热带印度洋秋季偶极子模态与南海夏季风强度变化的关系   总被引：2，自引：1，他引：2  

李东辉  张瑰  朱益民  谭言科  王学忠 《热带气象学报》2006,22(5):439-446

利用多年的Reynolds月平均海表温度资料和NCEP／NCAR全球大气再分析资料，采用经验正交函数（EOF）分析和滑动相关方法，研究了热带印度洋秋季偶极子模态和南海夏季风强度变化的关系。结果表明：（1）热带印度洋秋季海表温度距平（SSTA）的主要模态是全区一致型和偶极子（IOD）型，全区一致型模态主要代表了秋季SSTA全海盆一致的年代际及其以上时间尺度的变化，IOD型模态主要反映热带印度洋秋季SSTA年际时间尺度的变化。（2）当前期秋季热带印度洋存在正（负）IOD模态时，南海的夏季风强度减弱（增强）。二者年际变化的负相关关系在长期趋势的冷位相期不显著，而在暖位相期显著。（3）当南海夏季风强度增强（减弱）时，后期秋季热带印度洋出现正（负）IOD模态。二者年际变化的正相关关系在长期趋势的冷、暖位相期显著，在冷、暖位相转换期前后不显著。  相似文献   

大平山铜矿毒砂单矿物扫描电镜分析   总被引：2，自引：0，他引：2       下载免费PDF全文

王少华  汪斌  徐兆文 《江苏地质》2012,36(2):119-128

大平山铜矿床位于南京市江宁区横溪镇西侧,矿石中有用组分除铜以外,还伴生有As、Zn、Ag、Au、Co和Ni等元素,其中As元素质量分数较高,局部达0.2%～0.9%。通过显微观察和扫描电镜能谱分析,发现大平山铜矿矿石中As元素主要以硫化物形式,呈毒砂独立矿物以自形—半自形粒状、他形粒状赋存于矿石中。赋存方式主要为：以独立矿物呈稀疏浸染状分布于矿石中,局部呈条带状和中等稠密浸染状分布于矿石中;以交代方式与黄铁矿和黄铜矿共生于矿石中,但毒砂形成晚于黄铁矿和黄铜矿。  相似文献   

框架结构楼顶通信塔的地震响应分析     

王元德  刘爱文 《震灾防御技术》2016,11(3):552-560

通信塔通常架设在已有的建筑物上。在地震中,建在屋顶上高耸的通信塔鞭梢效应比较显著,常常受到严重的破坏,而通信塔的损坏将会影响震后救灾工作的开展。本文基于通信塔的实际震例,分析了通信塔出现鞭梢效应的主要原因。采用振型分解反应谱法和线性时程分析法,分析了位于不同层数框架结构上的两个通信塔的地震作用。结果表明通信塔和框架结构的自振周期接近时是鞭梢效应最容易发生的时刻,两者的一阶特征周期接近时鞭梢效应最大;场地特征周期越大,通信塔的地震效应越大。  相似文献   

黄土高原100万年以来东亚夏季风演变信号的多尺度分析   总被引：1，自引：0，他引：1  

杨周  林振山  俞鸣同  张真真 《地理与地理信息科学》2008,24(5)

在研究黄土高原东亚季风地质时期周期演变中,利用经验模态分解(EMD)方法对黄土高原甘肃省灵台和赵家川黄土剖面约1 MaB.P.以来磁化率时间序列进行多尺度变化分析,结果表明:1)0~0.8 MaB.P.地球轨道三要素中的偏心率准400 ka、100 ka周期在黄土沉积中反映明显,方差贡献率达35.19%,还发现16 ka的岁差周期及334 ka1、77 ka5、8 ka、31 ka、7.9 ka、3.9 ka的非轨道准周期;2)0.8~1 MaB.P.也发现地球轨道三要素中的偏心率准100 ka周期2、1 ka岁差周期及55 ka、8.3 ka、3.5 ka非轨道准周期,偏心率准100 ka周期具有主导地位(方差贡献率达37.44%);3)尽管黄土记录的东亚夏季风100 ka周期的产生机制已有多种假说,古气候学界还是普遍认为它产生于某些尚不清楚的过程,有待进一步研究。  相似文献   

Recent Sea Level and Sea Surface Temperature Changes Along the Maldives Coast     

O. P. Singh  Tariq Masood Ali Khan  Fahmida Aktar  Majajul Alam Sarker 《Marine Geodesy》2013,36(4):209-218

Maldives, a South Asian small island nation in the northern part of the Indian Ocean is extremely vulnerable to the impacts of Sea Level Rise (SLR) due to its low altitude from the mean sea level. This artricle attempts to estimate the recent rates of SLR in Maldives during different seasons of the year with the help of existing tidal data recorded in the Maldives coast. Corresponding Sea Surface Temperature (SST) trends, utilizing reliable satellite climatology, have also been obtained. The relationships between the SST and mean sea level have been comprehensively investigated. Results show that recent sea level trends in the Maldives coast are very high. At Male, the capital of the Republic of Maldives, the rising rates of Mean Tidal Level (MTL) are: 8.5, 7.6, and 5.8 mm/year during the postmonsoon (October-December), Premonsoon (March-May) and southwest monsoon (June-September) seasons respectively. At Gan, a station very close to the equator, the increasing rate of MTL is maximum during the period from June to September (which is 6.2 mm/year). These rising trends in MTL along the Maldives coast are certainly alarming for this small developing island nation, which is hardly one meter above the mean sea level. Thus there is a need for careful monitoring of future sea level changes in the Maldives coast. The trends presented are based on the available time-series of MTL for the Maldives coast, which are rather short. These trends need not necessarily reflect the long-term scenario. SST in the Maldives coast has also registered significant increasing trend during the period from June to September. There are large seasonal variations in the SST trends at Gan but SST and MTL trends at Male are consistently increasing during all the seasons and the rising rates are very high. The interannual mode of variation is prominent both in SST as well as MTL. Annual profile of MTL along the Maldives coast is bimodal, having two maxima during April and July. The April Mode is by far the dominant one. The SST appears to be the main factor governing the sea level variations along the Maldives coast. The influence of SST and sea level is more near the equatorial region (i.e., at Gan). There is lag of about two months for the maximum influence of SST on the sea level. The correlation coefficient between the smoothed SST and mean tidal level at Gan with lag of two months is as high as ~ +0.8, which is highly significant. The corresponding correlation coefficients at Male with the lags of one and two months are +0.5 and +0.3, respectively. Thus, the important finding of the present work for the Maldives coast is the dominance of SST factor in sea level variation, especially near the region close to the equator.  相似文献   

Assessment of structural stability in Bohai Sea area based on AHP-GDM model     

XIU Zongxiang  LIU Baohu  XIE Qiuhong  LI Xishuang  LIU Chenguang  PEI Yanliang  ZHENG Yanpeng 《海洋学报(英文版)》2013,32(4):41-48

The AHP-GDM model is used for the assessment of structural stability, with the Bohai Sea area as an example. In this model, the credit degree of each expert is calculated through the assessment matrix based on the similarity and diversity of vector. The comprehensive opinions of expert panel are quantitatively obtained by considering the effect of credit degree. According to the geological structural setting, the Bohai Sea is divided into twelve assessment zones of structural stability by non-uniform element method. The structural stability grade of each zone is obtained on the basis of the latest geophysical data, earthquake statistical data, and the information of fault activities, current stress field and crustal deformation. The results show that there are one relatively stable area, three relatively sub-stable areas, six relatively sub-unstable areas and two relatively unstable areas. The assessment results of non-uniform element method are very close with those of uniform grid method with size of 0.25° in longitude direction and 0.14° in latitude direction. However the workload of non-uniform element method is only 1/16 of the latter. Compared with traditional assessment methods of structural stability, a more objective and reliable assessment result can be obtained by combining non-uniform element method and AHP-GDM model.  相似文献   

Modal identification of a centrifuge soil model using subspace state space method     

《Soil Dynamics and Earthquake Engineering》2016

In this paper, modal parameters of a layered soil system comprising of a soft clay layer overlying a dense sand layer are identified from accelerometer recordings in a centrifuge test. For the first time, the subspace state space system identification (4SID) method was employed to identify the natural frequencies, damping ratios, and complex valued mode shapes while considering the non-proportional damping in a soil system. A brief review of system identification concepts needed for application of the 4SID techniques to structural modal identification is provided in the paper. The identified natural frequencies were validated against those estimated by transfer function spectra. The computed normal mode shapes were compared with closed-form solutions obtained from the one-dimensional shear wave propagation equation. The identified modal parameters were then employed to synthesize state space prediction models which were subsequently used to simulate the soil response to three successive base motions. The identified models captured acceleration time-histories and corresponding Fourier spectra reasonably well in the small and moderate shaking events. In the stronger third shaking event, the model performed well at greater soil depths, but was less accurate near the surface where nonlinearities dominated.  相似文献   

Efficient subset simulation for evaluating the modes of improbable slope failure     

《Computers and Geotechnics》2017

For analyzing low probability slope failures, a modified version of subset simulation, based on performance-based subset selection rather than the usual probability-based subset selection, is combined with the random finite element method. The application to an idealized slope is used to study the efficiency and consistency of the proposed method compared to classical Monte Carlo simulations and the shear strength reduction (SSR) method. Results demonstrate that failure events taking place without strength reduction have different modes of failure than stable slopes brought to failure by SSR. The correlation between sliding volume and factor of safety is also demonstrated.  相似文献   

一种去除地震背景噪音的新方法   总被引：1，自引：1，他引：0  

杨光亮 《大地测量与地球动力学》2011,31(4):90-93

结合希尔伯特-黄变换方法,根据信号背景噪音时间延续性假设,提出了一种自适应地震信号去噪算法。利用该算法实现了台站地震监测信号的去噪分析。分析表明：1）该去噪算法能根据背景信号特性有效去除信号的低频干扰;2）该算法可自适应完成信号分解去噪,计算效率高,无时间分辨率和频率分辨率问题;3）该算法处理高频干扰存在缺陷,有待进一步完善。  相似文献   

地震海洋学方法在海洋混合参数提取中的研究与应用——以南海内波和地中海涡旋为例   总被引：2，自引：1，他引：1       下载免费PDF全文

拜阳  宋海斌  董崇志  刘伯然  陈江欣  耿明会 《地球物理学报》2015,58(7):2473-2485

混合是海洋中普遍存在的一种海水运动形式,对多个海洋学分支的研究具有重要的影响.随着物理海洋学的研究重心从大尺度向中小尺度现象过渡,近年来混合问题的研究重心也逐渐转向了中小尺度现象.内波与中尺度涡都是非常重要的中小尺度物理海洋学现象,对海洋能量在不同尺度中的级联发挥着重要的作用.本文基于地震海洋学研究了海洋混合参数的提取方法,并以南海内波和地中海涡旋为例进行了计算和分析.结果显示,南海内波在200~600m深度范围内所引起的混合可达10-2.79 m2·s-1左右,比大洋的统计结果10-5 m2·s-1高出两个数量级以上.而地中海涡旋所引起的湍流混合率可达10-3.44 m2·s-1左右,与大洋统计结果相比高出1.5个数量级左右,并且地中海涡旋下边界的混合要强于上边界,这一特征与前人的研究一致,另外涡旋上边界之上以及侧边界的外侧也具有非常高的混合率.  相似文献