Effects of the spherical terrain on gravity and the geoid   总被引：3，自引：0，他引：3  

P. Novák  P. Vaníček  Z. Martinec  M. Véronneau 《Journal of Geodesy》2001,75(9-10):491-504

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A comprehensive model inter-comparison study investigating the water budget during the BALTEX-PIDCAP period   总被引：2，自引：0，他引：2  

D. Jacob  B. J. J. M. Van den Hurk  U. Andræ  G. Elgered  C. Fortelius  L. P. Graham  S. D. Jackson  U. Karstens  Chr. Köpken  R. Lindau  R. Podzun  B. Rockel  F. Rubel  B. H. Sass  R. N. B. Smith  X. Yang 《Meteorology and Atmospheric Physics》2001,77(1-4):19-43

Summary A comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in 1995 over the Baltic Sea and its catchment area. All models were configured on a common grid using similar surface and lateral boundary conditions, and ran in either data assimilation mode (short term forecasts plus data assimilation), forecast mode (short term forecasts initialised daily with analyses) or climate mode (no re-initialisation of model interior during entire simulation period). Model results presented in this paper were generally post processed as daily averaged quantities, separate for land and sea areas when relevant. Post processed output was compared against available analyses or observations of cloud cover, precipitation, vertically integrated atmospheric specific humidity, runoff, surface radiation and near surface synoptic observations. The definition of a common grid and lateral forcing resulted in a high degree of agreement among the participating model results for most cases. Models operated in climate mode generally displayed slightly larger deviations from the observations than the data assimilation or forecast mode integration, but in all cases synoptic events were well captured. Correspondence to near surface synoptic quantities was good. Significant disagreement between model results was shown in particular for cloud cover and the radiative properties, average precipitation and runoff. Problems with choosing appropriate initial soil moisture conditions from a common initial soil moisture field resulted in a wide range of evaporation and sensible heat flux values during the first few weeks of the simulations, but better agreement was shown at later times. Received September 8, 2000 Revised April 3, 2001  相似文献   

Shear-zone controlled basins in the Blouberg area, Northern Province, South Africa: syn- and post-tectonic sedimentation relating to ca. 2.0 Ga reactivation of the Limpopo Belt     

A.J Bumby  P.G Eriksson  R Van Der Merwe  J.J Brümmer 《Journal of African Earth Sciences》2001,33(3-4)

The extent of the deposition and of the preservation of the Blouberg Formation and Waterberg Group was at least partially controlled by brittle reactivation along the Palala Shear Zone. The Palala Shear Zone in the Blouberg area (Northern Province, South Africa) is characterised by granulite-grade gneiss, and formed by sinistral transpressional collision between the Southern Marginal Zone (Kaapvaal Craton) and the Central Zone of the Limpopo Belt. The Limpopo collision is thought to have occurred either at 2.0 Ga or at 2.7 Ga with reactivation at 2.0 Ga. Deposition of the Blouberg Formation was characterised by syn-sedimentary tectonism, which is reflected by a sudden upward coarsening in sedimentary rocks, and by the presence of a strongly folded and thrusted lower member. Bedding orientations and slickenside lineation orientations suggest that vergence was towards the south, and such a tectonism can be inferred to have produced a highland area to the north, bound on the southern margin by the southern strand of the Melinda Fault. The presence of an inferred northerly upland area is supported by palaeocurrent directions and the preservational extent of the Setlaole and Makgabeng Formations of the Waterberg Group (post-Blouberg Formation). The extent and stratigraphy of the overlying Mogalakwena Formation suggests that these strata onlapped northwards over the denuding highlands. Younger Sibasa basalts of the Soutpansberg Group have been dated at ca. 1.85 Ga. Blouberg and Waterberg strata can therefore be interpreted as syn- and post-tectonic sedimentary rocks, respectively, following a ca. 2.0 reactivation event along the Palala Shear Zone. It is difficult to reconcile the succession of geological events at Blouberg with a ca. 2.0 Ga Limpopo orogeny, and thus sedimentary strata in the study area support a 2.7 Ga date for Limpopo collision, with syn-Blouberg tectonism relating to ca. 2.0 reactivation within the previously assembled Limpopo Belt.  相似文献   

Copper, cadmium and zinc in liver, kidney and muscle tissues of bottlenose dolphins (Tursiops truncatus) stranded in Florida     

Catherine M. Wood  Edward S. Van Vleet 《Marine pollution bulletin》1996,32(12):886-889

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Simulation of acid water movement in canals   总被引：1，自引：0，他引：1  

To Van Truong  Nguyen Tat Dac  Huynh Ngoc Phienc   《Journal of Hydrology》1996,180(1-4):361-371

An attempt to tackle the problem of the propagation of acid water in canals is described, and a mathematical model to simulate the acid water movement is developed, in which the jurbanite equilibrium is found to prevail. The processes of settling owing to sedimentation, precipitation and redissolution have been considered in the modelling. Data available from Tan Thanh, in the Plain of Reeds of the Mekong Delta in Viet Nam, are used as a case study.  相似文献   

Temperature dependence of the 57Fe Mössbauer parameters in riebeckite     

A. Van Alboom  E. De Grave 《Physics and Chemistry of Minerals》1996,23(6):377-386

Mössbauer spectra for two riebeckite minerals were collected at temperatures in the range 4.2 to 500 K. The magnetic-ordering temperatures were found to be 33±1 and 31±1 K respectively. Fitting the paramagnetic spectra with a discrete number of doublets (three or four) did not lead to consistent results. Instead, a superposition of an Fe³⁺ (M2) doublet and one distributed ferrous component was found to produce adequate fits with reasonable parameter values. For both samples, a minor fraction of ferrous ions was observed to be present at the M4 sites and for one of the samples at the M2 sites as well. The temperature variations of the center shifts were well reproduced using the Debye model of the lattice vibrational spectrum to evaluate the second-order Doppler shift. The characteristic Mössbauer temperatures were calculated to be in the range 340–390 K for Fe²⁺, and 520 K for Fe³⁺. The temperature dependences of the various ferrous quadrupole splittings could not be explained in terms of the point-charge model and assuming a temperature-independent energy-level scheme for the ⁵D term. It is suggested that a gradual change with temperature of the orbital-level splittings takes place. All calculations yielded a positive sign for the principal component of the electric field gradient (EFG). The spectrum recorded at 4.2 K for one of the riebeckites was fitted with a superposition of an Fe³⁺ and a Fe²⁺ hyperfine-field distribution, the latter one primarily characterizing the Fe²⁺ (M1) cations. The following relevant hyperfine data were calculated: H _hf=161 kOe, ΔE _Q=3.11 mm/s, and V _zz<0, all referring to the maximum-propability values. For the second riebeckite at 4.2 K, an additional distributed ferrous component could independently be resolved. The two maximum-probability hyperfine fields were found to be 189 and 98 kOe and the corresponding ΔE _Q values 3.10 and 2.67 mm/s. Both components exhibit a negative V _zz. The subspectra were attributed to M1 and M3 sites respectively. The Fe³⁺ hyperfine fields are 548+-2 kOe for both riebeckites. The different values found for the Fe³⁺ quadrupole shift 2?_Q for the two samples is explained by a different angle between the hyperfine field and the EFG's principal axis. The magnetic spectra recorded at 15 K and higher, could not be reproduced adequately with reasonable parameter values.  相似文献   

Carbon sources in arc volcanism, with implications for the carbon cycle   总被引：1，自引：0，他引：1  

J.C. Varekamp  R. Kreulen  R.P.E. Poorter  M.J. Van  Bergen 《地学学报》1992,4(3):363-373

New CO₂/³ He data from the East Sunda Arc (Indonesia) confirm earlier observations that arc volcanic gases have higher CO₂/³ He ratios than MOR environments.On average, > 80% of arc volcanic CO₂ is recycled, exogene carbon. Addition of a few percent of carbonate-bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases, but can not explain the He isotope observations. The CO₂/³He in arc volcanoes is not strongly dependent on the composition of modem trough sediments (e.g. deep sea clays vs carbonate-rich sequences), and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of, arcs. The sum of globally deep-subducted sediment and slab carbon exceeds the estimated arc CO₂ flux, and approximately 3.5 teramole of carbon may return annually to the mantle in convergent zones. The modem combined processes of MOR volcanism, slab alteration, and subduction volcanism do not produce a substantial carbon flux into the exosphere, and rate-changes in ocean floor spreading are unlikely to cause major changes in atmospheric CO₂ as a result of changes in the volcanic CO₂ fluxes. Intense pulses of flood basalt volcanism, however, may alter the CO₂ contents of the atmosphere over the course of a millenium or so, and influence global climate.  相似文献   

Crack propagation in sandstone: Combined experimental and numerical approach     

E. Schlangen  J. G. M. Van Mier 《Rock Mechanics and Rock Engineering》1995,28(2):93-110

Summary A combined experimental and numerical approach is adopted to investigate crack propagation in sandstone. Experiments on two types of sandstones show a simular behaviour as found in tests on concrete specimens. The heterogeneity of the material in combination with the stress situation, as a result of the applied load, governs the direction of crack propagation. Cracks that develop are not continuous, but overlaps exist mainly around the grain particles in the material. A simple lattice model, in which the material is schematized as a network of small beams, is adopted to simulate the experiments. Using the simulations carried out with the lattice model, the control parameter for stable displacement controlled four-point-shear tests was determined. The crack patterns obtained with the model are in good agreement with the experimental observations. However further study is needed to predict the load-displacement response correctly.  相似文献   

A ten-to-twelve year variation in the stratosphere of the Northern Hemisphere     

K. Labitzke  H. Van Loon 《Surveys in Geophysics》1993,14(2):187-196

This review paper for STIB (Stratosphere-Troposphere Interaction and the Biosphere; a proposed core project for IGBP) summarizes several features of a recently discovered 10–12 year oscillation in the atmosphere on the Northern Hemisphere. The oscillation is especially strong in the stratosphere during the warmer half of the year, but it is evident in the stratosphere and troposphere also in winter if the data are grouped according to the phase of the Quasi-Biennial Oscillation of the wind in the equatorial stratosphere. During the 40 years with data available to describe the oscillation it was phase locked with the 11-year solar cycle.Affiliate Scientist, NCAR.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Les bilans énergétiques approchés en variables λ, ϕ,p ett     

J. Van Mieghem 《Meteorology and Atmospheric Physics》1961,12(3):287-301

Résumé L'auteur montre comment il faut déduire les formes approchées des bilans énergétiques des mouvements atmosphériques en variables , ,p ett de leurs formes générales exactes. Il a tenu compte de la variabilité de la pression à la surface du globe.

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Summary It is shown how the approximate energy equations of atmospheric motions expressed with the independent variables , ,p andt must bederived from their exact general form. The variability of surface pressure has been taken into account.

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Zusammenfassung Es wird gezeigt, wie sich Näherungsformeln der Energiebilanzen der atmosphärischen Bewegungsvorgänge durch die unabhängigen Variablen , ,p undt von ihrer exakten Formulierung ableiten lassen; dabei wird der Veränderlichkeit des Luftdrucks an der Erdoberfläche Rechnung getragen.

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