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Spaceborne synthetic aperture radar (SAR) has been demonstrated invaluable in observing the global ocean winds and waves. SAR images acquired by multiple sensors are employed, including Sentinel-1(S-1), Envisat/ASAR, Gaofen-3 and Radarsat-2. This thesis reviews the commonly used SAR parameters (NRCS and azimuth cutoff) in the first part. A series of calibration steps are required to obtain a proper NRCS and assessment of NRCS is carried out for S-1wave mode (WV). It turns out that WV is poorly calibrated and is thus re-calibrated to obtain accurate NRCS. Azimuth cut off is demonstrated to be complementary to NRCS and can account for the sea state impact on the wind retrieval. Based on the available fully polarimetric SAR products, azimuth cut off is found to vary greatly with polarizations. The present SAR mapping transformation is sufficient to interpret the co-polarized azimuth cut off, while not for the cross-polarization. With the limitations of SAR imaging in mind, a new parameter is proposed and defined based on the SAR image cross-spectra, termed as MACS. The imaginary part of MACS is found to be a signed quantity relative to the wind direction. Given this dependence, an independent wind retrieval algorithm is expected to benefit. The magnitude of MACS is able to aid for estimate of modulation function of SAR mapping. In addition, MACS also gives promising results regarding the global wave studies. The global signatures of MACS at various wave lengths are well representative of the winds distributions, spatially and seasonally. MACS of long waves shows greater values over the storm tracks while the shorter waves are mostly within the trader winds. These results are expected to help evaluate the model outputs and complement further studies of the global wave spectral climate. Data continuity in the coming 10 years shall extend the study towards longer duration., Les radars à synthèse d'ouverture (SAR) spatioportés ont fait la preuve de leur valeur inestimable dans l'observation des vents et des vagues océaniques mondiaux. Les images SAR acquises par plusieurs capteurs sont utilisées, notamment Sentinel-1 (S-1), Envisat/ASAR, Gaofen-3 et Radarsat-2. Cette thèse passe en revue les paramètres SAR couramment utilisés dans la première partie. Une série d'étapes d'étalonnage sont nécessaires pour obtenir un NRCS approprié et une évaluation du NRCS est effectuée pour le mode d'onde S-1 (WV). Il s'avère que WV est mal calibré et est donc recalibré pour obtenir un NRCS précis. Il a été démontré que la coupure de l'azimut est complémentaire du NRCS et peut expliquer l'impact de l'état de la mer sur l'extraction du vent. D'après les produits SAR entièrement polarimétriques disponibles, la coupure de l'azimut varie considérablement en fonction des polarisations. La transformation actuelle de la cartographie SAR est suffisante pour interpréter la coupure azimutale copolarisée, mais pas pour la polarisation croisée. Compte tenu des limites de l'imagerie SAR, un nouveau paramètre est proposé et défini en fonction du spectre croisé de l'image SAR, appelé MACS. La partie imaginaire de MACS est une quantité signée par rapport à la direction du vent. Compte tenu de cette dépendance, on s'attend à ce qu'un algorithme indépendant de récupération du vent en bénéficie. L'ampleur du MACS peut aider à estimer la fonction de modulation de la cartographie SAR. De plus, la MACS donne également des résultats prometteurs en ce qui concerne les études globales sur les vagues. Les signatures globales du MACS à différentes longueurs d'onde sont bien représentatives de la distribution spatiale et saisonnière des vents. Les MACS des vagues longues montrent des valeurs plus élevées sur les trajectoires des tempêtes alors que les vagues plus courtes sont principalement dans les vents des trader. Ces résultats devraient aider à évaluer les résultats du modèle et compléter les études ultérieures sur le climat spectral global des vagues.

Image satellite du Liban

Sea ice, which covers most of the ocean near the poles, is a key component of the climate system. Global warming is driving its massive melting, especially in the Arctic. Where sea ice cover decreases, fetch increases leading to more energetic sea states. This means potentially enhanced wavesice interactions effects in the future. The quick evolution of sea ice extent and volume combined with the intensification of human activities in polar regions urge us to improve our understanding of waves-ice interactions.Sea ice attenuates waves. They can however propagate through it and break it far into the ice cover. Attenuation depends on ice properties such as floe size, thickness, etc. Once broken, resulting floes are more likely to drift and melt. In addition, wave attenuation yields a force which pushes the floes in the direction of wave propagation.A simplified representation of sea ice, including a floe size distribution, has been incorporated in a wave model.It allows us to show the important contribution of dissipative mechanisms in the wave attenuation, especially those induced by the bending of the ice plates. After validation, the modified wave model is coupled to an ice model. The floe size distribution is exchanged in the coupled framework and used in ice lateral melt computation. The force exerted by the waves on the ice floes is sent from the wave model and is shown to compact sea ice in summer. This reduces the melting and significantly increases the temperature and salinity in the surface ocean close to the ice edge., La banquise, qui couvre de larges étendues de l’océan près des pôles, est une composante majeure du climat. Le réchauffement de la planète entraîne sa fonte massive, en particulier en Arctique.Là où l’extension de la banquise diminue, l’augmentation du fetch est associée à une élévation de la hauteur des vagues, laissant penser que les effets liés aux interactions vagues-glace pourraient s’accroître dans le futur. L’évolution rapide de la banquise associée à l’intensification des activités humaines dans les régions polaires pressent à améliorer notre connaissance de ces interactions.La banquise atténue les vagues. Elles peuvent néanmoins s’y propager et briser la glace sur de longues distances. L’atténuation dépend des propriétés de la glace comme l’épaisseur, la taille des plaques... Les plaques de glace une fois cassées sont plus susceptibles de dériver et de fondre. En outre, lors de l’atténuation, les plaques sont poussées dans la direction de propagation des vagues.Une représentation simple de la banquise dans un modèle de vagues intégrant une distribution de la taille des plaques nous a permis de montrer l’importance des mécanismes dissipatifs dans l’atténuation, notamment ceux induits par la flexion de la glace.Après avoir été validé, ce modèle a été couplé à un modèle de glace. La taille des plaques est échangée et utilisée dans le calcul de la fonte latérale. La force exercée par les vagues sur la banquise est également envoyée depuis le modèle de vagues. En été, cette force compacte la glace et tend à diminuer la fonte, augmentant significativement la température et la salinité des eaux de surface au bord de la banquise.

In this paper, a Least Squares Support Vector Machine (LS-SVM), as a modern approach to data analysis and modelling using the methods and tools of artificial intelligence, was employed to model and predict the temperature and relative humidity as the prime climatic parameters for the development and growth of the crop under a greenhouse. In the development of LS-SVM models, linear kernel, polynomial kernel and Gaussian radial basis function (RBF were applied to train the LS-SVM. For that, external climate variables and command inputs were considered as input variables to the model to get the estimated greenhouse temperature and relative humidity. The performances of the LS-SVM models, computed through the Root Mean Square Error (RMSE) and determination coefficient. The proper LS-SVM tuning parameters, the regularization parameter �� and the kernel function parameter �� were adjusted to get the best LSSVM outputs. The simulation results showed that RBF kernel boasted better precision and generalization than linear and polynomial kernels and thus able to provide precision for the relevant greenhouse climate parameters estimation., REVUE DE L���ENTREPRENEURIAT ET DE L���INNOVATION, Vol. 2, No 6 (2018)

International audience; In this paper, we deal with a frequency modulated continuous wave (FMCW) radar used for localizing and tracking targets by frequency evaluation of the received radar beat signal. We consider the transponder as target and we achieve an identification application through frequency identification thanks to the shift frequency induced by the active target. The localization performance of FMCW radars based on radio-identification in the range (SHF) are presented and studied. Simulations and measurements complete the paper.; Dans cet article, nous traitons d'un système radar à onde continue à modulation de fréquence (FMCW) utilisé pour localiser et suivre des cibles par l'évaluation de la fréquence du signal de battement radar reçu. Nous considérons un transpondeur linéaire comme cible et nous réalisons une identification de cible grâce à la fréquence de décalage induite par cette cible active. Les performances de localisation des radars FMCW basés sur la radio-identification dans la gamme (SHF) sont présentées et étudiées. Des simulations et des mesures viennent compléter le papier.

Air temperature is one of the most important variables of high altitude mountain climate, however it is often difficult to measure it because of the shortage of active weather stations. In order to estimate this variable locally and accurately, it may be useful to refer to data from the lowest altitude weather stations and to apply the local vertical thermal gradient. From semi-hourly or hourly temperatures, monthly and seasonal vertical thermal gradients were calculated. In all cases, we obtained different values from the standard thermal gradient: they oscillate on average between -1.2 ° C / 100 m and 1.9 ° C / 100 m. The average monthly and seasonal values vary considerably between the pairs of stations studied. A better knowledge of the temperature of high altitude zones allows the realization of models of spatial distribution of temperatures at fine scales, which are crucial for scientific research.

International audience; Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age-scale uncertainty are essential to interpret the climate and environmental records that they contain. It is, however, a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inference of three quantities: the surface accumulation rate, the lock-in depth (LID) of air bubbles and the thinning function. The chronological information integrated into IceChrono1 are modeling scenarios of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice-and air-dated horizons, ice and air depth intervals with known durations, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air) and finally ice, air or mix stratigraphic links in between ice cores. the inference problem is formulated as a least squares optimisation, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg-Marquardt algorithm (thus assuming that the model is almost linear in the vicinity of the solution) and a numerical evaluation of the model's Jacobian. IceChrono1 is freely available under the General Public License v3 open source license.; Les forages polaires fournissent des archives exceptionnelles des conditions climatiques et environnementales passées. Produire une datation robuste des carottes de glace ainsi qu'une estimation de l'incertitude associée est essentiel pour interpréter les enregistrements climatiques et environnementaux qu'elles contiennent. Cependant, c'est une tâche complexe car elle implique d'utiliser différentes méthodes. Dans cet article, nous présentons IceChrono1, un modèle probabiliste qui combine différentes sources d'information chronologique pour produire une datation commune et optimale pour plusieurs carottes de glace, ainsi qu'une estimation de l'incertitude associée. IceChrono1 est basé sur l'inférence de trois quantités : le taux d'accumulation de neige en surface, la profondeur de piégeage de l'air et la fonction d'amincissement. IceChrono1 intègre de multiples informations chronologiques : un scénario modélisé du processus de sédimentation (accumulation de la neige, densification de la neige en glace et piégeage de l'air, écoulement de la glace), des horizons bien datés pour contraindre l'âge de la glace ou l'âge de l'air, des intervalles de profon-deur définis sur la glace ou via des mesures sur l'air piégé dont la durée est connue, des observations du Δprofondeur (le décalage en profondeur entre des événements synchrones enregistrés dans la glace et dans l'air) et finalement des liens stratigraphiques reliant des marqueurs identifiés dans la glace, dans l'air piégé ou dans les deux à la fois entre les carottes de glace. L'inférence est formulée comme un problème d'optimisation aux moindres carrés, impliquant que toutes les densités de probabilités sont supposées gaussiennes. Elle est résolue numériquement en utilisant l'algorithme de Levenberg-Marquardt (supposant ainsi que le modèle est presque linéaire au voisinage de la solution) et une évaluation numérique du Jacobien du modèle. IceChrono1 est librement disponible sous la licence libre GPL v3 (General Public License v3).

13ème colloque inter-universitaire Franco-Québécois sur la thermique des systèmes, Saint-Lô, FRA, 22-/05/2017 - 24/05/2017; International audience; The use of a water spray permits the evaporative cooling with the water droplet evaporation. The study of a two-phase flow is really complex due to a lot of parameters influencing the current of the droplets (flow velocity, temperature, relative humidity, characteristics of the droplets…). There are also numerous physical phenomenons which play an important role: evaporation, dispersion, sedimentation, collision, deposit… This paper presents the development of an Eulerian model simulating the injection of water droplets in an air flow. This model is based on the use of three thermodynamical variables: the liquid potential temperature, the sum of specific humidity for vapor and water droplets, and the number of droplets. The droplet evaporation is developed in the model and coupled with a Gaussian model to represent droplet dispersion. Results are first presented, then are compared to experimental measurements. Good similarities are observed on the air cooling. Moreover, parametric analyses are performed in order to gain insight into the impact of some parameters (relative humidity, water mass flow rate, droplet size).

Coexistences et transitions dans l’agriculture [Introduction]

International audience; In the data mining community, unsupervised classification (or clustering) technics are used to reveal and explore the hidden structure of a dataset. Among them, mixture models and in particular Gaussian Mixture Models (GMM), are a very popular tool. With GMM, the statistical distribution of the dataset is decomposed into a weighted sum of Gaussian modes that maximizes the likelihood of the dataset. Multivariate Gaussian distributions characterize a mode in the D-dimensional space of the dataset. This technic is routinely used in atmospheric science to describe weather regimes but is yet to be explored in physical oceanography. Here, we are interested in determining the structure of the North Atlantic ocean temperature field. Argo profiles in the North atlantic were compressed along their vertical axis in order to reduce the dimensionality of the problem. We then fitted GMMs to this reduced profile dataset according to a Maximum Likelihood criterion using the Expectation-Maximization algorithm. A seven-mode GMM was the most relevant to describe the dataset. Each mode or cluster is characterized by the parameters of a Gaussian distribution (a mean and a covariance matrix). GMM also provides for each profile of the dataset the probability it belongs to a specific cluster. We will show that these informations can be used to describe physically coherent heat reservoirs and their variability. Indeed, we found that clusters capture the large scale climatological structure of the temperature field. Each of the cluster correspond to physically coherent regions, namely the equatorial, tropical, subtropical, intergyre and subpolar regions and are associated with reference profiles. A hierarchical clustering was applied to characterize the regional variability of the dataset. We will present those clusters and possible use both for scientific analysis of the heat content variability in the North Atlantic and technical validation of the Argo array.

Equations fondamentales da la M.H.D -Ondes magneto-atmospheriques dans une atmosphere isothrme . -Modele a deux couches isothermes .

Wind-generated surface gravity waves are ubiquitous at the ocean surface. Their period varies between 2 and 25 seconds, with wavelength varying between a few meters to several hundreds of meters. Longer and, lower frequency surface gravity waves, called infragravity (IG) waves, are associated to these short, high frequency wind-generated waves. These infragravity waves have dominant periods comprised between 30 seconds and 10 minutes, and, when they propagate freely, with horizontal wavelengths of up to tens of kilometres, as given by the linear surface gravity wave dispersion relation. Outside of surf zones, the vertical amplitude of these infragravity waves is of the order of 1-10 cm, while the amplitude of wind-generated waves is of the order of 1-10 m.Given the length scales of the infragravity wavelengths, and despite the fact that the infragravity wave field exhibits much smaller vertical amplitudes than the high frequency wind-driven waves, the infragravity wave field will be a significant fraction the signal measured by the future Surface Water Ocean Topography satellite (SWOT) mission. This infragravity wave field will have to be characterized in order to achieve the expected precision on dynamic height measurements. It appears likely that the above mentioned precision will not be feasible for high sea states and long and steep swells. One of the aims of this thesis was to provide a first quantification of these associated uncertainties. Beyond the SWOT mission, the quantification of the IG wave field is a key problem for the understanding of several geophysical phenomena, such as the understanding of microseisms and ice shelves break up., Les vagues de surface générées par le vent, généralement appelées houle ou mer de vent, sont omniprésents à la surface de I'océan. Ils sont et ont des périodes variant entre 2 et 25 secondes et de longueur d'onde variant de quelques mètres à plusieurs centaines de mètres. Il existe aussi des ondes plus longues et, à plus basse fréquence appelés ondes infragravitaires (IG), qui sont associés aux vagues courtes, générées par le vent. Ces ondes ont des périodes dominantes comprise entre 30 secondes et 10 minutes et, quand ils se propagent librement, avec des longueurs d'ondes pouvant atteindre plusieurs dizaines de kilomètres. En dehors de la zone de surf, I'amplitude verticale de ces ondes infragravitaires est de I'ordre de 1 à 10 cm, tandis que I'amplitude des vagues courtes est de I'ordre de 1-10 m.Malgré leurs petites échelles d'amplitude, ces ondes infragravitaires peuvent avoir une importance non-négligeable dans certaines situations. Elles peuvent par exemple exciter des phénomènes de seiches dans les ports et mettre en résonance des structures en mer et des lames de glaces dansI'Arctique ou I'Antarctique. Le champ d'ondes infragravitaires constituera probablement aussi une fraction significative du signal mesuré par la future mission du satellite Surface Water Ocean Topography (SWOT). Ce champ d'onde infragravitaire devra être caractérisé pour atteindre la précision attendue sur les mesures de hauteur de mer dynamiques. Il est probable que la précision visée ci-dessus ne soit pas possible pour les forts états de mer avec de longues houles. L'un des objectifs de cette thèse était de fournir une première quantification de ces incertitudes associées.Au-delà de la mission SWOT, la quantification du champ d'ondes IG est un problème clé pour la compréhension de plusieurs autres phénomènes géophysiques tels que la compréhension des microséismes.

International audience; An adjustable canceller based on microwave interferometry is proposed for ground penetrating radar applications. This canceller, built up with a power divider and an impedance tuner, is integrated in a monostatic continuous wave (CW) radar in order to improve its measurement sensitivity. A set of measurements is performed and compared with standard CW radar measurements to demonstrate the performance of this technique.

The environmental impact of pollutants and effluents discharged into the atmosphere or the oceans has led researchers to conduct studies related to this issue. Several works have been carried out in this context in order to reduce the effect on the local environment. These types of ejections in nature are modeled as jets in the presence of a density gradient. In this study we treated the problem of inclined round turbulent buoyant jets and plumes ejected in a homogeneous or stratified fluid, at rest or in motion. The prediction of the flow behavior, i.e. the evolution of its variables, is first treated theoretically from a model whose formalism is valid in both the Boussinesq case as well as in the non-Boussinesq general case. Solving the equations governing the plumes is performed numerically using a Runge-Kutta 4th order. To validate the model, laboratory experiments are performed with round jets of air and helium for a wide range of densities. The confrontation theory-experience aims here to fix the limits of validity of the theoretical model. Keywords: Buoyant jet, plume, non-Boussinesq, laser tomography, image processing, perturbation method., Comment: 6 pages, in French, 5 figures

Statistical parameters of waves on the south Aquitaine coast have been determined by comparison of two datasets: in situ local measurements on a short duration and numerical simulation outputs from the WAVEWATCH III model over a period of 6 years and 9 months. Data and simulation results are well correlated in the case of the significant wave height, whereas in the case of the peak periods and directions , this correlation is lower. This is due respectively to the intrinsic unstable nature of and the narrow distribution of . An adjustment of simulation data on measurement is then used to give an evaluation of the wave statistics for the southern fraction of the French Atlantic coast. Eventually, the relationships between the three statistical variables are analysed in order to determine representative sea states. The classification obtained shows the predominance of swell regimes, distributed on a very narrow angular sector over wind sea regimes.

To know how trees behave under windload is important to understand the impact of a windstorm on a forest and identify strategies for limiting wind damage. In order to improve our understanding of wind-tree interaction at the landscape scale, mathematical and mechanical modelling of this interaction is essential, as performing numerous specific measurements in a heterogeneous environment is not feasible.Thus, this thesis first presents the development of an original and innovative tree motion model able to simulate large deflections occurring during storms. This model allows trees to break and has sufficient simplicity to allow simulations of forest motion containing a large number of trees. This model was then coupled to an atmospheric flow model in order to represent wind storm conditions. It has been used to simulate wind-forest interaction at landscape scale. For the first time, the dynamic creation and propagation of gaps in a forest have been simulated realistically, along with the resulting wind flow modifications. Finally, further studies have demonstrated the efficiency of our model for studying the impact of forest management practices on forest vulnerability to storms.In conclusion, this new model has allowed significant advances in forest motion modelling and in the understanding of the phenomena involved during a windstorm. This knowledge should be a good basis for defining best practices in forestry management., La connaissance de la réponse au vent des arbres est importante pour mieux comprendre l'impact d'une tempête sur un massif forestier et identifier des stratégies visant à limiter les dégâts. Pour améliorer notre compréhension de l'interaction vent-plantes à l'échelle du paysage, la modélisation mathématique et mécanique de cette interaction est indispensable, la multiplication de mesures ponctuelles dans un environnement hétérogène étant difficilement réalisable. Ainsi, cette thèse présente d'abord le développement d'un modèle original et novateur du mouvement de l'arbre permettant de simuler les grandes déflexions se produisant lors de tempêtes, et ce jusqu'à la rupture, le tout avec suffisamment de simplicité dans la simulation du mouvement de forêts contenant un grand nombre d'arbres. Ensuite, ce modèle a été couplé à un modèle d'écoulement atmosphérique pour représenter les conditions de tempêtes et a permis de simuler l'interaction vent-forêt à l'échelle du paysage. Pour la première fois, la création dynamique et l'expansion de trouées dans une forêt, avec la modification de l'écoulement du vent qui en résulte, ont été simulées de manière réaliste.La suite de ce travail a montré le potentiel de notre modèle pour étudier l'impact des pratiques de gestion forestière sur la vulnérabilité des forêts face aux tempêtes.En conclusion, ce nouveau modèle apporte des avancées significatives dans la modélisation du mouvement de forêt et dans la compréhension des phénomènes en jeu lors d'une tempête. Cette connaissance devrait être une bonne base pour la définition de meilleures pratiques de gestion des forêts.

International audience; Energy and matter fluxes between the atmosphere and the land surface are affected by hydrological states of the terrestrial land surface . We must increase our knowledge of these transfer processes to improve research on climate change. To reach these objectives, we must obtained global information on the hydrological states and properties of the land-surface. The microwave remote sensing instruments are an adequate way to provide soil moisture information at large scale. Microwave remote sensing data are linked to the soil moisture but also to the roughness, texture and the physicochemical properties of the soil. In that context, the objective of this study is to develop an integrated approach to estimate effective electromagnetic properties of soils layers using ground-penetrating radar (GPR), L-band radiometer, dielectric laboratory measurements, modelling approaches and in situ measurements of essential state variables.

National audience; The evaluation of moisture and chloride content of concrete is a crucial phase for the diagnosis of corroded structures in the context of heritage preservation. The use of non-destructive techniques (NDT) allows to carrying out an effective diagnosis. Electromagnetic waves in the microwaves frequencies are recognized as a powerful tool for moisture evaluation of dielectric materials as concrete. The goal of this study is to develop an optimal tool for the evaluation of moisture content on real structures based on electromagnetic waves at frequencies range of 1 to 3 GHz. Numerical simulations of patch antennas were done for optimal design and frequency. A comparison with measurements in air and on concrete having various moisture contents indicated good effectiveness of the developed antennas.

Colloque avec actes et comité de lecture. Internationale.; International audience; Nous souhaitons affiner la compréhension de phénomènes qui ont lieu dans une chambre de combustion, dans laquelle des gouttes de carburant sont injectées. On souhaite mieux comprendre l’influence du caractère multicomposant des carburants sur l’évaporation des gouttes et on s’intéresse particulier à l’effet de la présence d’un alcool dans le mélange liquide. Un travail expérimental est nécessaire afin de constituer une base de données utile à l’amélioration des modèles d’évaporation. Une expérience modèle pour l’étude d’écoulements diphasiques turbulents a été conçue à cet effet. Le banc expérimental permet de générer dans un canal un écoulement d’air chauffé fortement turbulent et présentant des propriétés de turbulence homogène isotrope. Un spray de gouttelettes poly-dispersées de liquide bi-composant acétone/éthanol est généré dans cet écoulement. Un large accès optique permet de suivre l’évolution de l’écoulement diphasique le long du canal, et notamment la dispersion et l’évaporation des gouttes et le mélange de la vapeur et de l’air. Une campagne expérimentale de fluorescence induite par plan laser (PLIF) a été entreprise afin de caractériser les régimes d’évaporation en fonction de la composition du mélange liquide. Les concentrations instantanées de la phase vapeur d’acétone sont extraites de cette campagne. Des résultats encourageants montrent que la présence de l’alcool accélère l’évaporation des gouttes. L’influence de paramètres de l’écoulement sera étudiée afin de mieux comprendre cet effet de l’alcool sur l’évaporation, tandis que les résultats de calculs LES (simulation aux grandes échelles) en cours seront présentés à titre de comparaison. Références : Moreau F., Bazile R. (2012) Evaporation of bi-component droplets in a heated, highly turbulent flow. Experiments in Fluids, 53:331-342. Cochet M., Bazile R., Ferret B., Cazin S. (2009) Evaporation of polydispersed droplets in a highly turbulent channel flow. Experiments in Fluids, 47:379–394.

One of the potential mechanisms at the origin of climatic variability on decadal to multidecadal timescales is the thermohaline oscillation corresponding to large-scale and low frequency basin modes that result from the interaction between long planetary waves and fast inertia-gravity waves during the adjustment process. However, most of the studies dealing with this decadal oscillation were carried out in a simplified flat bottom or reduced-gravity quasigeostrophic context. This dissertation aims to study the effect of bottom topography and mean flow on the characteristics of the gravest baroclinic basin modes of variability in a mid-latitude idealized ocean basin. To that end, we make use of a two-layer shallow water (SW) model. Different bathymetries such as a flat bottom, a mid-ocean ridge and continental slopes are studied. Getting the eigenvectors from the linearized model through linear stability analysis around a state of rest reveals that (1) the selection of these modes is set by the explicit dissipation introduced in the model, (2) the oscillation period and decay rate are weakly sensitive to the form and height of the topography. Vorticity and energy budgets are computed in order to give a rationale for the decaying role of the topography via energy conversion from the baroclinic to the barotropic mode. Indeed, the barotropic flow absent in a flat bottom, results accurately from the interaction of the flat-bottomed baroclinic motion with the topographic height. However, the energy conversion under the JEBAR effect remains weaker with respect to the frictional processes. A stationary circulation is now included through wind or thermal forcing. Temporal integrations of the nonlinear model perturbed by coherent baroclinic structures with a gaussian eddy form show the strong interaction between the vortex and the topography. This interaction implies : (1) a westward acceleration of the zonal phase speed (with respect to the classic flat-bottom result), (2) a barotropic circulation built up by the conversion of the baroclinic energy into a barotropic one, and (3) an eddy sign-dependent meridional migration, even in the absence of nonlinear advection. Moreover, the decadal basin mode strongly damped by the topography and the dissipation shows a decrease of its decay rate by the large scale stationary forcing. Its oscillation period is found to be a strong function of the meridional migration of the eastward advection by the mean flow : it is shortened (T_ 16 yrs) in the wind-forced experiment and lengthened (T_ 22 yrs) with a thermal forcing., Un des mécanismes proposés pour expliquer l’origine de la variabilité climatique sur des périodes décennales à multidécennales est une oscillation propre de la circulation océanique thermohaline. Son mécanisme s’apparente aux modes de bassin basse fréquence et grande échelle qui résultent de l’interaction entre les ondes lentes planétaires et les ondes rapides de bord au cours du processus d’ajustement du bassin. Toutefois, la plupart des études de ce prototype oscillation décennale ont été menées dans des contextes simplifiés quasi-géostrophiques, à gravité réduite ou à fond plat. On se propose dans ce travail de thèse d’étudier l’effet de la topographie du fond et de la circulation moyenne sur les caractéristiques des modes de bassin baroclines. On utilise un modèle shallow water à deux couches verticales avec surface libre. Différentes bathymétries analytiques type fond plat, dorsale médio-océanique et pentes continentales sont étudiées. L’obtention des vecteurs propres du modèle linéarisé par analyse de stabilité linéaire autour d’un état au repos révèle que (1) la sélection de ces modes à basse résolution s’établit par la dissipation explicite introduite dans le modèle, (2) la période décennale et l’amortissement du mode le moins amorti sont faiblement sensibles à la topographie. Les budgets d’énergie et de vorticité de ces modes sont calculés dans le but de rationaliser le rôle amortisseur de la topographie via la conversion d’énergie qui a lieu entre les modes barotrope et barocline. En effet, une circulation barotrope, absente à fond plat, émerge à travers l’interaction entre le mode barocline à fond plat et la topographie. Toutefois, cette conversion d’énergie sous l’effet JEBAR demeure faible comparée aux processus visqueux. En présence d’une circulation stationnaire forcée par le vent et les flux de chaleur, les intégrations temporelles du modèle nonlinéaire perturbé par des structures baroclines cohérentes type tourbillons gaussiens montrent la forte interaction entre le vortex et la topographie. Cette interaction se manisfeste par : (1) une accélération de la vitesse de phase vers l’ouest par rapport au résultat à fond plat, (2) une circulation barotrope construite par la conversion de l’énergie barocline en barotrope, et (3) un déplacement méridien de l’anomalie dépendant de son signe même en l’absence d’advection nonlinéaire. Par ailleurs, le mode majeur de variabilité barocline, fortement amorti par la topographie et la dissipation dans la configuration non forcée paraît renforcé par l’écoulement stationnaire qui diminue son taux d’amortissement. Sa période d’oscillation développe une dépendance à la migration méridienne de l’advection zonale par l’écoulement moyen : elle est raccourcie (T_ 16 ans) pour le forçage par le vent et rallongée (T_ 22 ans) pour le forçage par les flux de chaleur

Aerosol particles are ubiquitous in the Earth’s atmosphere. Although a minor constituent of the atmosphere, the aerosol particles are linked to visibility reduction, adverse health effects and heat balance of the Earth. The secondary aerosols which are formed in the atmosphere from the gaseous phase : precursor gases become particles by nucleation and condensation (Seinfeld and Pandis, 1998) represents the largest source in a number concentration of atmospheric particles. The chemical reactions can play an important role by turning high volatility gases into species with low vapor pressure and thus high saturation ratio, i.e. creating favorable conditions for particulate matter formation. In this work the CHIMERE chemical transport model is used to ameliorate our understanding of the governing processes for aerosol formation and to investigate its capability to reproduce the mass and number concentrations and temporal evolution of the aerosols particles at high altitudes (as for example Puy de Dome research station), and in particular, evaluate its capacity to simulate the formation of new particles due to nucleation. For the studied cases it was investigated the impact of : a fine resolution topographical database on the accuracy of simulation of dynamical parameters at high altitude, of the use of different emissions databases in the accuracy of gas-phase and aerosol concentration predictions, what is the most adequate nucleation parameterization scheme for simulating new particle formation at high altitude and what is the influence of the choice of the primary particle size distribution on the prediction of new particle formation. Also the ability of the different theories to reproduce the occurrence or lack of a nucleation event is evaluated., Non disponible.

In this study, we describe the dynamics of an equatorial river plume using a numerical model (NEMO). The Congo river parameters are used., Ce rapport étudie la dynamique d'un panache fluvial en zone équatoriale à partir de simulations numériques idéalisées (code NEMO). Les paramètres du fleuve Congo (2ème fleuve mondial par le débit) sont utilisés.

Strong interactions and feedbacks between surface processes and deep convection occur in the Sahel. They take place over a wide range of scales. They are found to enhance surfaceatmosphere energy exchanges during the monsoon and to generate a large variability of surface sensible and latent heat fluxes in time and space.A positive feedback is observed between this variability, or more accurately soil moisture heterogeneities, and the frequency of initiation of convective systems. This feedback operates at fine scale, on the order of a few tens of kilometres. The underlying mechanisms and their modelling are discussed.

International audience; In this paper we address the joint interpolation of missing data and estimation of ocean surface velocities from multi-resolution sea surface satellite observations. A variational assimilation model is proposed. Using synthetic simulation and real SST data, we conducted experiments to evaluate the relevance of the proposed model, in particular the relevance of the fusion of observations at different resolutions and the improvement issued from the consideration of dynamics prior in the assimilation model. Numerical and qualitative results assessed the effectiveness of the proposed methods.

National audience; This paper presents a novel, efficient scheme for the analysis of Sea Surface Temperature (SST) ocean images. We consider the estimation of the velocity fields and vorticity values from a sequence of oceanic images. The contribution of this paper lies in proposing a novel, robust and simple approach based onWeighted Ensemble Transform Kalman filter (WETKF) data assimilation technique for the analysis of real SST images, that may contain coast regions or large areas of missing data due to the cloud cover.; Colloque sur le Traitement du Signal et des Images

International audience; The use of permanent magnet synchronous machines (PMSM) for in-wheel electrical motorization of an urban hybrid vehicle has been studied in this article. Two types of winding, distributed and concentrated winding around a tooth, have been considered for the winding of the PMSM. Different electromagnetic sizes such as the resistance, the inductances, the iron losses, the PM eddy-current losses and teeth magnetic forces have been considered for the comparison of the two machines performances. The study shows the advantages of concentrated winding in comparison with the distributed winding, such as the diminution of the cogging torque, the reduction of no-load emf harmonics and the increase of the flux weakening range due to the increase of the inductance. However, it is important to notice the drawbacks of concentrated winding: the high level of PM eddy-current losses and large variation of stator teeth magnetic forces. These undesired effects are due to the harmonics of magnetic field produced by the concentrated winding.; L’utilisation de machines synchrones à aimants permanents (MSAP) pour la réalisation de moteurs intégrés dans les roues d’un véhicule hybride urbain est étudiée dans cet article en considérant deux types de bobinage (i.e., à pas diamétral et à pas dentaire, bobiné autour d’une dent). Différentes grandeurs électromagnétiques telles que la résistance, les inductances, les pertes fer, les pertes dans les aimants, les pertes Joule et les forces magnétiques sur les dents sont calculées afin de comparer les performances des deux machines. L’étude montre l’intérêt d’utiliser un bobinage à pas dentaire par rapport à un bobinage à pas diamétral : le couple de détente est réduit, le taux de distorsion harmonique de la f.é.m. à vide est plus faible, les pertes Joule sont plus faibles et le défluxage de la machine est facilité par une inductance de phase plus élevée. Il convient toutefois de noter les inconvénients du bobinage concentré tels que les pertes dans les aimants et la variation des forces magnétiques auxquelles sont soumises les dents du stator. Ces effets non désirés sont dus aux harmoniques du champ magnétique provoqués par la distribution spatiale du bobinage dentaire.

A small-size meteorological mast, BEAR (Budget of Energy for Arctic regions) has been developed as a part of a new autonomous buoy for monitoring the sea ice mass balance. BEAR complements observations of the thickness and thermodynamic properties of the ice/snow pack determined by the so-called Ice-T (Ice-Thickness) buoy, giving access to bulk fluxes and energy budget at the surface, using meteorological measurements. The BEAR mast has been tested with success during ten days in April-May 2010 at Ny Alesund, in the Svalbard archipelago (Norway) showing that meteorological data were close to measurements at the same level of the Italian Climate Change Tower (CCT) from the ISAC-CNR. A discussion is undertaken on bulk fluxes determination and uncertainties. Particularly, the strategy to systematically use different relevant fluxes parameterizations is pointed out to explore flux range uncertainty before to analyze energy budget. Net radiation, bulk fluxes and energy budget are estimated using as average 10 minutes, 24 hours and the ten days of the experiment. The observation period was very short, but we observe a spring transition when the net radiation begins to warm the surface while the very small turbulent heat flux cools the surface.

In this work, we aim at developping both a model and a numerical method adapted to the simulation of rainfall runoff on agricultural fields. The model used is a system of partial differential equations for shallow water flows : namely the system of Saint Venant. Rain and infiltration are treated as source terms and with a coupled model of infiltration. Because of the hyperbolicity and conservativity properties, we are using a finite volume scheme with the hydrostatic reconstruction. This reconstruction allows us to deal with stationary equilibria and wet/dry transitions due to rainfall events. First, a systematic comparison on analytic solutions is achieved between various numerical fluxes, two second order reconstructions (a MUSCL and a modified ENO reconstructions) and different numerical treatment of the friction term. This allows us to choose a numerical method adapted to runoff simulation. Moreover it is able to catch roll waves phenomenons. Then we are interested in the rain and infiltration treatment. Infiltration is modeled thanks to the Green Ampt model. This method is thereafter generalized to two dimensions and validated on experimental results obtained by the INRA of Orléans and the IRD. The chosen numerical method has been implemented in an C++ open-source software for rainfall runoff on agricultural fields simulations : FullSWOF_2D., L’objectif de ce travail est le développement d’un modèle et d’une méthode numérique adaptés à la simulation du ruissellement d’eau de pluie sur des surfaces agricoles. Pour cela, nous utilisons un système d’équations aux dérivées partielles pour les eaux peu profondes : le système de Saint Venant. La pluie et l’infiltration y sont pris en compte par l’ajout de termes source et le couplage avec un modèle d’infiltration. Le système étant hyperbolique et conservatif nous choisissons d’utiliser un schéma aux volumes finis avec reconstruction hydrostatique. Avec cette reconstruction nous obtenons un schéma permettant de traiter les équilibres stationnaires et les interfaces sec/mouillé dues aux événements pluvieux. Tout d’abord, nous effectuons une comparaison systématique de différents flux numériques, de différentes reconstructions d’ordre deux (MUSCL et ENO modifiées) et de différentes méthodes de traitement des frottements sur des solutions analytiques unidimensionnelles. Ces comparaisons nous permettent de choisir une méthode numérique adaptée à la simulation du ruissellement qui en outre capture les phénomènes de type roll-waves. Ensuite nous nous intéressons au traitement de la pluie et de l’infiltration à l’aide du modèle de Green-Ampt. Cette méthode généralisée en dimension deux est validée sur des résultats expérimentaux obtenus à l’INRA d’Orléans et à l’IRD. La méthode numérique choisie et validée a été implémentée dans FullSWOF_2D un logiciel libre écrit en C++ pour la simulation de ruissellement d’eau de pluie sur des surfaces agricoles.

National audience; Statistical Energy Analysis (SEA) is the most popular method intended to high frequency vibrations in structures and acoustics. Based on an energy approach, SEA is a simple application of energy balance under the diffuse field assumption. In this study, a thermodynamical approach of SEA is proposed. Considering that the exact repartition of vibrational energy on modes is not known, an appropriate definition of the structure function in SEA is introduced. Then, the related relationships of vibrational temperature and vibrational entropy are derived. Similarities and differences with classical temperature and entropy of gases are discussed. In particular, the meaning and consequences of the second principle of thermodynamics are clarified within the context of SEA.

In the mid-frequency (MF) range, the number of modes of warships is very large. Predicting power radiated by the underwater part of the shell becomes difficult with a classical modal synthesis. Statistical methods such as SEA (Statistical Energy Analysis) are also limited in their capability of modelling the structural complexity. Virtual SEA method is introduced to get benefit of both deterministic modal synthesis and SEA approaches to build a fully predictive model in the MF range. Virtual SEA analysis works on an original in-vacuo finite element model (FEM) of the warship. The structural model is identified in the MF range to a numerical SEA model of which parameters are extracted from FEM. First the dynamics of the warship structure is reduced to a statistical FRF (Frequency response function) matrix (between sets of observation nodes). The partitioning into subsystems is computed from this FRF matrix by an attractive algorithm which re-orders nodes to obtain weak coupling between subsystems. Then the FRF matrix computed between all nodes is compressed following the portioning scheme. Finally, using inverse method, the various SEA parameters of the subsystems (modal density, mass and coupling loss factors) are identified from previous compressed FRF. The parametric SEA model provided by this process encapsulates the FEM dynamics in the MF range. This SEA model is then analytically coupled to external fluid to predict the power radiated in water. At the end the virtual SEA model can predict power radiated in fluid under mechanical loading in band-frequency format.

ISI Document Delivery No.: 629YQ Times Cited: 4 Cited Reference Count: 58 Cited References: An SI, 2008, J CLIMATE, V21, P3, DOI 10.1175/2007JCLI1500.1 An S-I, 2000, GEOPHYS RES LETT, V27, P1573 An SI, 2000, J CLIMATE, V13, P2044, DOI 10.1175/1520-0442(2000)0132.0.CO;2 An SI, 2005, J CLIMATE, V18, P2617, DOI 10.1175/JCLI3433.1 An SI, 2004, J CLIMATE, V17, P2399, DOI 10.1175/1520-0442(2004)0172.0.CO;2 Annamalai H, 2007, J CLIMATE, V20, P1071, DOI 10.1175/JCL14035.1 BELMADANI A, 2010, J CLIM IN PRESS CANE MA, 1976, J MAR RES, V34, P629 Capotondi A, 2006, OCEAN MODEL, V15, P274, DOI 10.1016/j.ocemod.2006.02.004 Collins M, 2005, CLIM DYNAM, V24, P89, DOI 10.1007/s00382-004-0478-x Collins M, 2000, GEOPHYS RES LETT, V27, P3509, DOI 10.1029/2000GL011747 Delworth TL, 2006, J CLIMATE, V19, P643, DOI 10.1175/JCLI3629.1 Dewitte B, 2007, J CLIMATE, V20, P2002, DOI 10.1175/JCL14110.1 Dewitte B, 2007, J CLIMATE, V20, P1035, DOI 10.1175/JCLI4060.1 Dewitte B., 2000, Journal of Climate, V13, DOI 10.1175/1520-0442(2000)0132.0.CO;2 Dewitte B, 1996, J CLIMATE, V9, P1188, DOI 10.1175/1520-0442(1996)0092.0.CO;2 DiNezio PN, 2009, J CLIMATE, V22, P4873, DOI 10.1175/2009JCLI2982.1 Fedorov AV, 2000, SCIENCE, V288, P1997, DOI 10.1126/science.288.5473.1997 Guilyardi E, 2004, J CLIMATE, V17, P4623, DOI 10.1175/JCLI-3260.1 Guilyardi E, 2006, CLIM DYNAM, V26, P329, DOI 10.1007/s00382-005-0084-6 Guilyardi E, 2009, B AM METEOROL SOC, V90, P325, DOI 10.1175/2008BAMS2387.1 HALPERN D, 1995, J GEOPHYS RES, V100, P1525 HIRST AC, 1986, J ATMOS SCI, V43, P606, DOI 10.1175/1520-0469(1986)0432.0.CO;2 IMADA U, 2006, SOLA, V2, P164 Jin FF, 2003, GEOPHYS RES LETT, V30, DOI 10.1029/2002GL015983 Kirtman BP, 1997, J CLIMATE, V10, P1690, DOI 10.1175/1520-0442(1997)0102.0.CO;2 Kirtman BP, 2002, J CLIMATE, V15, P2301, DOI 10.1175/1520-0442(2002)0152.0.CO;2 KNUTSON TR, 1995, J CLIMATE, V8, P2181, DOI 10.1175/1520-0442(1995)0082.0.CO;2 Knutson TR, 1997, J CLIMATE, V10, P138, DOI 10.1175/1520-0442(1997)0102.0.CO;2 LARGE WG, 1994, REV GEOPHYS, V32, P363, DOI 10.1029/94RG01872 Levitus S., 1998, NOAA ATLAS NESDIS 18, V1, P346 Lin JL, 2007, GEOPHYS RES LETT, V34, DOI 10.1029/2006GL028937 Liu ZY, 2005, J CLIMATE, V18, P4684, DOI 10.1175/JCLI3579.1 Meehl GA, 2001, CLIM DYNAM, V17, P515, DOI 10.1007/PL00007929 MEEHL GA, 1993, CLIM DYNAM, V8, P117 Meehl GA, 2007, B AM METEOROL SOC, V88, P1383, DOI 10.1175/BAMS-88-9-1383 MEEHL GA, 1990, J CLIMATE, V3, P72, DOI 10.1175/1520-0442(1990)0032.0.CO;2 Meehl GA, 2006, CLIM DYNAM, V26, P549, DOI 10.1007/s00382-005-0098-0 MELLOR GL, 1982, REV GEOPHYS, V20, P851, DOI 10.1029/RG020i004p00851 Merryfield WJ, 2006, J CLIMATE, V19, P4009, DOI 10.1175/JCLI3834.1 Moon BK, 2004, GEOPHYS RES LETT, V31, DOI 10.1029/2003GL018829 Moon BK, 2007, CLIM DYNAM, V29, P101, DOI 10.1007/s00382-006-0219-4 Stockdale TN, 1998, J GEOPHYS RES-OCEANS, V103, P14325, DOI 10.1029/97JC02440 Timmermann A, 2002, GEOPHYS RES LETT, V29, DOI 10.1029/2001GL013369 Timmermann A, 1999, NATURE, V398, P694 Trenberth KE, 1997, GEOPHYS RES LETT, V24, P3057, DOI 10.1029/97GL03092 van Oldenborgh GJ, 2005, OCEAN SCI, V1, P81 VECCHI GA, 2008, EXAMINING TROPICAL P, V89 Yang HJ, 2005, GEOPHYS RES LETT, V32, DOI 10.1029/2004GL021624 Yeh SW, 2006, GEOPHYS RES LETT, V33, DOI 10.1029/2005GL025653 Yeh SW, 2007, J CLIMATE, V20, P203, DOI 10.1175/JCLI4001.1 Yeh SW, 2009, NATURE, V461, P511, DOI 10.1038/nature08316 Yukimoto S., 2001, PAP METEOROL GEOPHYS, V51, P47, DOI DOI 10.2467/MRIPAPERS.51.47 ZEBIAK SE, 1987, MON WEATHER REV, V115, P2262, DOI 10.1175/1520-0493(1987)1152.0.CO;2 Zelle H, 2005, J CLIMATE, V18, P4669, DOI 10.1175/JCLI3574.1 Zhang MH, 2006, GEOPHYS RES LETT, V33, DOI 10.1029/2006GL025942 Zhang RH, 2007, GEOPHYS RES LETT, V34, DOI 10.1029/2007GL032119 Zhang RH, 2006, GEOPHYS RES LETT, V33, DOI 10.1029/2005GL025286 Yeh, Sang-Wook Dewitte, Boris Yim, Bo Young Noh, Yign Korea Meteorological Administration Research and Development [RACS_2010-2006]; CNRS (Centre National de la Recherche Scientifique); ANR (Agence Nationale de la Recherche) This work was funded by the Korea Meteorological Administration Research and Development Program under Grant RACS_2010-2006. B. Dewitte benefited from support of the CNRS (Centre National de la Recherche Scientifique) through a STAR (Science and Technology Amicable Research) program and of the ANR (Agence Nationale de la Recherche) through the PCCC (Peru Chile Climate Change) program. 4 SPRINGER NEW YORK CLIM DYNAM; The response of El Nio and Southern Oscillation (ENSO)-like variability to global warming varies comparatively between the two different climate system models, i.e., the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) Coupled General Circulation Models (CGCMs). Here, we examine the role of the simulated upper ocean temperature structure in the different sensitivities of the simulated ENSO variability in the models based on the different level of CO(2) concentrations. In the MRI model, the sea surface temperature (SST) undergoes a rather drastic modification, namely a tendency toward a permanent El Nio-like state. This is associated with an enhanced stratification which results in greater ENSO amplitude for the MRI model. On the other hand, the ENSO simulated by GFDL model is hardly modified although the mean temperature in the near surface layer increases. In order to understand the associated mechanisms we carry out a vertical mode decomposition of the mean equatorial stratification and a simplified heat balance analysis using an intermediate tropical Pacific model tuned from the CGCM outputs. It is found that in the MRI model the increased stratification is associated with an enhancement of the zonal advective feedback and the non-linear advection. In the GFDL model, on the other hand, the thermocline variability and associated anomalous vertical advection are reduced in the eastern equatorial Pacific under global warming, which erodes the thermocline feedback and explains why the ENSO amplitude is reduced in a warmer climate in this model. It is suggested that change in stratification associated with global warming impacts the equatorial wave dynamics in a way that enhances the second baroclinic mode over the gravest one, which leads to the change in feedback processes in the CGCMs. Our results illustrate that the upper ocean vertical structure simulated in the CGCMs is a key parameter of the sensitivity of ENSO-like SST variability to global warming.

The characterization of the sea clutter spatial and statistical properties is a challenging problem for improving the detection performances of any radar system confronted with strong sea clutter perturbations. On the one hand, the use of radar scatterometry made it possible to precisely determine the behavior of the sea surface backscattering coefficient and to confirm electromagnetic models. On the other hand, the imaging of the ocean by radar has been studied extensively and has led to a mature theory of synthetic aperture radar (SAR) imaging of the ocean. Nevertheless the manipulations of SAR data are handicapped by the size of data. In order to analyze SAR data, we need a very flexible tool well adapted to these data. This paper briefly presents the inner functioning of a software (i.e. the different choices of class organization and how it is convenient to use them) based on a multilook philosophy (spectral sub bands processing) and on Octave script. Then we specify the type of operations and processings, we can perform using this software. Two examples of use are presented which show the easiness of use of this software.

International audience; This article deals with a sorption/desorption model in a hygroscopic material which is derived of the thermodynamic study of the phase equilibrium between the free water and its saturated vapor pressure. This model presents the hysteresis and cyclic variation aspects of the environment relative humidity. The sorption isotherm traduces the explanation of the equilibrium between the bound water phase in the material and the vapor pressure in the environment. This model allows expressing partial variation in the relative humidity domain under variable temperature. A good fitting is obtained with experimental results.

International audience; Measurements of glacier surface velocity have been performed on the French Alps Argentière's glacier for more than ten years. Completed by precise other measurements done during the MEGATOR experimentations, the surface velocity could be calculated on one reference point located on the glacial accumulation area. The knowledge of this particular surface velocity allows solving the ambiguity of displacement fields derived from pairs of interferometric synthetic aperture radar (SAR) images acquired by ERS-1/2 satellites. These interferograms provide the surface velocity over large areas. The obtained values are then compared with in-situ precise geodetic measurements of local surface velocities. The similar obtained results permit to validate the described process.

The large scale meridional overturning circulation in the ocean is maintained by a combination of several mechanisms. This dissertation focuses on turbulent equatorial mixing, one of the key mechanisms to balance heat forcing. The motivation for the research is observations of thin layers of well-mixed density and tracers distributed intermittently over the vertical that coincide with particular features of a larger scale pattern of equatorial jets. A large number of numerical experiments at moderately high resolution was performed in order to successfully replicate the observed equatorial dynamics, which involves both quasi-barotropic extra-equatorial jets and small vertical scale equatorial deep jets. The combination of the two systems of jets builds low-potential-vorticity niches, favouring the development of inertial instability and mixing. A very high resolution simulation was performed to study the formation of fine-scale layer structures with properties similar to those observed in the Atlantic. The creation of layers appears to be irreversible and the spatial distribution of the layers matches that of the marginal condition for inertial stability. The new appreciation gained for the importance of equatorial mixing leads one to revisit the question of the global distribution of diapycnal diffusivity coefficients, the estimation of which is often based on the breaking of internal waves, whose activity decreases with latitude. The resolution of the simulations performed for this study is not fine enough to produce a direct cascade of energy toward mixing scales but invites further investigation in that area., La circulation méridienne grande échelle des océans se maintient grâce à un équilibre subtil entre différents mécanismes. Cette thèse se focalise sur le mélange équatorial turbulent, un mécanisme clé de l'équilibre thermique global. L'étude menée a été motivée par l'observation de fines couches homogènes se superposant de façon intermittente sur la verticale. Ces couches s'insèrent dans la dynamique de plus grande échelle des jets équatoriaux. Une exploration numérique a permis d'obtenir une représentation réaliste de la dynamique équatoriale constituée de jets extra-équatoriaux et de jets équatoriaux profonds. La combinaison de ces deux systèmes de jets forme des niches de faibles valeurs de vorticité potentielle, propices à l'instabilité inertielle et au mélange. Une étude numérique de très haute résolution a recréé dans ce contexte des petites structures actives aux propriétés identiques à celles observées en Atlantique. Le phénomène s'avère irréversible et son développement amène l'écoulement de plus grande échelle à s'ajuster aux zones marginales des critères d'instabilité inertielle. Ces mélanges équatoriaux permettent d'étendre la distribution globale des coefficients de diffusivité turbulente jusqu'à l'équateur où le mélange dû au déferlement des ondes internes n'est pas actif. La résolution atteinte par les simulations numériques ne permet pas encore de conclure sur une cascade d'énergie vers les échelles du mélange mais invite à de nouvelles études vers les plus petites échelles.

National audience; Multifractal techniques are applied to the study of rainfall daily time series over France simulated by the climate model CNRM-CM3 of Meteo France in a coupled climate scenario A2 over the period 1860-2100. We quantify the scaling variability of the simulated rainfall with the help of a few relevant multifractal exponents characterizing the intermittency and multifractality of the field. These multifractal exponents are determined by the Double Trace Moment (DTM), which shows a scaling range from one day to about 16 days. The opposite trends found in the evolution of the intermittency and multifractality exponents have contradictory effects on the evolution of the extremes. However, a refined analysis shows that due to the dominant effect of intermittency increase, we may expect an effective increase of rainfall extremes for the next hundred years.

One of the consequences of the global warming is the modification of the hydrological cycle and then of the freshwater flux get by the ocean which one of its forcing. The ocean circulation, and more accurately the thermohaline circulation, is able to produce some low frequency variability. We are going to study the impact of the freshwater flux on the thermohaline circulation and mainly on the decadal to millennial variability. In the ocean, as in all dynamical systems, two paradigms coexist for the explanation of the observed variability : it can be endogenous or exogenous. Some outstanding results appear. During the study of endogenous variability in a 2D latitude-depth model, the growth mechanism and the oscillation one of a centennial mode are analyzed and theirs characteristics are described. This mode, corresponding to a salinity dominated density anomaly advected around the circulation, is feed by the positive salinity feedback on the advection in the freshwater forcing zone. A millennial oscillation cycle which appears through an infinite-period bifurcation is characterized. The bifurcation is due to higher frequency mode presence during the millennial cycle. Thus, we point out that the centennial oscillation is a precursor of millennial oscillation. During the study of the exogenous variability, the optimal perturbations of the sea surface salinity influencing the ocean circulation are performed in three models of the thermohaline circulation : a latitude-depth model, a planetary-geostrophic model and a primitive equation in global realistic configuration. these three models induce finite time growths on different time scales (respectively 67 yr, 24 yr and 10.5 yr). The physical mechanisms inducing these transient growths have been analysed. For the two first models, wa have been able to verify that it is the less damped eigenmode which control the transient growth. The optimal stochastic perturbations reveal a peak at the frequencies of these less damped (respectively 150 yr and 35 yr) eigenmodes. Moreover, by this study of the optimal perturbations, we have fixed modification bound of the ocean circulation at 0.75 Sv and at 0.03 PW., Une des conséquences du réchauffement climatique est la modification du cycle hydrologique et par conséquent du flux d'eau douce reçu par l'océan qui est l'un de ces forçages. La circulation océanique, et plus précisément la circulation thermohaline, est particulièrement susceptible de produire de la variabilité basse fréquence. Nous allons nous intéresser à l'impact du flux d'eau douce sur la circulation thermohaline et principalement sur sa variabilité décennale à millénaire. Dans l'océan, comme dans tout système dynamique, deux paradigmes coexistent pour expliquer la variabilité observée : elle peut être endogène ou exogène. Plusieurs résultats notables apparaissent. Au cours de l'étude de la variabilité endogène dans un modèle 2D latitude-profondeur, les mécanismes de croissance et d'oscillation d'un mode centenaire sont analysés et ses caractéristiques décrites. Ce mode, correspondant à l'advection d'une anomalie de densité dominée par la salinité le long de la circulation, se nourrit par la rétroaction de la salinité sur l'advection dans les zones de forçage par le flux d'eau douce. De plus, un cycle d'oscillation millénaire apparaissant à travers une bifurcation période-infinie est caractérisé. La bifurcation est due à la présence de modes de plus hautes fréquences au cours du cycle millénaire. Ainsi, nous montrons que l'oscillation centenaire est un précurseur de l'oscillation millénaire. Au cours de l'étude de la variabilité exogène, les perturbations optimales de la circulation océanique par la salinité de surface sont obtenues dans trois modèles de la circulation thermohaline : un modèle latitude-profondeur, un modèle planétaire-géostrophique et un modèle aux équations primitives en configuration globale réaliste. Ces trois modèles induisent des échelles de temps des croissances en temps fini différentes (respectivement 67 yr, 24 yr et 10.5 yr). Les mécanismes physiques entraînant ces croissances transitoires différent et ont été analysés. Pour les deux premiers modèles nous avons pu vérifier que c'est le mode linéaire le moins amorti qui contrôle la croissance transitoire. De plus, les perturbations stochastiques optimales font apparaître un pic aux fréquences de ces modes les moins amortis (respectivement 150 yr et 35 yr). En outre, par cette étude des perturbations optimales, nous avons obtenu une borne de modification de la circulation océanique `a 0.75 Sv et `a 0.03 PW.

The invention relates to a method for supply to a magnetic coupler comprising several pairs of windings, each pair being formed from a first and a second adjacent paired winding, magnetically coupled to each other by means of a core of magnetic material. The method further consists of supplying (in 34) the first winding of each pair with a supply voltage or current out of phase by an angle a with relation to the supply voltage or current for the second winding of the same pair. The absolute value of the angle a is greater than or equal to 4p/N for at least one pair of windings.

In this work, two problems linked to glacier modeling are investigated. We propose an optimisation method for studying the flow of the ice and we present a numerical study about glacier thermal phenomena. In the first chapter of this thesis, we expose the models of these two problems. On one hand, we note that the boundary conditions on the bedrock are misunderstood, which explains it is difficult to obtain an accurate simulation of the motion of the ice. Also we establish a mathematical model where the bedrock boundary conditions depend on a control parameter. The aim of this study is to minimize a cost functional describing the difference between the computed velocity at the surface and the measure done. We study the cost functional with respect to the control parameter and we detail an optimisation method to solve the optimal control problem. On the other hand, we introduce two thermodynamical model governing the temperature and the water content field. The models correspond to a Stefan problem for the temperature and a convection-diffusion equation for the water content. The second chapter deals with the numerical resolution of the optimisation problem. First, a Finite Element Method (FEM) is described to solve the partial differential equations. Then, the algorithms used for the optimal control problem are detailed. Finally, this techniques are applied on two glaciers : Griesgletcher for 2D and Storglaciaren for 3D. The third chapter deals with the numerical resolution of the temperature and the water content models. A FEM is used for each problem. Concerning the temperature problem, the Stefan problem is numerically solved and the results allow to detect a free surface between the temperated ice and the cold ice. The water content field is also simulated. Numerical results are discussed on the Storglaciaren.

We consider the resolution, by a finite-volume method, of the two-dimensional model of the shallow water equations with topography and friction. Thanks to the property of invariance per rotation of the flux of shallow water equations, we show that the study of the 2D case rises from the good resolution of the monodimensional system of the shallow water equations. The numerical implementation is carried out by a finite volume scheme of Godunov type using an Riemann approximate solver of the type HLLC which preserves the positivity height of water and which is well adapted for the treatment of the shock waves. Lastly, numercal examples on academic problems are presented as well as a real case : application of the model to the phenomenon of flood of the town of Cotonou (BENIN) by the risings of the lagoon of Cotonou.

National audience; In the emergency situations, the hydrological alert and forecast systems require more and more detailed spacetime information and reliable rain forecasts in the very short term. The current weather forecasting models or the statistical methods of radar and satellite image processing cannot fully answer these requirements : numerous parameterizations, long spin-tip and computation times or strongly nonlinear dynamics of stormy cells not taken into account. The multifractal approach, physically based on the cascade models, takes into account the hierarchy of the structures and their nonlinear interactions over a wide range of space time scales, as well as the time-space anisotropy. The advantage of this approach is that it requires only a very limited number of parameters, which moreover have a strong physical significance. We present the implementation of a procedure of multifractal rain forecast using data radar to determine the past of the cascade generator. We compare two modes of multifractal forecast, respectively stochastic and deterministic.

The air-handling units (AHUs) provide complete control of temperature and humidity in air-conditioned spaces. The models of the AHU elements are nonlinear and the controlled variables, temperature and relative humidity, coupled. This paper demonstrates that in the case of sensible heat exchange without moisture removal if the outputs of the electric coils, fluid-filled coils and steam humidifiers of an AHU are considered to be the differences between the air temperature and the humidity ratio of the outlet and the inlet, then the models may be written as the product of a static and a dynamic gain. The parameters of the discrete form of these models are experimentally identified. The dynamics of the elements and of their sensors are very similar. Therefore, the parameter identification of the elements takes into account the model of the sensor, previously identified. This grey-box approach combines theoretical modelling, parameter identification of discrete models and parameter identification of partially known models by using optimization techniques.

International audience; The interpretation of radar data would ideally require extensive and numerous observations. However, the number of observations is limited by the difficulty and the cost of acquiring ground truth and radar data. On the other hand, numerical models can provide a wide range of situations, both in inputs and in outputs. More precisely, they have to provide radiometric, polarimetric, and interferometric simulations and be applicable to various forested areas (high density, high/low moisture, inhomogeneous area, etc.) and radar configurations (low/high frequency, bistatic observation, etc.). This paper is dedicated to the presentation of the capabilities of a descriptive coherent scattering model (COSMO) applied to the electromagnetic study of the backscattering by forested areas. Improvements have been implemented in order to produce in output a radar image, which can be treated with the same polarimetric and interferometric tools as those applied to real synthetic aperture radar images. Thus, comparisons are possible. COSMO has been widely tested from P- to L- bands, over temperate and tropical forests and applied to radiometry, polarimetry, and interferometry. It appears finally as an efficient simulating tool to carry out parametric studies and to analyze how the total scattered field is built from canonical mechanisms and individual scatterer contributions.

CERN has announced to have realized the first measures of its experiment CLOUD, with the aim to determine if cosmic rays may have an influence on climate

This article is devoted to the analysis, and improvement of a finite volume scheme proposed recently for a class of non homogeneous systems. We consider those for which the corressponding Riemann problem admits a selfsimilar solution. Some important examples of such problems are Shallow Water problems with irregular topography and two phase flows. The stability analysis of the considered scheme, in the homogeneous scalar case, leads to a new formulation which has a naturel extension to non homogeneous systems. Comparative numerical experiments for Shallow Water equations with sourec term, and a two phase problem (Ransom faucet) are presented to validate the scheme., Cet article concerne l'analyse et l'application, d'un schéma proposé récemment por une classe de systèmes non homogènes. Nous considérons ceux pour lesquels le problème de Riemann correpondant admet une solution autosimilaire. Deux exemples importants de tels problèmes sont l'écoulement d'eau peu profonde au-dessus d'un fond non plat et les problèmes diphasiques. l'analyse de stabilité du schéma, dans le cas scalaire homogène, amène à une nouvelle écriture qui a une extension naturelle pour le cas non homogène. Des expériences numériques comparatives pour des équations de saint-Venant avec topographie variable, et un problème diphasique (Robinet de Ransom) sont présentés pour évaluer l'efficacité du schéma.

CERN scientists are looking for a solution to fight against climatic reheating; they want to determine first the influence of cosmic rays on environment

A finite-volume method for the one-dimensional shallow-water equations including topographic source terms is presented. Exploiting an original idea by Leroux, the system of partial-differential equations is completed by a trivial equation for the bathymetry. By applying a change of variable, the system is given a celerity-speed formulation, and linearized. As a result, an approximate Riemann solver preserving the positivity of the celerity can be constructed, permitting wetting and drying flow simulations to be performed. Finally, the simulation of numerical test cases is presented.

We investigated with a quasi-geostrophic model convection in an internally heated rapidly rotating sphere. We showed that, in the small Ekman number limit, the kinetic energy of the convective solution becomes time dependent immediately above the onset of convection (relaxation oscillations). We showed that banded structures can develop immediately above the onset in the presence of Ekman pumping. The width of these bands corresponds to a balance between Ekman pumping and bulk viscosity. Then we investigated the dynamo bifurcation. We found that decreasing (resp. increasing) the Roberts (Ekman) number for a given Ekman (Roberts) number one successively obtains supercritical bifurcations, subcritical bifurcations and isola. We showed that for a given set of parameters, metastable dynamos can exist, loosing their stability after an arbitrary long period of time. We also observed that several convective solutions can exist for the same parameter set. Among these solutions some do sustain dynamo action while others do not.; Nous avons étudié à l'aide d'un modèle quasi-géostrophique la convection dans une sphère en rotation rapide en chauffage interne uniforme. Nous avons montré que dans la limite des petits nombres d'Ekman, l'action du vent zonal est de rendre l'énergie cinétique des solutions dépendante du temps dès le seuil convectif franchi (oscillations de relaxation). Nous avons aussi identifié le rôle du pompage d'Ekman pour la formation de structures en bandes dans le profil radial du vent zonal dès le seuil. La taille de ces bandes résulte d'un équilibre entre la dissipation de volume et le pompage d'Ekman.Nous avons ensuite étudié le voisinage du seuil de la bifurcation dynamo. Nous avons déterminé que pour un nombre d'Ekman (respectivement Roberts) fixé, il est possible de passer d'une bifurcation super-critique à une bifurcation sous-critique puis à un îlot en décroissant (augmentant) le nombre de Roberts (Ekman). Nous avons également mis en évidence que pour certains régimes de paramètres il peut exister des dynamos métastables. Nous avons constaté que pour un même régime de paramètres, il peut aussi exister des solutions hydrodynamiques multiples dont certaines sont dynamo et d'autres non.

Statistical parameters of waves on the south Aquitaine coast have been determined by comparison of two datasets: in situ local measurements on a short duration and numerical simulation outputs from the WAVEWATCH III model over a period of 6 years and 9 months. Data and simulation results are well correlated in the case of the significant wave height, whereas in the case of the peak periods and directions , this correlation is lower. This is due respectively to the intrinsic unstable nature of and the narrow distribution of . An adjustment of simulation data on measurement is then used to give an evaluation of the wave statistics for the southern fraction of the French Atlantic coast. Eventually, the relationships between the three statistical variables are analysed in order to determine representative sea states. The classification obtained shows the predominance of swell regimes, distributed on a very narrow angular sector over wind sea regimes.

Le LIMA (Laboratoire International des Matériaux Antigivre) en collaboration avec le CIRA (Italian Aerospace Research Centre) a développé un logiciel simulant l'accrétion de la glace en régime sec et humide sur un objet bidimensionnel fixe. Le modèle thermodynamique de l'accrétion de glace est similaire aux modèles existants, LEWICE aux États Unis, TRAJICE en Grande Bretagne, ONERA en France ou CANICE au Canada, où les corrélations empiriques ont été remplacées par des analyses physiques. La hauteur des rugosités dépend de l'état de l'eau en surface qui peut exister sous forme d'un film, de gouttes ou de ruisselets et elle est calculée à partir de l'équation d'équilibre entre les forces de tension de surface, aérodynamique et gravitationnelle. Les masses d'eau liquide résiduelle, de ruissellement et d'arrachement sont calculées à partir de modèles analytiques basés sur la hauteur des rugosités, tandis que la nouvelle position de la surface est calculée à l'aide d'une méthode géométrique basée sur les bissectrices entre les panneaux définissants la surface. Le modèle d'accrétion a été validé pour les régimes sec et humide avec des formes de glace obtenues expérimentalement en soufflerie par Shin et Bond. Les formes de glace prédites numériquement sont similaires à celles mesurées expérimentalement et le modèle a été en mesure de générer les formes complexes de glace observées comme les cornes et les cannelures. Les particularités du modèle développé font qu'il pourrait être appliqué aux cas où les vitesses sont faibles ou élevées, ou encore pour les objets tournants par rapport au sol comme pour les pales d'éoliennes ou d'hélicoptères. AMIL (Anti-Icing Materials International Laboratory), in a joint project with CIRA (Italian Aerospace Research Center), developed software to simulate ice accretion in wet and dry regime on a fixed two-dimensional object. The ice accretion thermodynamic model is similar to existing models: LEWICE in the United States, TRAJICE in the United Kingdom, ONERA in France and CANICE in Canada, into which empirical correlations were replaced by physical analyses in the developed software. The roughness height depends on the surface water state, which can exist in the form of a film, bead or rivulet and is calculated from the equilibrium equation between the surface tension, aerodynamics and gravitational forces acting over the bead. Residual, runback and shedding water masses are calculated using analytical models based on the roughness height and the new surface position is calculated using a geometric method based on the bisection between the defining panel's surfaces. The accretion model was validated for dry and wet regimes with ice profiles obtained by Shin and Bond in wind tunnel experiments. The ice profiles numerically predicted are similar to those measured in wind tunnel and the model is able to generate the complex ice profiles observed in experiments, such as horns and grooves. The characteristics of the developed model are such that it can be applied to cases where speeds are slow or fast, or those involving object rotating with regard to the ground as blades of wind turbines or helicopters.