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1.
We have analyzed the regularities in the spatiotemporal behavior of the methane concentration and mass, recorded in different
regions of the globe. In the southern hemisphere (SH), the methane concentration does not depend on latitude. In the northern
hemisphere (NH), the methane concentration increases towards the Arctic zone. The maximum CH4 concentration in the fall is due to the action of the additional methane sources in the NH Arctic region. The methane flux
calculations showed that in the SH the methane flux into the Earth’s atmosphere is barely season dependent. In the NH during
the fall season, the methane flux considerably increases, and the difference between the maximum flux in August-September
and the flux in December-January reaches three. The additional, still disregarded sources, sustaining high methane emission
in the spring season at high SH latitudes are estimated to be as strong as 100–120 Tg per year. To equilibrate the methane
supply to the atmosphere and methane sink in SH, additional, yet unidentified sources of over 300 Tg/yr are required. The
global methane flux into the Earth’s atmosphere should be no less than 1050–1100 Tg yearly. 相似文献
2.
Rayleigh’s method of approximation is employed to find out the reflection and transmission coefficients due to an incident
plane SH wave at a corrugated interface between a laterally and vertically inhomogeneous anisotropic elastic solid half-space
and a laterally and vertically inhomogeneous isotropic visco-elastic solid half-space. The lateral and vertical inhomogeneities
are described by the exponential variations of elastic parameters. The formulae of reflection and transmission coefficients
are derived in closed form for the first-order approximation of the corrugation. The effects of the corrugation of the interface,
the inhomogeneity, the anisotropy, the visco-elasticity and the frequency of the incident wave on these coefficients are studied
analytically and numerically for a specific model containing a periodic interface. The results of earlier workers have been
reduced as particular cases from the present formulation. 相似文献
3.
《Advances in water resources》2004,27(6):657-667
In this article, the quadrupole method is implemented in order to simulate the effects of heterogeneities on one dimensional advective and diffusive transport of a passive solute in porous media. Theoretical studies of dispersion in heterogeneous stratified media can bring insight into transport artefacts linked to scale effects and apparent dispersion coefficients. The quadrupole method is an efficient method for the calculation of transient response of linear systems. It is based here on the Laplace transform technique. The analytical solutions that can be derived by this method assists understanding of upscaled parameters relevant to heterogeneous porous media.First, the method is developed for an infinite homogeneous porous medium. Then, it is adapted to a stratified medium where the fluid flow is perpendicular to the interfaces. The first heterogeneous medium studied is composed of two semi-infinite layers perpendicular to the flow direction each having different transport properties. The concentration response of the medium to a Dirac injection is evaluated. The case studied emphasises the importance in the choice of the boundary conditions.In the case of a periodic heterogeneous porous medium, the concentration response of the medium is evaluated for different numbers of unit-cells. When the number of unit cells is great enough, depending on the transport properties of each layer in the unit cell, an equivalent homogeneous behaviour is reached. An exact determination of the transport properties (equivalent dispersion coefficient) of the equivalent homogeneous porous medium is given. 相似文献
4.
声波测井仪器的等效理论及其应用(英文) 总被引：3，自引：0，他引：3
在处理实际声波测井模式波数据或用模式波的反演地层参数时,必须考虑测井仪器对频散模式波传播的影响。本文介绍了一种用具有等效弹性模量的圆柱体来模拟声波测井仪器的等效理论,并将该理论推广应用到电缆、随钻多极子声波测井。在波长大于仪器半径的前提下,将井中的多极子声场与该等效仪器模型进行声导纳/阻抗匹配,便可导出这一理论。通过数值模拟和现场资料对该理论的有效性和实用性进行了验证,验证结果证明该理论既简单又足够精确。利用该理论模型处理实际资料时,通过调整仪器等效弹性模量和半径在给定频段标定仪器的影响,而不必考虑仪器的具体材料和结构。本文以电缆偶极子声波测井现场资料的频散校正为例,进一步证明了该等效理论处理现场资料的准确性和高效性。 相似文献
5.
Effect of point source and heterogeneity on the propagation of SH-Waves in a viscoelastic layer over a viscoelastic half space 总被引：1，自引：1，他引：0
The present paper is concerned with the propagation of shear waves in a homogeneous viscoelastic isotropic layer lying over
a semi-infinite heterogeneous viscoelastic isotropic half-space due to point source. The inhomogeneity parameters associated
to rigidity, internal friction and density are assumed to be functions of depth. The dispersion equation of shear waves has
been obtained using Green’s function technique. The dimensionless angular frequency has been plotted against dimensionless
wave number for different values of inhomogeneity parameters. The effects of inhomogeneity have been shown in the dispersion
curves. graphical user interface (GUI) software in MATLAB has been developed to show the effect of various inhomogeneity parameters
on angular frequency. The topic can be of interest for geophysical applications in propagation of shear waves on the Earth’s
crust. 相似文献
6.
The studies on the structure and physical properties of the Earth‘s interior done by Chinese geophysicists from 1999 to 2002 were reviewed in this paper. It includes several research areas: the structure of the Earth‘s interiors using seismic tomography, anisotropy of the upper mantle in China and its adjacent areas, quality factor Qβ for S waves, subduction zone, mantle discontinuities, physical properties of Earth‘s materials and others. The review concerns mainly the contents, the methods and the results of the studies. It can be seen that new progress in the study on the structure and physical properties of the Earth‘s interior has been made in the last 4 years in China. It is shown on three aspects: advancement made on some preexistent areas; pioneering on some new fields and new methods adopted. 相似文献
7.
Modeling transport of contaminants in the earths subsurface relies on numerical solutions over grids with blocks larger than Darcys scale. The hydraulic conductivity is homogenized over the grid blocks and the plumes spreading is reduced as a consequence of the wiped-out variability. To compensate for this loss Rubin et al. (1999) proposed to augment mixing by block-effective dispersion coefficients, and Rubin et al. (2003) showed, by means of two dimensional simulations, how this concept can be applied in practice. In this paper, we present new solutions of the block-effective dispersion tensor for an axisymmetric exponential covariance model. In addition, we discuss the influence of pore-scale dispersion in both two- and three-dimensional applications. 相似文献
8.
Cities’ ability reducing earthquake disasters is a complex system involving numerous factors, moreover the research on evaluating
cities’ ability reducing earthquake disasters relates to multi-subject, such as earthquake science, social science, economical
science and so on. In this paper, firstly, the conception of cities’ ability reducing earthquake disasters is presented, and
the ability could be evaluated with three basic elements — the possible seismic casualty and economic loss during the future
earthquakes that are likely to occur in the city and its surroundings and time required for recovery after earthquake; based
upon these three basic elements, a framework, which consists of six main components, for evaluating city’s ability reducing
earthquake disasters is proposed; then the statistical relations between the index system and the ratio of seismic casualty,
the ratio of economic loss and recovery time are gained utilizing the cities’ prediction results of earthquake disasters which
were made during the ninth five-year plan; at last, the method defining the comprehensive index of cities’ ability reducing
earthquake disasters is presented. Thus the relatively comprehensive theory frame is set up. The frame can evaluate cities’
ability reducing earthquake disasters absolutely and quantitatively and consequently instruct the decision-making on reducing
cities’ earthquake disasters loss.
Foundation item: State Important Research Project of China (95130603). 相似文献
9.
Robert Tenzer Pavel Novák Ilya Prutkin Artu Ellmann Peter Vajda 《Studia Geophysica et Geodaetica》2009,53(2):157-167
To reduce the numerical complexity of inverse solutions to large systems of discretised integral equations in gravimetric
geoid/quasigeoid modelling, the surface domain of Green’s integrals is subdivided into the near-zone and far-zone integration
sub-domains. The inversion is performed for the near zone using regional detailed gravity data. The farzone contributions
to the gravity field quantities are estimated from an available global geopotential model using techniques for a spherical
harmonic analysis of the gravity field. For computing the far-zone contributions by means of Green’s integrals, truncation
coefficients are applied. Different forms of truncation coefficients have been derived depending on a type of integrals in
solving various geodetic boundary-value problems. In this study, we utilise Molodensky’s truncation coefficients to Green’s
integrals for computing the far-zone contributions to the disturbing potential, the gravity disturbance, and the gravity anomaly.
We also demonstrate that Molodensky’s truncation coefficients can be uniformly applied to all types of Green’s integrals used
in solving the boundaryvalue problems. The numerical example of the far-zone contributions to the gravity field quantities
is given over the area of study which comprises the Canadian Rocky Mountains. The coefficients of a global geopotential model
and a detailed digital terrain model are used as input data. 相似文献
10.
Matthieu Kretzschmar Thierry Dudok de Wit Jean Lilensten Jean-Francois Hochedez Jean Aboudarham Pierre-Olivier Amblard Frederic Auchère Said Moussaoui 《Acta Geophysica》2009,57(1):42-51
The knowledge of solar extreme and far ultraviolet (EUV) irradiance variations is essential for the characterization of the
Earth’s upper atmosphere. For a long time, this knowledge has been based on empirical models, which are themselves based on
proxies of the solar activity. However, the accurate modeling and prediction of the Earth’s upper atmosphere necessitate to
improve the precision on the irradiance and its variations below about 200 nm. Here, we present a review of recent works made
by the authors that aim at quantifying the irradiance variability at these wavelengths, and that lead to new way of monitoring
the solar EUV/FUV irradiance spectrum. In more details, it is shown that the quantification of the high level of redundancy
in the solar spectrum variability allows to envisage measuring only a small portion of the spectrum without losing essential
knowledge. Finally, we discuss what should and could be measured in order to retrieve the solar extreme and far ultraviolet
spectrum. 相似文献