基于MTM-SVD方法的黄河流域夏季降水年际变化及其主要影响因子分析

应用中国气象台站积雪日数资料和NCEP/NCAR再分析资料以及多锥度—奇异值分解方法 (MTM-SVD),分析了近50年来黄河流域夏季降水的时空变化及其影响因子.发现黄河流域夏季降水存在显著的2～3年周期.在准3年周期上黄河流域夏季降水对前冬青藏高原东部积雪日数有很好的响应,当前冬高原积雪日数以正 (负) 异常为主时,接下来的夏季黄河流域降水偏少 (多).这种响应存在年代际变化,在1983年之前最为明显,1983~1993年是个调整时期,1993年以后又开始明显.在准2年周期上黄河流域夏季降水对前冬西太平洋暖池SST有很好的响应,当前冬西太平洋暖池SST偏高 (低) 时,接下来的夏季黄河流域降水表现为东多 (少)西少 (多) 型.这一响应同样存在年代际变化.前冬高原积雪和西太平洋暖池SST是影响黄河流域夏季降水的重要因子.     

开鲁盆地陆西凹陷热埋藏史研究

本文通过对有机质干酪根类型的分析，重新确定了陆面凹陷时间温度指数（ＴＴＩ）值计算的基准温度及古地温梯度，对凹陷内沉积厚度大的地方进行了沉积构造史的恢复，并建立了凹陷热埋藏史模式．据此计算了凹陷内部分ＴＴＩ值．通过研究，指出了目前对凹陷进行石油勘探的有利生油岩层位．     

Ray tracing for continuously rotated local coordinates belonging to a specified anisotropy

Conventional ray tracing for arbitrarily anisotropic and heterogeneous media is expressed in terms of 21 elastic moduli belonging to a fixed, global, Cartesian coordinate system. Our principle objective is to obtain a new ray-tracing formulation, which takes advantage of the fact that the number of independent elastic moduli is often less than 21, and that the anisotropy thus has a simpler nature locally, as is the case for transversely isotropic and orthorhombic media. We have expressed material properties and ray-tracing quantities (e.g., ray-velocity and slowness vectors) in a local anisotropy coordinate system with axes changing directions continuously within the model. In this manner, ray tracing is formulated in terms of the minimum number of required elastic parameters, e.g., four and nine parameters for P-wave propagation in transversely isotropic and orthorhombic media, plus a number of parameters specifying the rotation matrix connecting local and global coordinates. In particular, we parameterize this rotation matrix by one, two, or three Euler angles. In the ray-tracing equations, the slowness vector differentiated with respect to traveltime is related explicitly to the corresponding differentiated slowness vector for non-varying rotation and the cross product of the ray-velocity and slowness vectors. Our formulation is advantageous with respect to user-friendliness, efficiency, and memory usage. Another important aspect is that the anisotropic symmetry properties are conserved when material properties are determined in arbitrary points by linear interpolation, spline function evaluation, or by other means.     

Historical and future quantification of terrestrial carbon sequestration from a Greenhouse-Gas-Value perspective

Terrestrial ecosystems provide a range of important services to humans, including global and regional climate regulation. These services arise from natural ecosystem functioning as governed by drivers such as climate, atmospheric carbon dioxide mixing ratio, and land-use change. From the perspective of carbon sequestration, numerous studies have assessed trends and projections of the past and future terrestrial carbon cycle, but links to the ecosystem service concept have been hindered by the lack of appropriate quantitative service metrics. The recently introduced concept of the Greenhouse Gas Value (GHGV) accounts for the land-atmosphere exchanges of multiple greenhouse gases by taking into consideration the associated ecosystem pool sizes, annual exchange fluxes and probable effects of natural disturbance in a time-sensitive manner.We use here GHGV as an indicator for the carbon sequestration aspects of the climate regulation ecosystem service, and quantify it at global scale using the LPJ-GUESS dynamic global vegetation model. The response of ecosystem dynamics and ecosystem state variables to trends in climate, atmospheric carbon dioxide levels and land use simulated by LPJ-GUESS are used to calculate the contribution of carbon dioxide to GHGV. We evaluate global variations in GHGV over historical periods and for future scenarios (1850–2100) on a biome basis following a high and a low emission scenario.GHGV is found to vary substantially depending on the biogeochemical processes represented in LPJ-GUESS (e.g. carbon–nitrogen coupling, representation of land use). The consideration of disturbance events that occur as part of an ecosystem's natural dynamics is crucial for realistic GHGV assessments; their omission results in unrealistically high GHGV. By considering the biome-specific response to current climate and land use, and their projections for the future, we highlight the importance of all forest biomes for maintaining and increasing biogeochemical carbon sequestration. Under future climate and carbon dioxide levels following a high emission scenario GHGV values are projected to increase, especially so in tropical forests, but land-use change (e.g. deforestation) opposes this trend. The GHGV of ecosystems, especially when assessed over large areas, is an appropriate metric to assess the contribution of different greenhouse gases to climate and forms a basis for the monetary valuation of the climate regulation service ecosystems provide.     

江西九江-瑞昌震区的尾波衰减特征初探

根据单次散射模型,利用数字地震记录资料研究和讨论了江西省九江-瑞昌震区的尾波衰减特征,获得了可信的结果。经过计算,震中距30 km内的5个地震台站得到Q0值在75~79内波动。η值大体可以分为两类:九江台和范镇台η值为0.86~0.88;丁家山、狮子洞和武皎台η值为0.94~0.97,这种差别可能与台站方位有一定的关系。考虑到此次地震的破裂尺度不会太大,可采用后3个台的计算结果,拟合得到九江-瑞昌震区尾波Qc值随频率的变化关系为Qc(f)=(77.5±15.6)f0.96±0.09。九江-瑞昌震区的Q0值为77.5,η值为0.96,与云南武定、施甸地区接近,这种类似现象是构造运动活跃地区的特征体现还是反映了中强地震破裂区局部介质性质的一种共性,有待于进一步深入研究。本研究参与计算的5个台站最大尾波流逝时间为40~44 s,得到的平均采样体深度约为53 km,相对江西地区地壳平均厚度33 km而言,结果反映的是九江-瑞昌震区地壳和上地幔顶部的介质性质。     

基于Lowrank近似的TTI介质一步法qP波正演模拟

近年来,基于Lowrank近似的qP波正演模拟受到广泛关注。通常的Lowrank近似两步法波场外推虽然也能消除伪横波干扰,但是两步法依赖一个实值的相位函数,且在大时间步长不适用。基于Lowrank近似的qP波一步法波场外推方法具有处理复值相位函数的能力,对相位函数进行改进,加入速度梯度项,并成功应用于TTI介质qP波正演模拟。通过试验可知:基于Lowrank近似的一步法波场延拓具有传统两步法的优点,无伪横波干扰,在大时间步长波传播时比两步法更加稳定;各向异性情况下,一步法波场外推适用于任意倾角情况下,波场模拟结果清晰准确,没有发生不稳定。      

Numerical simulation of seismic wavefields in TTI media using the rotated staggered-grid compact finite-difference scheme

Numerical simulation in transverse isotropic media with tilted symmetry axis(TTI) using the standard staggered-grid finite-difference scheme(SSG)results in errors caused by averaging or interpolation. In order to eliminate the errors, a method of rotated staggered-grid finite-difference scheme(RSG) is proposed. However, the RSG brings serious numerical dispersion. The compact staggered-grid finite-difference scheme(CSG) is an implicit difference scheme, which use fewer grid points to suppress dispersion more effectively than the SSG. This paper combines the CSG with the RSG to derive a rotated staggered-grid compact finite-difference scheme(RSGC). The numerical experiments indicate that the RSGC has weaker numerical dispersion and better accuracy than the RSG.     

Numerical simulation of seismic wave in elastic and viscoelastic TTI media*

Based on the two-dimensional (2D) three-component first-order velocity-stress equation, the high order staggered mesh finite difference numerical simulation method was used to simulate the elastic and viscoelastic tilted transversely isotropic (TTI) media. The perfect matched layer (PML) absorption boundary condition was selected to eliminate the boundary effect. The results show that: ① Under the condition of fixed elastic parameters of elastic TTI medium, when the polarization angle and azimuth are 60° and 45° respectively, the degree of shear wave splitting is significantly greater than the angle of 0°; ② The influence of viscoelasticity on TTI medium is mainly reflected in the amplitude. If the quality factor decreases, the attenuation of the seismic wave amplitude increases, causing the waveform to become wider and distorted. If the quality factor increases, the viscoelastic medium becomes closer to elastic medium; ③ For TTI medium with different polarization angle and azimuth angle in the upper and lower layers, the shear wave can multiple splits at the interface of medium. The symmetry of seismograms is affected by the polarization angle and azimuth angle of TTI medium; ④ Viscoelasticity has a great influence on reflected wave, transmitted wave and converted wave in the low-velocity model. When the viscoelasticity is strong, the weaker waves may not be shown.     

Probabilistic analysis of the DoB in axially-loaded tubular KT-joints of offshore structures

The degree of bending (DoB) characterizing the through-the-thickness stress distribution has a profound effect on the fatigue behavior of tubular joints commonly found in steel offshore structures and the determination of DoB values is essential for improving the accuracy of fatigue life estimation. Probability density functions of the involved random variables are necessary for the fatigue reliability analysis of offshore structures. The objective of present research was the derivation of probability density function (PDF) for the DoB in tubular KT-joints commonly found in jacket-type offshore platforms. A total of 162 finite element (FE) analyses were carried out on 81 FE models of KT-joints subjected to two types of axial loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Based on the results of parametric FE study, a sample database was prepared for the DoB values and density histograms were generated for respective samples based on the Freedman-Diaconis rule. Thirteen theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov test was used to evaluate the goodness of fit. Finally, the Generalized Extreme Value model was proposed as the governing probability distribution function for the DoB. After substituting the values of estimated parameters, six fully defined PDFs were presented for the DoB in tubular KT-joints subjected to two types of axial loading.     

莱州湾湿地资源价值评估综合研究

文章分析了国内外资源价值评估现状及莱州湾湿地自然资源地理经济概况,构建了价值评估体系,运用价值评估方法对该湾湿地资源的直接和非直接使用价值进行评估计算,结果分别为449 640.5万元/a(其中,水产资源价值220 532万元/a,水资源价值73 887万元/a,原盐资源生产价值147 200万元/a,植物资源生产价值8 021.5万元/a)和85 972.6万元/a(其中,气候调节49 976万元/a,涵养水源27 515万元/a,湿地水质净化4 008万元/a,生物多样性维护4 473.6万元/a),发现水产资源、水资源、矿物资源、气候调节与涵养水源为莱州湾资源价值量较高的前5位。综上所述,本研究认为当地政府、企业及公众在发展经济的同时也应充分利用当地资源优势发展渔业与盐化工产业,以达资源可持续利用及生态保护之目的。