted rotating cylindrical cavity while the fluid is spinning up from rest. The surface of the fluid is free. Since the perturbation frequency is equal to the rotation speed resonance occurs at a critical height to radius aspect ratio of the fluid. Detailed study of a particular inertial wave shows that in solid body rotation this “eigenratio” agrees with predictions from linear inviscid theory to within 0.5%. Measured time dependence of the eigenratio during spin-up from rest is a function of the tilt amplitude and agrees favorably with predictions from a numerical study. Mean flow associated with the inertial wave becomes unstable during spin-up and in the steady state. A boundary for the unstable region is found experimentally.     

Turning surface behaviour for internal waves subject to general gravitational fields

Abstract

It is shown that the turning surfaces associated with internal waves in a uniformly rotating, density stratified, Boussinesq fluid in the presence of an arbitrary gravitational field are regular points for the governing eigenvalue differential equation. The results are illustrated for two particular examples that have geophysical and astrophysical significance, namely radially directed spherical gravity, and the gravitational field in a rapidly rotating cylinder.     

On the steady mass transport induced by wave motions in a viscous rotating fluid

Abstract

The steady second-order motion induced by a first-order wave motion in a homogeneous, viscous and rotating fluid is examined. If the wave motion produces a steady Ekman layer suction by non-linear interactions, this suction must induce a steady component of interior, relative vorticity parallel to the axis of rotation in order to conserve mass. A boundary value problem for the determination of the induced, steady interior mass transport velocity is presented. The mass transport induced by a Kelvin wave is examined as an illustration and possible application of the theory.     

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.     

沁水盆地北部煤层气富集区CSAMT勘探试验研究

在分析沁水盆地北部煤层气富集与地下水和地质构造之间的关系基础上,采用大地电磁法探测地下水分布以及有利和不利煤层气富集影响因素、间接探测煤层气相对富集区;根据煤层气富集地质模型设计了地球物理模型,利用有限单元法开展典型薄层模型正演模拟,讨论了探测方法的可行性;选择山西沁水盆地北部煤层气勘探区开展可控源音频大地电磁探测技术试验,结合已有地质、钻井及测井资料完成了试验资料的处理与解释;试验结果表明,利用可控源音频大地电磁法能有效获得地层电性结构,推断含水、富水区,结合煤层气有利富集地质条件和影响因素,可以实现间接预测煤层气的有利富集区.     

The catastrophe structure of thermohaline convection in a two-dimensional fluid model and a comparison with low-order box models

Abstract

We impose a surface forcing on the 2D, Boussinesq, thermohaline equations in a rectangular domain, in the form of equatorially symmetric cosine distributions of salinity flux and temperature. This system may be seen as an idealization of the ocean thermohaline circulation on the global scale over intervals of centuries or millenia. Multiple steady states are found numerically. They reflect the competition between the opposite signs of the temperature and salinity-driven equatorially symmetric circulations. There are also pole-to-pole, equatorially asymmetric circulations. In the control space of the temperature and salinity-flux forcing amplitudes, these equilibria form two cusp catastrophes, and transitions between stable equilibria occur through several distinct bifurcations. These catastrophes can be reproduced in simple box models connecting stirred reservoirs through capillary pipes. This steady-state analysis may provide a framework for a better understanding of climatic transitions between different stable regimes of the ocean-atmosphere system.     

全球纬向平均大气环流基本模态年代际变化的凝聚小波分析

应用1871—2008年NCEP／NCAR月平均再分析资料,研究了1948—2008年期间全球纬向平均大气环流基本模态的年代际变化.小波凝聚谱的结果表明全球纬向平均大气环流基本模态存在显著的20年左右周期的年代际变化.小波凝聚位相的结果清楚地显示了纬向平均大气环流基本模态的变化顺序.在20年左右的年代际变化时间尺度上,全球纬向平均温度超前纬向平均位势高度2个月,同时超前纬向平均流10个月出现变化;全球纬向平均位势高度又超前纬向平均流8个月出现变化.全球温度上升(下降), 将使高纬度的纬向平均位势高度降低(升高),中低纬度的纬向平均位势高度升高(降低);进而使得中高纬和热带的纬向平均西风加(减)速或东风减(加)速,同时使极地和副热带的西风减(加)速或东风加(减)速.20世纪70年代末期以来全球显著增暖的异常信号最早出现在南半球对流层顶附近,其次出现在南半球对流层低层、北半球对流层顶附近和北半球对流层低层.     

Effects of a variety of Indian Ocean surface temperature anomaly patterns on the summer monsoon circulation: Experiments with the NCAR general circulation model

The time mean response of the summer monsoon circulation, as simulated by the 2.5° latitude-longitude resolution, July version of the National Center for Atmospheric Research (NCAR) General Circulation Model (GCM), to a variety of Indian Ocean surface temperature anomaly patterns is examined. In separate experiments, prescribed changes in surface temperature are imposed in the Western Arabian Sea, the Eastern Arbian Sea or the Central Indian Ocean. The influence of these anomaly patterns on the simulated summer monsoon circulation is evaluated in terms of the geographical distribution of the prescribed change response for any field of interest. This response is defined as the grid point difference between a 30-day mean from a prescribed change experiment and the ensemble average of the 30-day means from the control population for which the same set of climatological ocean surface temperatures are used in each simulation. The statistical significance of such a prescribed change response is estimated by relating the normalized response (defined as the ratio of the prescribed change response to the standard deviation of 30-day means as estimated from the finite sample of control cases) to the classical Student'st-statistic. Using this methodology, the most prominent and statistically significant features of the model's response are increased vertical velocity and precipitation over warm anomalies and typically decreased vertical velocity and precipitation in some preferred region adjacent to the prescribed change region. In the case of cold anomalies, these changes are of opposite sign. However, none of the imposed anomaly patterns produces substantial or statistically significant precipitation changes over large areas of the Indian sub-continent. The only evidence of a major nonlocal effect is found in the experiment with a large positive anomaly (+3°C) in the Central Indian Ocean. In this instance, vertical velocity and precipitation are reduced over Malaysia and a large area of the Equatorial Western Pacific Ocean. Thus, while these anomaly experiments produce only a local response (for the most part), it is hoped, as one of the purposes of the planned Monsoon Experiment (MONEX), that the necessary data will be provided to produce detailed empirical evidence on the extent to which Indian Ocean surface temperature anomalies correlate with precipitation anomalies over the Indian subcontinent—a correlation which generally does not appear in these GCM results.The National Center for Atmospheric Research is sponsored by the National Science Foundation     

Internal Variability Of The North Atlantic Wind-Driven Ocean Circulation

A new approach to understand the physical processes that govern internal variability of the large scale North Atlantic ocean circulation is outlined and current methods and results are reviewed. In this approach, based on the theory of dynamical systems, internal variability is viewed as arising through successive transitions when parameters are changed. The potential of the approach is demonstrated through analysesof solutions of intermediate complexity models of the wind-driven ocean circulation in the North Atlantic. In a quasi-geostrophic modelfor the flow in a rectangular basin with idealized wind forcing, the basic transitions are already found and physical mechanisms at work can be described in detail. Qualitatively, this transition behavior remains robust in more realistic models, having shallow water dynamics, realistic wind forcingand continental geometry, although patterns and time scales changethrough the model hierarchy. The relevance of the results is discussed inrelation to those of observations and of ocean general circulation models.     

土-结构体系的分枝模态与约束模态混合二步法

为了在结构设计过程中考虑土-结构非线性相互作用的影响,在线性-非线性混合的约束模态法以及分枝模态法的基础上,提出了适用于土-结构非线性相互作用体系的分枝模态与约束模态的混合方法,该方法既可考虑土体和结构的非线性特性又便于考察土-结构相互作用对上部结构的影响。在分枝模态与约束模态混合方法的基础上,进一步提出了混合二步分析法,并将其应用到地基土-框架结构地震响应分析中,算例结果表明,混合二步分析法在实现上部结构和地基土分开计算的同时,还能够考虑结构与地基土的材料非线性特性,有利于采用专业设计软件仅通过对上部结构进行分析来考虑土-结构相互作用的影响,为实际工程计算考虑土-结构相互作用的影响提供了便利的条件。     

模态静力非线性分析中模态选择的研究

本文应用模态静力非线性分析方法,对多个算例进行了静力非线性分析。比较分析了不同振型组合对计算精度的影响,对模态选择的参数进行了研究,提出采用模态质量参与系数进行模态选择的控制,为模态静力非线性分析方法的推广使用提供参考。另外,分析了结构基本周期对该方法计算精度的影响。     

Oscillating glacial northern and southern deep water formation from combined neodymium and carbon isotopes

While ocean circulation is driven by the formation of deep water in the North Atlantic and the Circum-Antarctic, the role of southern-sourced deep water formation in climate change is poorly understood. Here we address the balance of northern- and southern-sourced waters in the South Atlantic through the last glacial period using neodymium isotope ratios of authigenic ferromanganese oxides in thirteen deep sea cores from throughout the South Atlantic. The data indicate that northern-sourced water did not reach the Southern Ocean during the late glacial, and was replaced by southern-derived intermediate and deep waters. The high-resolution neodymium isotope record (~ 300 yr sample spacing) from two spliced deep Cape Basin sites indicates that over the last glacial period northern-sourced water mass export to the Southern Ocean was stronger during the major Greenland millennial warming intervals (and Southern Hemisphere cool periods), and particularly during the major interstadials 8, 12, and 14. Northern-sourced water mass export was weaker during Greenland stadials and reached minima during Heinrich Events. The benthic foraminiferal carbon isotopes in the same Cape Basin core reflect a partial control by Southern Hemisphere climate changes and indicate that deep water formation and ventilation occurred in the Southern Ocean during major Greenland cooling intervals (stadials). Together, neodymium isotopes and benthic carbon isotopes provide new information about water mass sourcing and circulation in deep Southern Ocean waters during rapid glacial climate changes. Combining carbon and neodymium isotopes can be used to monitor the relative proportion of northern- and southern-sourced waters in the Cape Basin to gain insight into the processes which control the carbon isotopic composition of deep waters. In this study we show that deep water formation and circulation was more important than biological productivity and nutrient regeneration changes for controlling the carbon isotope chemistry of Antarctic Bottom Water during millennial-scale glacial climate cycles. This observation also lends support to the hypothesis that ocean circulation is linked to interhemispheric climate changes on short timescales, and that ventilation in the glacial ocean rapidly switched between the northern and Southern Hemisphere on millennial timescales.     

Fluxes of fluid and heat from the oceanic crustal reservoir

Recent discoveries define a global scale fluid reservoir residing within the uppermost igneous oceanic crust, a region of seafloor that is both warm and may harbor a substantial biosphere. This hydrothermal fluid reservoir formed initially within volcanic rocks newly erupted at mid-ocean ridges, but extends to the vastly larger and older ridge flanks. Upper oceanic crust is porous and permeable due to the presence of lava drainbacks, fissuring, and inter-unit voids, and this porosity and permeability allows active fluid circulation to advect measurable quantities of lithospheric heat from the crust to an average age of 65 Myr. A compilation of crustal porosities shows that this fluid reservoir contains nearly 2% of the total volume of global seawater. Heat flow and sediment thickness data allow calculation of reservoir temperatures, predicting 40°C mean temperatures in Cretaceous crust. Utilizing these temperature estimates, heat flow measurements and models for the thermal structure and evolution of the oceanic lithosphere, we have computed mean hydrothermal fluxes into the deep ocean as a function of plate age. The total hydrothermal volume flux into the oceans approaches 20% of the total riverine input and may contribute to the global seawater mass balance.     

基于经验模态分解的地震瞬时属性提取

传统复地震道方法提取的地震瞬时属性存在物理意义不明确、对噪声敏感等不足,本文探讨基于经验模态分解的地震瞬时属性提取方法,得到不同尺度下的地震瞬时属性,由此得到的瞬时频率在数值上与地震主频对应较好.将该方法提取的属性应用到海上地震数据中,显示出较好的效果.     

基于振型的结构平面规则性界定方法

为研究结构平面规则性的界定方法,首先分析了平面规则结构的振型序列特征并验证了其稳定性。以L型结构为例,通过将规则结构的振型序列特征与L型结构的振型序列特征对比,得到了不同L型结构的平面规则性界定曲线,指出了凸出部分的横向长度与横向总长度之比、凸出部分的纵向长度与纵向总长度之比和结构高度是影响L型结构平面规则与否的重要因素,并建议平面不规则结构位移比限值取1.3。提出了基于振型的结构平面规则性界定方法,即:与平面规则结构的振型序列相比,平面不规则结构的振型序列中不利振型（扭转振型、包含扭转的耦合振型及局部振型等需考虑空间效应的振型）会提前。通过对一实际结构进行计算分析,验证了基于振型的结构平面规则性界定方法的优越性和正确性。     

用应变模态技术诊断梁结构的损伤

重点研究损伤对应变模态影响规律及其灵敏程度.根据计算结果,损伤处附近发生突变,损伤30%时突变区为梁长的12.5%.应变模态对非节点损伤非常敏感,应变模态也有明显改变,尤其是跨中损伤第1阶、四分之一跨损伤第3和第2阶.跨中损伤时,1阶应变模态除突变区外大多数应变几乎呈均匀下降趋势.四分之一跨损伤30%时,3阶应变模态第1峰值区及2阶模态第1、第2峰值区应变振型值下降至58.6%、71.9%及84.2%.所以,可利用应变模态的敏感性确定损伤位置和程度.     

On the normal mode instability of harmonic waves on a sphere

Abstract

The normal mode instability of harmonic waves in an ideal incompressible fluid on a rotating sphere is analytically studied. By the harmonic wave is meant a Legendrepolynomial flow αP_n(μ) (n ≥ 1) and steady Rossby-Haurwitz wave of set F ₁ ⊕ H_n where H_n is the subspace of homogeneous spherical polynomials of the degree n(n ≥ 2), and F ₁ is the one-dimensional subspace generated by the Legendre-polynomial P₁(μ). A necessary condition for the normal mode instability of the harmonic wave is obtained. By this condition, Fjörtoft's (1953) average spectral number of the amplitude of each unstable mode must be equal to . It is noted that flow αP_n (μ) is Liapunov (and hence, exponentially and algebraically) stable to all the disturbances whose zonal wavenumber m satisfies condition |m| ≥ n. The bounds of the growth rate of unstable normal modes are estimated as well. It is also shown that the amplitude of each unstable, decaying or non-stationary mode is orthogonal to the harmonic wave.

The new instability condition can be useful in the search of unstable perturbations to a harmonic wave and on trials of numerical stability study algorithms. For a Legendre-polynomial flow, it complements Kuo's (1949) condition in the sense that while the latter is related to the basic flow structure; the former characterizes the structure of a growing perturbation.