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71.
A two-dimensional vertically integrated ice flow model has been developed to test the importance of various processes and
concepts used for the prediction of the contribution of the Greenland ice-sheet to sea-level rise over the next 350 y (short-term
response). The mass balance is modelled by the degree-day method and the energy-balance method. The lithosphere is considered
to respond isostatically to a point load and the time evolution of the bedrock follows from a viscous asthenosphere. According
to the IPCC-IS92a scenario (with constant aerosols after 1990) the Greenland ice-sheet is likely to cause a global sea level
rise of 10.4 cm by 2100 AD. It is shown, however, that the result is sensitive to precise model formulations and that simplifications
as used in the sea-level projection in the IPCC-96 report yield less accurate results. Our model results indicate that, on
a time scale of a hundred years, including the dynamic response of the ice-sheet yields more mass loss than the fixed response
in which changes in geometry are not incorporated. It appears to be important to consider sliding, as well as the fact that
climate sensitivity increases for larger perturbations. Variations in predicted sea-level change on a time scale of hundred
years depend mostly on the initial state of the ice-sheet. On a time scale of a few hundred years, however, the variability
in the predicted melt is dominated by the variability in the climate scenarios.
Received: 21 August 1996/Accepted: 12 May 1997 相似文献
72.
Summary Using the ECMWF and NMC analyses, this study documents the composite structures of the African and of the 6–9 day waves. In spite of the fact that the two types of disturbances develop over almost the same area, i.e. Central and West Africa and the tropical Atlantic, during the same season, i.e. summer, in spite of the fact that they have almost the same East-West velocity, i.e. 7–8 degree longitude per day, the structures of the two waves are very different.At 12.5°N, the African wave has an amplitude maximum in the meridional wind component whilst the zonal wind component is almost unperturbed. On the contrary, in the 6–9 day wave, at 12.5°N and also at 12.5°S, the zonal wind component has an amplitude maximum whilst the meridional wind component is very small and there is an amplitude maximum for the meridional wind component at the equator and 20°N.With 9 Figures 相似文献
73.
J. J. de Vries 《International Journal of Earth Sciences》1997,86(2):354-371
An inherent aspect of hydrogeology is the dynamic character of groundwater flow within the more passive lithospheric medium. Prediction therefore requires insight into the spatial pattern of aquifer properties as well as the dynamic character of groundwater flow systems. Both aspects together determine hydrogeological system behaviour in space and time. The spatial characteristics of an aquifer are mainly based on geological and geomorphological structure, whereas the dynamics of the system result predominantly from climate and topography; knowledge of paleoconditions are a prerequisite for sound understanding of present systems. The integration of exploration and forecast is illustrated by two case studies. The first study focuses on an assessment of groundwater resource and their sustainable development in semi-arid Botswana. The second study concerns the impact of land and water management in the Netherlands coastal area on the groundwater regime and its future development, including the redistribution of salt and fresh groundwater on a long time scale. 相似文献
74.
Sediment origin and budget in Sepetiba Bay (Brazil) - an approach based on multielemental analysis 总被引:1,自引:0,他引:1
Sediment origin and transport were determined in a shallow 447 km2 coastal lagoon in Brazil, using the distribution of major elements in bottom and suspended sediments. Applying multivariate
analysis, the sum of normalized concentrations of Ti, Fe, and Al in sediments was selected to trace the terrigenous influence
in bottom sediments, whereas Ca, Si, and K were used as indicators of marine influence. Sepetiba Bay bottom sediments are
dominated by up to 80% terrigenous inputs. The open bay sediments are enriched in P, Mg, K, and Ca because of the intensive
water column primary production. The inner bay forms an independent circulation cell with a predominance of terrigenous sediments.
The results suggest a long residence time for particles in the bay, demonstrated by the magnitude of resuspension flux compared
to the total sediment input to the bay.
Received: 29 May 1996 · Accepted: 17 December 1996 相似文献
75.
In this paper we study the infiltration of DNAPL in a porous medium containing a single low-permeable lens. Our aim is to
determine whether or not DNAPL infiltrates into the lens. A key role is played by the capillary pressure: DNAPL cannot infiltrate
into the lens unless the capillary pressure exceeds the entry pressure of the lens. In the model this is reflected by an interface
condition, the extended capillary pressure condition. To derive analytical approximations we first consider a steady-state
DNAPL plume in a homogeneous medium. This results in an estimate of the DNAPL plume width as a function of depth, and an asymptotic
solution for small saturations. Assuming that the extent of the lens is much larger than the width of the unperturbed DNAPL
plume in the homogeneous medium, we derive an explicit criterion for DNAPL infiltration into the lens in terms of a critical
inflow rate. A numerical algorithm is presented in which the extended capillary pressure condition is incorporated. The numerical
and analytical results show good qualitative agreement.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
76.
A general correspondence principle is presented that relates any time-domain electromagnetic diffusion field to an electromagnetic wavefield in a 'corresponding' configuration. The principle applies to arbitrarily inhomogeneous and anisotropic media and arbitrary transmitters and receivers. For the correspondence between the two types of electromagnetic fields to hold, the electric conductivity in the diffusive case and the permittivity in the wavefield case should have the same spatial variation, while the permeability distributions in space in the two cases are to be identical. Essential steps in the derivation of the correspondence principle are the use of the time Laplace transformation of causal signals, taken at real, positive values of the transform parameter, the Schouten-Van der Pol theorem in the theory of the Laplace transformation, and the reliance upon Lerch's theorem of the uniqueness of the interrelation between causal field quantities and their time-Laplace-transform representations at real, positive values of the transform parameter. Correspondence is then established between the tensorial Green's functions in the two cases, where the Green's functions are the point-receiver responses (either electric or magnetic field) to point-transmitter excitations (either electric- or magnetic-current source).
Through the correspondence principle, all transient electromagnetic wavefields (where losses are neglected) have as a counterpart a transient diffusive electromagnetic field (where the electric displacement current is neglected). The interrelation yields the tool to compare quantitatively the potentialities of the two types of fields in transient electromagnetic geophysical prospecting.
Finally, a general medium-parameter scaling law for time-domain electromagnetic wavefields is presented. 相似文献
Through the correspondence principle, all transient electromagnetic wavefields (where losses are neglected) have as a counterpart a transient diffusive electromagnetic field (where the electric displacement current is neglected). The interrelation yields the tool to compare quantitatively the potentialities of the two types of fields in transient electromagnetic geophysical prospecting.
Finally, a general medium-parameter scaling law for time-domain electromagnetic wavefields is presented. 相似文献
77.
Frédérick Delay Hélène Housset-Resche Gilles Porel Ghislain de Marsily 《Mathematical Geology》1996,28(1):45-71
A new method for solving the transport equation based on the management of a large numbe of particles in a discretized 2-D domain is presented. The method uses numerical variables to represent the number of particles in a given mesh and is more complex than the 1-D problem. The first part of the paper focuses on the specific management of particles in a 2-D problem. The method also would be valid for three dimensions as long as the medium can be modeled similar to a layered system. As the particles are no longer tracked individually, the algorithm is fast and does not depend on the number of particles present. The numerical tests show that the method is nearly numerical dispersion free and permits accurate calculations even for simulations of low-concentration transport. Because each mesh is considered as a closed system between two successive time steps, it is easy to add adsorption phenomenon without any problem of numerical stability. The model is tested under conditions that are extremely demanding for its operating mode and gives a good fit to analytical solutions. The conditions in which it can be used to best advantage are discussed. 相似文献
78.
79.
Geologie en Mijnbouw - 相似文献
80.