Capture-zone design in an aquifer influenced by cyclic fluctuations in hydraulic gradients     

Willy Zawadzki  Don W. Chorley  Guy Patrick 《Hydrogeology Journal》2002,10(6):601-609

Design of a groundwater pumping and treatment system for a wood-treatment facility adjacent to the tidally influenced Fraser River estuary required the development of methodologies to account for cyclic variations in hydraulic gradients. Design of such systems must consider the effects of these cyclic fluctuations on the capture of dissolved-phase contaminants. When the period of the cyclic fluctuation is much less than the travel time of the dissolved contaminant from the source to the discharge point, the hydraulic-gradient variations resulting from these cycles can be ignored. Capture zones are then designed based on the average hydraulic gradient determined using filter techniques on continuous groundwater-level measurements. When the period of cyclic fluctuation in hydraulic gradient is near to or greater than the contaminant travel time, the resulting hydraulic-gradient variations cannot be ignored. In these instances, procedures are developed to account for these fluctuations in the capture-zone design. These include proper characterization of the groundwater regime, assessment of the average travel time and period of the cyclic fluctuations, and numerical techniques which allow accounting for the cyclic fluctuations in the design of the capture zone. Electronic Publication  相似文献   

On the Spatial Distribution and Seasonal Variation of Lower-Troposphere Ozone over Europe     

H. E. Scheel  H. Areskoug  H. Geiss  B. Gomiscek  K. Granby  L. Haszpra  L. Klasinc  D. Kley  T. Laurila  A. Lindskog  M. Roemer  R. Schmitt  P. Simmonds  S. Solberg  G. Toupance 《Journal of Atmospheric Chemistry》1997,28(1-3):11-28

Surface ozone data from 25 Europeanlow-altitude sites and mountain sites located between79°N and 28°N were studied. The analysiscovered the time period March 1989–February 1993.Average summer and winter O₃ concentrations inthe boundary layer over the continent gave rise togradients that were strongest in the north-west tosouth-east direction and west-east direction, respectively. WintertimeO₃ ranged from 19 to 27 ppbover the continent, compared to about 32 ppb at thewestern border, while for summer the continentalO₃ values ranged between 39 and 56 ppb and theoceanic mixing ratios were around 37 ppb. In the lowerfree troposphere average wintertime O₃ mixingratios were around 38 ppb, with only an 8 ppbdifference between 28°N and 79°N. For summerthe average O₃ levels decreased from about 55 ppbover Central Europe to 32 ppb at 79°N. Inaddition, O₃ and O_x(= O₃ + NO₂)in polluted and clean air were compared. Theamplitudes of the seasonal ozone variations increasedin the north-west to south-east direction, while thetime of the annual maximum was shifted from spring (atthe northerly sites) to late summer (at sites inAustria and Hungary), which reflected the contributionof photochemical ozone production in the lower partsof the troposphere.  相似文献   

Assessing infrequent large earthquakes using geomorphology and geodesy: the Malawi Rift     

Michael Hodge  Juliet Biggs  Katsuichiro Goda  Willy Aspinall 《Natural Hazards》2015,76(3):1781-1806

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A discontinuous finite element suspended sediment transport model for water quality assessments in river networks          下载免费PDF全文

Fabricio Fiengo Pérez  Lieve Sweeck  Marc Elskens  Willy Bauwens 《水文研究》2017,31(9):1804-1816

Suspended sediment plays an important role in the distribution and transport of many pollutants (such as radionuclides) in rivers. Pollutants may adsorb on fine suspended particles (e.g. clay) and spread according to the suspended sediment movement. Hence, the simulation of the suspended sediment mechanism is indispensable for realistic transport modelling. This paper presents and tests a simple mathematical model for predicting the suspended sediment transport in river networks. The model is based on the van Rijn suspended load formula and the advection–diffusion equation with a source or sink term that represents the erosion or deposition fluxes. The transport equation is solved numerically with the discontinuous finite element method. The model evaluation was performed in two steps, first by comparing model simulations with the measured suspended sediment concentrations in the Grote Nete–Molse Nete River in Belgium, and second by a model intercomparison with the sediment transport model NST MIKE 11. The simulations reflect the measurements with a Nash‐Sutcliffe model efficiency of 0.6, while the efficiency between the proposed model and the NST MIKE 11 simulations is 0.96. Both evaluations indicate that the proposed sediment transport model, that is sufficiently simple to be practical, is providing realistic results.  相似文献   

The Barents Sea Ice Sheet — A model of its growth and decay during the last ice maximum     

Anders Elverhi  Willy Fjeldskaar  Anders Solheim  Mona Nyland-Berg  Lars Russwurm 《Quaternary Science Reviews》1993,12(10)

On the basis of geomorphological and sedimentological data, we believe that the entire Barents Sea was covered by grounded ice during the last glacial maximum. ¹⁴C dates on shells embedded in tills suggest marine conditions in the Barents Sea as late as 22 ka BP; and models of the deglaciation history based on uplift data from the northern Norwegian coast suggest that significant parts of the Barents Sea Ice Sheet calved off as early as 15 ka BP. The growth of the ice sheet is related to glacioeustatic fall and the exposure of shallow banks in the central Barents Sea, where ice caps may develop and expand to finally coalesce with the expanding ice masses from Svalbard and Fennoscandia.The outlined model for growth and decay of the Barents Sea Ice Sheet suggests a system which developed and existed under periods of maximum climatic deterioration, and where its growth and decay were strongly related to the fall and rise of sea level.  相似文献   

Demonstration of sub-meter GPS orbit determination and 1.5 parts in 108 three-dimensional baseline accuracy     

Stephen M. Lichten  Willy I. Bertiger 《Journal of Geodesy》1989,63(2):167-189

Differential tracking of theGPS satellites in high-earth orbit provides a powerful relative positioning capability, even when a relatively small continental U.S. fiducial tracking network is used with less than one-third of the fullGPS constellation. To demonstrate this capability, we have determined baselines of up to2000 km in North America by estimating high-accuracyGPS orbits and ground receiver positions simultaneously. The2000 km baselines agree with very long baseline interferometry(VLBI) solutions at the level of1.5 parts in10 ⁸ and showrms daily repeatability of0.3–2 parts in10 ⁸. The orbits determined for the most thoroughly trackedGPS satellites are accurate to better than1 m. GPS orbit accuracy was assessed from orbit predictions, comparisons with independent data sets, and the accuracy of the continental baselines determined along with the orbits. The bestGPS orbit strategies included data arcs of at least one week, process noise models for tropospheric fluctuations, estimation ofGPS solar pressure coefficients, and combined processing ofGPS carrier phase and pseudorange data. For data arcs of two weeks, constrained process noise models forGPS dynamic parameters significantly improved the solutions.  相似文献   

A study of ozone in the Colorado mountains     

F. C. Fehsenfeld  M. J. Bollinger  S. C. Liu  D. D. Parrish  M. McFarland  M. Trainer  D. Kley  P. C. Murphy  D. L. Albritton  D. H. Lenschow 《Journal of Atmospheric Chemistry》1983,1(1):87-105

The seasonal and diurnal variations of ozone mixing ratios have been observed at Niwot Ridge. Colorado. The ozone mixing ratios have been correlated with the NO _x (NO+NO₂) mixing ratios measured concurrently at the site. The seasonal and diurnal variations in O₃ can be reasonably well understood by considering photochemistry and transport. In the winter there is no apparent systematic diurnal variation in the O₃ mixing ratio because there is little diurnal change of transport and a slow photochemistry. In the summer, the O₃ levels at the site are suppressed at night due to the presence of a nocturnal inversion layer that isolated ozone near the surface, where it is destroyed. Ozone is observed to increase in the summer during the day. The increases in ozone correlate with increasing NO _x levels, as well as with the levels of other compounds of anthropogenic origin. We interpret this correlation as in-situ or in-transit photochemical production of ozone from these precursors that are transported to our site. The levels of ozone recorded approach 100 ppbv at NO _x mixing ratios of approximately 3 ppbv. Calculations made using a simple clean tropospheric chemical model are consistent with the NO _x -related trend observed for the daytime ozone mixing ratio. However, the chemistry, which does not include nonmethane hydrocarbon photochemistry, underestimates the observed O₃ production.  相似文献   

Modelling elastic media with the wavelet transform     

João Willy Corrêa Rosa  Fabbryccio Akkazzha C. M. Cardoso  Keiiti Aki  Henrique S. Malvar  Fredy A. Villaorduña Artola  José Wilson Corrêa Rosa 《Geophysical Journal International》2001,146(2):454-488

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Geophysikalische Einflüsse auf die Länge des Sterntages     

Willy Rudloff 《Ocean Dynamics》1963,16(2):76-85

Zusammenfassung Die Änderung der Sterntaglänge schwankt im Rhythmus des Luftdruckgefälles zwischen 45 und 65° Süd sowohl im mittleren Jahresgang als auch im Ablauf der sechzig Monate der Jahre 1957–1961. Dieser überzufällige Gleichgang in Phase und Amplitude läßt sich so erklären, daß die Schwankungen der Tageslänge direkt durch den Schub oder die Bremsung der Lithosphäre, auf welche die Atmosphäre mit ihren Monsunen oder Passaten wirkt, erzeugt werden. Die den schwankenden Tropenwinden parallel gehenden außertropischen Westwinde würden voll die schiebende oder bremsende Wirkung der Tropenwinde kompensieren, wenn sie auch direkt die Lithosphäre erfaßten. Da nun aber im Gebiet der braven Westwinde die Hydrosphäre den gesamten Drehimpuls übernimmt und ihn wohl erst mit großer Verzögerung an die Lithosphäre weiterreicht, tritt die Änderung der Tageslänge auf, die sich im wesentlichen harmonisch aus einer halbjährlichen und einer jährlichen Welle zusammensetzt.

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Geophysical effects on the length of the sideral day

Summary The variations in the length of the day are found to be equal in phase to the oscillation of the atmospheric pressure gradient occurring between 45 and 65 degrees south. This rhythm manifests itself in the annual mean as well as in the course of the 60 months of the years 1957 to 1961. The rhythm that seems to be overaccidental may be explained with regard to phase and amplitude in the following way:The variations in the length of the day are produced by the pushing or braking of the lithosphere on which the atmosphere is acting by its monsoons or trade winds. The outertropical westerlies that are blowing parallel to the tropical wind would be able to compensate the pushing and braking effects if they, too, were directly acting on the lithosphere. As, however, in the region of the westerlies the hydrosphere assumes all angular momentum and apparently passes it on to the lithosphere after considerable delay, the variations in the length of the day are caused which essentially consist of the second and first harmonics.

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Effets géophysiques sur la longueur du jour sidéral

Résumé Les variations de la longueur du jour sidéral suivent le rythme du gradient de pression atmosphérique rencontré entre le 45^e et 65^e degré de latitude Sud. Elles se manifestent dans la moyenne annuelle aussi bien que dans la période des soixants mois des années de 1957 à 1961. Cette homogénéité super-aléatoire du rythme qui se montre également dans la phase et dans l'amplitude pourrait être expliquée par le fait que les variations de la longueur du jour sidéral sont directement produites par la poussée et le freinage de la lithosphère sur lequel agit l'atmosphère par ses moussons et ses vents alizés.Les vents extra-tropicaux d'ouest qui soufflent parallèlement aux vents tropicaux seraient à même de compenser les effets de la poussée et du freinage des vents tropicaux pourvu qu'ils agissent de même immédiatement sur la lithosphère. Comme, cependant, dans la région des braves vents d'ouest l'hydrosphère attire tout le moment angulaire et le passe, probablement après un long délai, au lithosphère, il se produit les variations de longueur du jour sidéral, qui se composent essentiellement d'une oscillation harmonique semestrielle et annuelle.

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Nach einem Vortrag Über Erddrehung und atmosphärische Globalzirkulation vor dem Geophysikalischen Kolloquium der Universität Hamburg am 8. Juni 1961, erweitert um die neuen Daten der Tageslänge und des Luftdruckgefälles zwischen 45° und 65° S.  相似文献   

SEM-EDX Characterisation of Tropospheric Aerosols in the Negev Desert (Israel)     

Sophie Sobanska  Cécile Coeur  Willy Maenhaut  Freddy Adams 《Journal of Atmospheric Chemistry》2003,44(3):299-322

Individual aerosol particles collected in the Negev desert in Israel during a summer and winter campaign in 1996–1997 were analysed by scanning electron microscopy with energy-dispersive X-ray analysis. Hierarchical cluster analysis was performed to interpret the data on the basis of particle diameter and composition. Eleven particle classes (groups) provided clues on sources and/or particle formation. The summer samples were enriched in sulphates and mineral dusts; the winter samples contained more sea salts, aged sea salts, and industrial particles. The fine size fraction below 1 m diameter was enriched in secondary particles and showed evidence of atmospheric processing. The secondary sulphate particles were mainly attributed to long-range transport. A regional conversion from calcite to calcium sulphate occurred during summer. Industrial particles originating from local pollution appeared during winter.  相似文献