Data assimilation (4D-VAR) to forecast flood in shallow-waters with sediment erosion     

Eric Blanger  Alain Vincent 《Journal of Hydrology》2005,300(1-4):114-125

In this paper, the four-dimensional variational data assimilation technique (4D-VAR) is presented as a tool to forecast floods. Our study is limited to purely hydrological flows and supposes that the weather, here a big rain, has been already forecasted by meteorological services. The technique consists in minimizing, in the sense of Lagrange, the cost function: a measure of the difference between calculated data and available observations, here the water level. This is done under constraints that are the equations of the physical model. In our case, we modified the shallow-water equations to include a simplified sediment transport model. The steepest descent algorithm is then used to find the minimum. This is made possible because we can compute analytically the gradient of the cost function by using the adjoint equations of the model. As an application of the 4D-VAR technique, the overflowing of the Chicoutimi River at the Chute-Garneau dam, during the 1996 flood, is investigated. It is found that the 4D-VAR method reduces the error in the water height forecast even when the erosion model is not activated. In terms of Lyapunov exponents, we estimate the predictability horizon of such an event to be about half-an-hour after a big rain. However, this limit of predictability can be increased by using more observations or by using a finer computational grid.  相似文献   

Editorial     

Raymond Michels  Laurence Mansuy  Marcel Elie  Pierre Faure  Vincent Huault  Luis Martinez  Jacques Pironon 《Organic Geochemistry》2002,33(12)

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Book review: L'écologie urbaine et l'urbanisme. Aux fondements des enjeux actuels     

Vincent Berdoulay  Olivier Soubeyran 《GeoJournal》2002,57(4):346-347

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Palaeomagnetism of East Siberian traps and kimberlites: two new poles and palaeogeographic reconstructions at about 360 and 250 Ma     

Vadim A. Kravchinsky  Konstantin M. Konstantinov  Vincent Courtillot  Jams I. Savrasov  Jean-Pierre Valet  Sergey D. Cherniy  Sergey G. Mishenin  Boris S. Parasotka 《Geophysical Journal International》2002,148(1):1-33

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Finite-difference modelling of two-dimensional elastic wave propagation in cracked media     

Vincent A. van Antwerpen  Wim A. Mulder  Gérard C. Herman 《Geophysical Journal International》2002,149(1):169-178

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Wet Snow Avalanche Deposits in the French Alps: Structure and Sedimentology   总被引：4，自引：0，他引：4  

Vincent Jomelli  & Pascal Bertran 《Geografiska Annaler: Series A, Physical Geography》2001,83(1-2):15-28

We analyse the morphology and sedimentology of 25 dirty snow avalanche deposits in the French Alps. The deposits typically have either a snow-ball structure or a massive structure with sliding planes. The snow balls show a longitudinal and a vertical sorting that reflects a sieve effect, similar to that observed in other rapid inertial granular flows. The massive type results from snow compaction when the avalanche is channelled by a gully or when it reaches the distal part of the scree. Velocity decrease and compaction limit the deformation to a zone at the base of the snow mass and cause the formation of distinctive sliding planes. These appear as smooth recrystallised surfaces due to local melt from frictional heating. The flow can be assimilated to a frictional granular flow. No systematic variation of size and shape of the rock debris has been observed along the profiles in both types of deposit. The distribution of rock debris and its fabric suggest that the clasts are transported passively and do not undergo any sorting during displacement. Snow melt after avalanching causes a redistribution of rock debris particularly when the snow thickness is important. This redistribution does not generate new sedimentological characteristics such as enhanced sorting or fabric.  相似文献   

The influence of the coast on the dynamics of upwelling fronts: Part II. Numerical simulations     

Pascale Bouruet-Aubertot  Vincent Echevin 《Dynamics of Atmospheres and Oceans》2002,36(1-3)

We investigated the dynamics of upwelling fronts near a coast. This work was first motivated by laboratory experiments [Bouruet-Aubertot, Linden, Dyn. Atmos. Oceans, 2002] in which the front is produced by the adjustment of a buoyant fluid initially confined within a bottomless cylinder. It was shown that cyclonic eddies consisting of coastal waters are enhanced when the front is unstable near the coast (the outer vertical boundary). The purpose of this paper is to provide further insights into this process. We reproduced the experimental configuration using a three-dimensional model of the primitive equations. We first show that for coastal fronts more potential energy, in terms of the maximum available potential energy, is released than for open-ocean fronts. Therefore, waves of larger amplitude are generated during the adjustment and the mean flow that establishes has a higher kinetic energy in the former case. Then as baroclinic instability starts and wave crests reach the boundary, cyclonic eddies are enhanced as in the laboratory experiments and in a similar way. However, in contrast to the laboratory experiments, offshore advection of cyclonic eddies can occur in two stages, depending on the spatial organization of the baroclinic wave. When the baroclinic wave consists of the sum of different modes and is thus highly asymmetric, the offshore advection of cyclonic eddies occurs just after their enhancement at the boundary, as in the laboratory experiments. By contrast, when a single-mode baroclinic wave develops, neighboring cyclonic eddies first merge before being advected offshore. Very different behavior is observed for open-ocean fronts. First a mixed baroclinic–barotropic instability grows. Then the eddies transfer their energy to the mean flow and the barotropic and baroclinic instabilities start again. An excellent agreement is obtained with the main result obtained in the laboratory experiments: the ratio between growth rates of surface cyclonic and anticyclonic vorticity increases as the instability develops nearer to the coast.  相似文献   

Multispectral thermal infrared mapping of the 1 October 1988 Kupaianaha flow field,Kilauea volcano,Hawaii     

Vincent J Realmuto  Ken Hon  Anne B Kahle  Elsa A Abbott  David C Pieri 《Bulletin of Volcanology》1992,55(1-2):33-44

Multispectral thermal infrared radiance measurements of the Kupaianaha flow field were acquired with the NASA airborne Thermal Infrared Multispectral Scanner (TIMS) on the morning of 1 October 1988. The TIMS data were used to map both the temperature and emissivity of the surface of the flow field. The temperature map depicted the underground storage and transport of lava. The presence of molten lava in a tube or tumulus resulted in surface temperatures that were at least 10° C above ambient. The temperature map also clearly defined the boundaries of hydrothermal plumes which resulted from the entry of lava into the ocean. The emissivity map revealed the boundaries between individual flow units within the Kupaianaha field. In general, the emissivity of the flows varied systematically with age but the relationship between age and emissivity was not unique. Distinct spectral anomalies, indicative of silica-rich surface materials, were mapped near fumaroles and ocean entry sites. This apparent enrichment in silica may have resulted from an acid-induced leaching of cations from the surfaces of glassy flows. Such incipient alteration may have been the cause for virtually all of the emissivity variations observed on the flow field, the spectral anomalies representing areas where the acid attack was most intense.  相似文献   

Application of the weighted residual method to diffraction by 2-D canyons of arbitrary shape: I. Incident SH waves   总被引：1，自引：0，他引：1  

Vincent W. Lee  Xiaoyun Wu 《Soil Dynamics and Earthquake Engineering》1994,13(5)

A solution for the two-dimensional scattering and diffraction of plane SH waves by canyons of arbitrary shape in an elastic half space is presented. The wave field for arbitrary geometry in this paper is computed numerically by the method of weighted residues (moment method). The wave displacement field computed by the present residual method for the case of a semi-circular canyon was shown to agree analytically and numerically with that computed by the exact closed form series solution. The same observations about ground amplifications, their dependence on frequencies and orientations of the incident waves, can be stated here for canyons of arbitrary shape as previously made for circular canyons.  相似文献   

Instantaneous velocity of mid-ocean ridges     

Vincent S. Cronin 《Tectonophysics》1994,230(3-4):151-159

Intuition suggests that all points on the same mid-ocean ridge should rotate around the relative pole of the two-plate system at the same instantaneous angular velocity. Contrary to intuition, the instantaneous angular velocity of a ridge varies from one point to another along the ridge, given the general case in which two plates move around different plate-specific poles of rotation. The variation in the instantaneous angular velocity of a ridge is a function of the motion characteristics of the plates and the position of the ridge relative to the poles of plate motion. The length or orientation of individual ridge segments is predicted to vary over time, leading to local changes in the shape of the ridge. The gradient in instantaneous angular velocity for the fast-spreading East Pacific Ridge, between the Cocos and Pacific plates, is an order of magnitude greater than the gradient along the Mid-Atlantic Ridge, between the North American and African plates. This great contrast in ridge instantaneous velocity gradients may be reflected in the contrasting ridge geometries of the East Pacific and Mid-Atlantic Ridges.  相似文献