Spatio-temporal variability of currents over a mobile dune field in the Dover Strait     

Déborah Idier  Dominique Astruc  Thierry Garlan 《Continental Shelf Research》2011,31(19-20):1955-1966

A one month field campaign featuring two spring–neap tide cycles and three strong storms has been performed in a mobile dune area located in the central part of the Dover Strait. These dunes are known to move in a complex manner as their migration direction varies in space and time (Le Bot et al., 2000, Le Bot, 2001, Le Bot and Trentesaux, 2004). In order to gain some insights into the dune motion processes we present an analysis of the spatio-temporal variability of currents in the area emphasizing the relative influence of tides and storms. A total of eight different hydro-meteorological regimes have been distinguished during the experiment duration. The analysis of the currents measurements at five locations in the area shows that the eight hydro-meteorological regimes induce very different current responses at the bottom. The residual tidal currents exhibit a significant spatial variability both in direction and in intensity. A numerical model of tidal currents over the Dover Strait confirms the strong spatio-temporal variability of the residual tidal currents featuring three singular points. Amongst them, a saddle point is located just south of the I-dune at the convergence of opposite direction residual tidal currents. The wind-induced currents are almost uniform in space, their intensity and direction however strongly depends on the wind regime and thus on time. The mean total current feature a spatial pattern which can be tidal of wind-induced currents dominated, or either in balance, depending on the regime considered. At the PERMOD campaign time scale, the total current is dominated by the residual tidal current. These results proved to give valuable insights to explain the complex dynamics of dune motion observed in this area by Le Bot et al., 2000, Le Bot, 2001, Le Bot and Trentesaux, 2004 at short and long time scales.  相似文献   

Glacial-interglacial mean sea level pressure change due to sea level, ice sheet and atmospheric mass changes     

Marie-Antoinette Mlires  Patricia Martinerie  Dominique Raynaud  Louis Lliboutry 《Global and Planetary Change》1991,3(4)

The change in the global mean atmospheric pressure between glacial and interglacial periods is evaluated at sea level. This change originates in a modification of topography and in a possible variation in the atmospheric mass. In this calculation the atmosphere is at hydrostatic equilibrium, and the parameters describing the glacial period are varied in a plausible range. The result, with constant atmospheric mass, is a mean sea level pressure decrease of 9–15 hPa linked with the deglaciation. The corresponding pressure change at the reference level corresponding to the present day sea level does not exceed one hPa. When considering only the change in the atmospheric mass, an increase which does not exceed 2 hPa is found, linked with the deglaciation.  相似文献   

The 6dF Galaxy Survey: samples, observational techniques and the first data release     

D. Heath Jones  Will Saunders  Matthew Colless  Mike A. Read  Quentin A. Parker  Fred G. Watson  Lachlan A. Campbell  Daniel Burkey  Thomas Mauch  Lesa Moore  Malcolm Hartley  Paul Cass  Dionne James  Ken Russell  Kristin Fiegert  John Dawe  John Huchra  Tom Jarrett  Ofer Lahav  John Lucey  Gary A. Mamon  Dominique Proust  Elaine M. Sadler  Ken-ichi Wakamatsu 《Monthly notices of the Royal Astronomical Society》2004,355(3):747-763

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Evolution and Morphodynamics of a Prograded Beach‐Ridge Foreland,Northern Baffin Island,Canadian Arctic Archipelago          下载免费PDF全文

Dominique St‐Hilaire‐Gravel  Donald L. Forbes  Trevor Bell 《Geografiska Annaler: Series A, Physical Geography》2015,97(3):615-631

Landward retreat (marine transgression) is a common response of coastal systems to rising relative sea level. However, given sufficient sediment supply, the coast may advance seaward. The latter response of gravel barriers has been recorded in parts of southeastern and northwestern Canada, where seaward‐rising sets of beach ridges are observed in areas of Holocene RSL rise. Cape Charles Yorke, northern Baffin Island, is a 5 km long gravel foreland characterized by seaward‐rising beach‐ridge crest elevations. The prograded morphology of the Cape Charles Yorke foreland is a prime example of coastal response to a combination of rising RSL and abundant sediment supply, an unusual and little‐documented pattern in the Canadian Arctic. The main gravel supply to Cape Charles Yorke is likely from eroding bedrock and raised marine deposits southwest of the foreland. Although not the dominant sediment source, the Cape Charles Yorke delta contributed to the formation of the foreland by sheltering it from easterly storm waves and providing an anchor point for the prograding ridges. The truncation of relict ridges by the modern shoreline suggests a recent regime shift from continuous deposition to predominant erosion. The cause and timing of this shift are unknown but could result from a recent dwindling in sediment supply, increased accommodation space, increased wave energy, and/or an accelerated rise of relative sea level.  相似文献   

Degradation assessment of LYRA after 5 years on orbit - Technology Demonstration -     

A. BenMoussa  B. Giordanengo  S. Gissot  I. E. Dammasch  M. Dominique  J.-F. Hochedez  A. Soltani  N. Bourzgui  T. Saito  U. Schühle  A. Gottwald  U. Kroth  A. R. Jones 《Experimental Astronomy》2015,39(1):29-43

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Urban Morphology Influence on Urban Albedo: A Revisit with the Solene Model     

Dominique Groleau  Patrice G. Mestayer 《Boundary-Layer Meteorology》2013,147(2):301-327

This heuristic study of the urban morphology influence on urban albedo is based on some 3,500 simulations with the Solene model. The studied configurations include square blocks in regular and staggered rows, rectangular blocks with different street widths, cross-shaped blocks, infinite street canyons and several actual districts in Marseilles, Toulouse and Nantes, France. The scanned variables are plan density, facade density, building height, layout orientation, latitude, date and time of the day. The sky-view factors of the ground and canopy surfaces are also considered. This study demonstrates the significance of the facade density, in addition to the built plan density, as the explanatory geometrical factor to characterize the urban morphology, rather than building height. On the basis of these albedo calculations the puzzling results of Kondo et al. (Boundary-Layer Meteorol 100:225–242, 2001) for the influence of building height are explained, and the plan density influence is quantitatively assessed. It is shown that the albedo relationship with plan and facade densities obtained with the regular square plot configuration may be considered as a reference for all other configurations, with the exception of the infinite street canyon that shows systematic differences for the lower plan densities. The curves representing this empirical relationship may be used as a sort of abacus for all other geometries while an approximate simple mathematical model is proposed, as well as relationships between the albedo and sky-view factors.  相似文献   

Impact of climate change on the hydrogeology of two basins in northern France     

Florence Habets  Julien Boé  Michel Déqué  Agnès Ducharne  Simon Gascoin  Ali Hachour  Eric Martin  Christian Pagé  Eric Sauquet  Laurent Terray  Dominique Thiéry  Ludovic Oudin  Pascal Viennot 《Climatic change》2013,121(4):771-785

This study presents an analysis of climate-change impacts on the water resources of two basins located in northern France, by integrating four sources of uncertainty: climate modelling, hydrological modelling, downscaling methods, and emission scenarios. The analysis focused on the evolution of the water budget, the river discharges and piezometric heads. Seven hydrological models were used, from lumped rainfall-discharge to distributed hydrogeological models, and led to quite different estimates of the water-balance components. One of the hydrological models, CLSM, was found to be unable to simulate the increased water stress and was, thus, considered as an outlier even though it gave fair results for the present day compared to observations. Although there were large differences in the results between the models, there was a marked tendency towards a decrease of the water resource in the rivers and aquifers (on average in 2050 about ?14 % and ?2.5 m, respectively), associated with global warming and a reduction in annual precipitation (on average in 2050 +2.1 K and ?3 %, respectively). The uncertainty associated to climate models was shown to clearly dominate, while the three others were about the same order of magnitude and 3–4 times lower. In terms of impact, the results found in this work are rather different from those obtained in a previous study, even though two of the hydrological models and one of the climate models were used in both studies. This emphasizes the need for a survey of the climatic-change impact on the water resource.  相似文献   

Refined conceptualization of TOPMODEL for shallow subsurface flows     

M. Todd Walter  Tammo S. Steenhuis  Vishal K. Mehta  Dominique Thongs  Mark Zion  Elliot Schneiderman 《水文研究》2002,16(10):2041-2046

The TOPMODEL framework was used to derive expressions that account for saturated and unsaturated flow through shallow soil on a hillslope. The resulting equations were the basis for a shallow‐soil TOPMODEL (STOPMODEL). The common TOPMODEL theory implicitly assumes a water table below the entire watershed and this does not conceptually apply to systems hydrologically controlled by shallow interflow of perched groundwater. STOPMODEL provides an approach for extending TOPMODEL's conceptualization to apply to shallow, interflow‐driven watersheds by using soil moisture deficit instead of water table depth as the state variable. Deriving STOPMODEL by using a hydraulic conductivity function that changes exponentially with soil moisture content results in equations that look very similar to those commonly associated with TOPMODEL. This alternative way of conceptualizing TOPMODEL makes the modelling approach available to researchers, planners, and engineers who work in areas where TOPMODEL was previously believed to be unsuited, such as the New York City Watershed in the Catskills region of New York State. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

THE WASHOUGAL METEORITE     

Dominique Y. Jrome  M. Christophe Michel-Lvy 《Meteoritics & planetary science》1972,7(4):449-462

The Washougal, Washington, U.S.A., howardite fell in 1939. We studied its mineralogy optically and determined the ranges of composition of plagioclase and pyroxenes from measurements of densities and indices of refraction. Notable among many unique xenoliths are a round object whose morphology is that of an armored chondrule; a stratified fragment; and a centimeter-sized dunite xenolith (olivine Fa_12.8). The abundances of 27 elements, including all major elements and 15 trace elements (Sc, V, Co, Ni, Cu, Ga, Sr, Y, Ba, La, Sm, Eu, Yb, Lu and Hf) are reported. To a first approximation, the composition of Washougal corresponds to a mixture of 51 weight percent of eucritic material and 49 percent of a diogenitic component, but excesses of some elements suggest a minor component of chondritic composition  相似文献   

Heliocentric evolution of the degradation of polyoxymethylene: Application to the origin of the formaldehyde (H₂CO) extended source in Comet C/1995 O1 (Hale-Bopp)     

Nicolas Fray  Yves Bénilan  Dominique Bockelée-Morvan  Jacques Crovisier 《Icarus》2006,184(1):239-254

The H₂CO production rates measured in Comet C/1995 O1 (Hale-Bopp) from radio wavelength observations [Biver, N., and 22 colleagues, 2002a. Earth Moon Planets 90, 5-14] showed a steep increase with decreasing heliocentric distance. We studied the heliocentric evolution of the degradation of polyoxymethylene (formaldehyde polymers: (CH₂O)_n, also called POM) into gaseous H₂CO. POM decomposition can indeed explain the H₂CO density profile measured in situ by Giotto spacecraft in the coma of Comet 1P/Halley, which is not compatible with direct release from the nucleus [Cottin, H., Bénilan, Y., Gazeau, M.-C., Raulin, F., 2004. Icarus 167, 397-416]. We show that the H₂CO production curve measured in Comet C/1995 O1 (Hale-Bopp) can be accurately reproduced by this mechanism with a few percents by mass of solid POM in grains. The steep heliocentric evolution is explained by the thermal degradation of POM at distances less than 3.5 AU. This study demonstrates that refractory organics present in cometary dust can significantly contribute to the composition of the gaseous coma. POM, or POM-like polymers, might be present in cometary grains. Other molecules, like CO and HNC, might also be produced by a similar process.  相似文献