Ellipsoidal corrections to order e 2 of geopotential coefficients and Stokes’ formula     

L. E. Sjöberg 《Journal of Geodesy》2003,77(3-4):139-147

Assuming that the gravity anomaly and disturbing potential are given on a reference ellipsoid, the result of Sjöberg (1988, Bull Geod 62:93–101) is applied to derive the potential coefficients on the bounding sphere of the ellipsoid to order e ² (i.e. the square of the eccentricity of the ellipsoid). By adding the potential coefficients and continuing the potential downward to the reference ellipsoid, the spherical Stokes formula and its ellipsoidal correction are obtained. The correction is presented in terms of an integral over the unit sphere with the spherical approximation of geoidal height as the argument and only three well-known kernel functions, namely those of Stokes, Vening-Meinesz and the inverse Stokes, lending the correction to practical computations. Finally, the ellipsoidal correction is presented also in terms of spherical harmonic functions. The frequently applied and sometimes questioned approximation of the constant m, a convenient abbreviation in normal gravity field representations, by e ²/2, as introduced by Moritz, is also discussed. It is concluded that this approximation does not significantly affect the ellipsoidal corrections to potential coefficients and Stokes formula. However, whether this standard approach to correct the gravity anomaly agrees with the pure ellipsoidal solution to Stokes formula is still an open question.  相似文献   

Radon soil–gas as a geological mapping tool: case study from basement complex of Nigeria     

A. A. Adepelumi  T. R. Ajayi  B. D. Ako  A. O. Ojo 《Environmental Geology》2005,48(6):762-770

In an effort to quantify the geogenic radon soil–gas potential and appraise the use of radon technique as a geological mapping tool in a crystalline basement rock terrain of Ile–Ife Nigeria, radon measurement concentration were made using a radon detector instrument (EDA RD-200) that measures radon isotopes by a scintillator cell coupled to a photomultiplier tube. The data were collected from soils derived from three different lithologic rock units. The observed values were then correlated with the geology of the area. Significant differences in the radon soil–gas concentrations among the three geologic units were observed. Granite gneiss has the highest concentration, followed by grey gneiss and mica schist in that order. The geometric mean (GM) concentration of radon-222 measured in soils directly overlying the three different rock types were 301.4 pCi/l for granite gneiss, 202.8 pCi/l for the grey gneiss, and 199.4 pCi/l for mica schist. Conversely, the average values for radon-220 averaged 1510.0, 815.4, and 733.0 pCi/l for granite gneiss, grey gneiss, and mica schist rocks, respectively. Statistical t test (α=0.05) results indicated that there was no significant difference in the geometric mean of radon soil–gas measured between low and medium potential zones. However, significant differences were found between the low and high radon potential zones, and between the medium and high zones. The low concentrations of radon soil–gas emission observed in this study is explained in terms of the seasonal variation due to thermal convection fluid movement, while the radon concentrations were found to be controlled by the lithology and geochemistry of the underlying bedrock.  相似文献   

内核地球自转动力学理论的研究进展(Ⅰ)          下载免费PDF全文

张捍卫    许厚泽  王爱生 《地球物理学进展》2005,20(2):507-512

地球固体内核（SIC）和地球其余部分之间的引力和压力的耦合作用引起了一个力矩，从而对地球的章动运动产生影响.由于SIC的转动惯量和整体地球转动惯量相比是非常小的，因此可以认为SIC的动力学效应只是导致一个新的章动本征模，其频率与自由核章动（FCN）相差不太远，且对地球章动产生了一个微弱的共振影响.本文在文献〔1〕理论的基础上，对内核地球自转动力学理论进行了更加深入和详细的研究，顾及到高阶引潮力位的影响，介绍了研究内核地球自转的基本假设和定义，引潮力位的复数球函数表示，复数矢量球函数的基本理论等.  相似文献   

太湖北部沉积物重金属污染及其潜在生态危害评价   总被引：5，自引：0，他引：5  

黄顺生  范迪富陈宝 金洋 《江苏地质》2005,29(1):43-45

对太湖底北部表层20cm深沉积物样进行了重金属元素含量(Hg、Cd、Pb、Cu、Ni、Cr)分析，采用Hakanson潜在生态危害指数对其生态危害进行了评价：结果表明，沉积物表层5cm深以来Hg、Cd、Ph元素含量增加比较显著，生态危害指数比较高，构成了沉积物中等危害，其原因可能与太湖北部梅梁湾周围大量工业和生活废水未经处理直接排放相关。  相似文献   

北京市平原区地下水资源开采现状及评价   总被引：6，自引：3，他引：6  

贺国平  周东  杨忠山  赵泓漪  李慈君 《水文地质工程地质》2005,32(2):45-48

本文分析了北京市平原区地下水资源的开采现状,探讨了水资源开发利用过程中存在的问题。在分析平原区水文地质条件的基础上,采用FEFLOW软件建立了相应的地下水数值模拟模型,基于识别后的模型进行了水资源评价。研究表明:2000～2003年研究区地下水系统均衡分别为-7 73×108、-6 02×108、-5 95×108和-4 38×108m3,地下水系统的补给源主要是大气降水入渗补给和山前迳流补给,主要的排泄是人工开采。多年平均地下水补给资源量为22 98×108m3。平谷和昌平地区地下水还有开采潜力,密云-怀柔-顺义(密怀顺)平原和城近郊区地下水已过量开采。山前郊县地下水水质优良,城近郊区、大兴、房山和通州部分地区地下水水质较差。文章最后分析了引起地下水污染的主要原因。  相似文献   

确定辽东半岛潜在震源区的断层活动性研究          下载免费PDF全文

张裕明  国文秀  汪良谋 《地震地质》1987,9(1):35

本文讨论了在地震活动中等或较弱、而又没有发现古地震遗迹的地区(辽东半岛属于这类地区),如何利用断层活动性资料评价该区的地震危险性和确定潜在震源区的问题,并取得以下结果:1.该区发生的5级以上地震基本与晚更新世有过活动的断层有关;2.研究区活断层据其运动特性划分为以粘滑为主、蠕滑为主和粘滑、蠕滑兼有三类。6级地震发生在粘滑断层段;3.利用晚更新世活断层长度和个别断层的位移量估算了一些断层可能的最大震级  相似文献   

A statistical model for estimating the accuracy of event location applied to a network of Scandinavian stations   总被引：1，自引：0，他引：1  

Andrzej Kijko  Markvard A. Sellevoll 《Pure and Applied Geophysics》1982,120(1):186-196

A statistical model for estimating the errors of epicenter location and origin time is proposed and applied to the old Fennoscandian seismic network. An average crustal model (Sellevoll andPomeroy, 1968) and P and S wave residuals as a function of azimuth have been used. The calculations are carried out for different maximum detection ranges. The analysis shows relatively, small (1 km) standard errors of epicenter location of strong earthquakes for central Fennoscandia. The largest errors are found in the southern and eastern parts of Fennoscandia.On leave from Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland.  相似文献   

位涡倾向在Muifa台风路径转折中的应用   总被引：1，自引：0，他引：1  

袁敏  平凡  李国平 《大气科学》2018,42(2):281-291

利用ECMWF资料诊断分析了位涡倾向方程中的水平平流项和非绝热加热项分别在Muifa台风两次路径转折中的作用。结果表明:第一次路径转折过程中,非绝热加热项的量级比水平平流项小一个量级,水平平流项所表征的外部大尺度环流因素是第一次路径转折的主要原因;第二次路径转向过程由水平平流项和非绝热加热项共同控制,其中水平平流项控制台风的移向,非绝热加热项表征的内部非对称结构对台风转向有抑制作用。  相似文献   

一次飑线过程对流稳定度演变的诊断分析   总被引：5，自引：3，他引：2  

周围  包云轩  冉令坤  王勇 《大气科学》2018,42(2):339-356

针对2016年5月2日发生在华东地区的一次飑线过程,利用WRF模式进行高分辨率数值模拟。在成功模拟飑线发生、加强和移动的基础上,对此次过程中对流不稳定特征以及引起对流稳定度变化的原因进行诊断分析。结果表明:（1）在降水发生前,低层大气表现为对流不稳定;降水发生后,对流不稳定能量得到释放,大气趋于稳定。为了分析引起对流稳定度变化的原因,推导了局地直角坐标系中相当位温垂直梯度的倾向方程,其中位势散度是引起位势稳定度局地变化的主要强迫项。在弱降水区,低层位势散度为负值,有利于增强位势不稳定;强降水区及其前沿为位势散度正值区,倾向于抑制位势不稳定。在强降水区低层,位势散度的主要分量为垂直风切变项,代表垂直风切变和大气湿斜压性的综合作用;高层的主要分量为散度项,代表水平散度和位势稳定度的耦合作用。（2）位势散度能综合表征降水区上空垂直风切变、大气湿斜压性、水平辐合辐散和大气位势稳定度变化等特征,因而与降水联系紧密。本文利用位势散度对飑线降水进行预报,结果表明,位势散度与小时观测降水在时间和空间上吻合较好,对降水区有一定的指示意义,可以为飑线降水业务预报提供参考。  相似文献   

Comparison of wave load effects on a TLP wind turbine by using computational fluid dynamics and potential flow theory approaches     

《Applied Ocean Research》2015

Tension Leg Platform (TLP) is one of the concepts which shows promising results during initial studies to carry floating wind turbines. One of the concerns regarding tension leg platform wind turbines (TLPWTs) is the high natural frequencies of the structure that may be excited by nonlinear waves loads. Since Computational Fluid Dynamics (CFD) models are capable of capturing nonlinear wave loads, they can lead to better insight about this concern. In the current study, a CFD model based on immersed boundary method, in combination with a two-body structural model of TLPWT is developed to study wave induced responses of TLPWT in deep water. The results are compared with the results of a potential flow theory-finite element software, SIMO-RIFLEX (SR). First, the CFD based model is described and the potential flow theory based model is briefly introduced. Then, a grid sensitivity study is performed and free decay tests are simulated to determine the natural frequencies of different motion modes of the TLPWT. The responses of the TLPWT to regular waves are studied, and the effects of wave height are investigated. For the studied wave heights which vary from small to medium amplitude (wave height over wavelength less than 0.071), the results predicted by the CFD based model are generally in good agreement with the potential flow theory based model. The only considerable difference is the TLPWT mean surge motion which is predicted higher by the CFD model, possibly because of considering the nonlinear effects of the waves loads and applying these loads at the TLPWT instantaneous position in the CFD model. This difference does not considerably affect the important TLPWT design driving parameters such as tendons forces and tower base moment, since it only affects the mean dynamic position of TLPWT. In the current study, the incoming wave frequency is set such that third-harmonic wave frequency coincides with the first tower bending mode frequency. However, for the studied wave conditions a significant excitation of tower natural frequency is not observed. The high stiffness of tendons which results in linear pitch motion of TLPWT hull (less than 0.02 degrees) and tower (less than 0.25 degrees) can explain the limited excitement of the tower first bending mode. The good agreement between CFD and potential flow theory based results for small and medium amplitude waves gives confidence to the proposed CFD based model to be further used for hydrodynamic analysis of floating wind turbines in extreme ocean conditions.  相似文献