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91.
Pressure and shear stress caused by raindrop impact at the soil surface: Scaling laws depending on the water depth
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Amina Nouhou Bako Frédéric Darboux François James Christophe Josserand Carine Lucas 《地球表面变化过程与地形》2016,41(9):1199-1210
Raindrop impact is an important process in soil erosion. Through its pressure and shear stress, raindrop impact causes a significant detachment of the soil material, making this material available for transport by sheet flow. Thanks to the accurate Navier–Stokes equations solver Gerris, we simulate the impact of a single raindrop of diameter D, at terminal velocity, on water layers of different thickness h: , , D, 2D, in order to study pressures and shear stresses involved in raindrop erosion. These complex numerical simulations help in understanding precisely the dynamics of the raindrop impact, quantifying in particular the pressure and the shear stress fields. A detailed analysis of these fields is performed and self‐similar structures are identified for the pressure and the shear stress on the soil surface. The evolution of these self‐similar structures are investigated as the aspect ratio h/D varies. We find that the pressure and the shear stress have a specific dependence on the ratio between the drop diameter and the water layer thickness, and that the scaling laws recently proposed in fluid mechanics are also applicable to raindrops, paving the road to obtain effective models of soil erosion by raindrops. In particular, we obtain a scaling law formula for the dependence of the maximum shear stress on the soil on the water depth, a quantity that is crucial for quantifying erosion materials. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
92.
Steep‐faced glaciodeltaic progradational successions are often studied in order to reconstruct the behaviour of the glacial feeder system, or changes in the sediment sink. This paper analyses the magnitude and frequency of depositional events associated with steep‐faced glacier‐fed progradational successions recorded in Scandinavia and Ireland. The successions exhibit depositional patterns that may be interpreted as a function of underlying non‐linear dynamics. A number of the sequences display fractal scaling in the frequency and thickness of foreset units. Other successions demonstrate chaotic patterns and strong relationships between delta‐front angle and bed thicknesses, suggesting that the progradation of such sequences is self‐organized, and to an extent occurs independently of forcing by the feeder system that provides sediment to the delta front. These patterns of sedimentation appear to be a function of the steepness of the delta front and/or the textural characteristics of the sediment. This paper provides further evidence for the simultaneous presence of order and chaos in Earth surface processes and calls into question the extent to which palaeoenvironmental reconstructions may be made from steep‐faced progradational successions. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
93.
Lucas Besson Chiraz Boudjabi Olivier Caumont Jacques Parent du Chatelet 《Boundary-Layer Meteorology》2012,143(1):77-95
Refractivity depends on meteorological parameters such as temperature and water vapour pressure and can be measured using
a weather radar. A realistic atmospheric simulation from the Meso-NH numerical model is used in order to describe and establish
the relation between refractivity and the dynamic and thermodynamic phenomena responsible for the development and propagation
of convection. These investigations lead to discussion of the complementarity between the refractivity and the convective
available potential energy. The relation observed between the refractivity signal and the meteorological parameters calls
the refractivity measurement into question, since it is based on phase differentiation with time and space and can be degraded
by phase aliasing problems. These aliasing problems increase with the radar frequency (perceptible in the S-band, serious
in the C-band, and more serious in the X-band) and also with the integration range and sampling time. Thus, a statistical
approach permits us to simulate the possibility of measuring the refractivity with operational radar during convective events.
A typical case in the south-east region of France is selected to simulate measurements by radar (S-band, C-band, X-band) in
convective systems, in order to evaluate the measurement feasibility, particularly in terms of phase ambiguity, related to
temporal and spatial sampling, of a future implementation of the refractivity measurement over the French operational radar
network. This numerical statistical approach is completed with a similar study using in-situ measurements performed at the
Trappes station. The seasonal and diurnal dependencies of aliasing are investigated, leading to clarification of the impact
of the turbulent fluxes on the refractivity measurement. 相似文献
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The direct precipitation of apatite in seawater is inhibited by Mg ions. The action of various factors on this precipitation is studied: addition of Ca, addition of F, reduction of pH and simultaneous effect of reduction of pH and addition either of F or of Ca. It is established that the reduction of the pH of seawater to 7 allows the precipitation of the apatite with a Ca/Mg ratio in the water of 1.2. The favourable environment for the settlement of natural apatite must then be either neutral or acid. This result is corroborated by the re-study of Gulbrandsen's equation. Such an acid environment with a high phosphorus content may be the result of oxidation of large quantities of organic matter due to previous intense biological activity. The acidity is probably brought about by bubbling of CO2. 相似文献
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97.
Silva Karita Almeida de Souza Rolim Glauco de Oliveira Aparecido Lucas Eduardo 《Theoretical and Applied Climatology》2022,148(3-4):1279-1288
Theoretical and Applied Climatology - The El Niño-Southern Oscillation (ENSO) phenomenon affects the global climate by changing temperature and precipitation patterns mainly in tropical... 相似文献
98.
da Silveira Lucas Cardoso de Oliveira Amauri Pereira Sánchez Maciel Piñero Codato Georgia Ferreira Maurício Jonas Filho Edson Pereira Marques Božnar Marija Zlata Mlakar Primož 《Boundary-Layer Meteorology》2022,185(2):197-197
Boundary-Layer Meteorology - 相似文献
99.
Michel?G.?J.?Den?ElzenEmail author Michiel?Schaeffer Paul?L.?Lucas 《Climatic change》2005,71(3):277-301
During the negotiations on the Kyoto Protocol, Brazil proposed allocating the greenhouse gas emission reductions of Annex I Parties according to the relative effect of a country’s historical emissions on global temperature increase. This paper analyses the impact of scientific uncertainties and of different options in policy implementation (policy choices) on the contribution of countries’ historical emissions to indicators of historical responsibility for climate change. The influence of policy choices was found to be at least as large as the impact of the scientific uncertainties analysed here. Building on this, the paper then proceeds to explore the implications of applying the Brazilian Proposal as a climate regime for differentiation of future commitments on the global scale combined with an income threshold for participation of the non-Annex I regions. Under stringent climate targets, such a regime leads to high emission reductions for Annex I regions by 2050, in particular for Europe and Japan. The income threshold assumptions strongly affect the Annex I reductions, even more than the impact of another burden-sharing key. A variant of the Brazilian Proposal, allocating emission reductions on the basis of cumulative emissions since 1990, would lead to a more balanced distribution of emission reductions. 相似文献
100.