Publications

2008

• Application d'un code de CFD atmosphérique à l'estimation du productible éolien en terrain complexe
  
  • Laporte Laurent
  , 2008. La thèse se décompose en deux parties. La première concerne l'utilisation du code de CFD atmosphérique Mercure Saturne pour estimer le potentiel éolien en terrain complexe. Une campagne de mesure a été menée par EDF pour disposer de données d'entrée et de validation. Une méthodologie a été développée utilisant des profils méso-échelle comme conditions limites du code CFD. Elle utilise la classification automatique pour réduire le nombre de simulations nécessaires au calcul du potentiel. La validation du code sur le cas connu de la colline d'Askervein, la méthodologie et les comparaisons avec les mesures sur le site complexe choisi sont présentées et discutées. La seconde partie concerne l'étude des sillages avec le code Mercure Saturne. Une méthode de représentation des efforts, exercés par les pales sur le vent, utilisant des termes sources a été implémentée. Ces derniers sont calculés par la méthode BEM. Deux comparaisons en soufflerie sont proposées pour la validation (10.70675/86b53dbazae20z45d0za04az10ef4afbdbc7)
  DOI : 10.70675/86b53dbazae20z45d0za04az10ef4afbdbc7
• Satellite data assimilation for air quality forecast
  
  • Boisgontier Hervé
  • Mallet Vivien
  • Berroir Jean-Paul
  • Bocquet Marc
  • Herlin Isabelle
  • Sportisse Bruno
  Simulation Modelling Practice and Theory, Elsevier, 2008, 16 (10), pp.1541-1545. This paper presents results from a study led prior to the launch of the EPS-MetOp satellite in October 2006. It aims at assessing the feasibility of assimilating MetOp troposphere ozone soundings within a regional chemistry-transport model, in view of improving air quality forecast in the lowest layers of the troposphere. The paper furthermore analyses the computational complexity of assimilating satellite data, and concludes on the necessity of providing grid support to satellite data assimilation. (10.1016/j.simpat.2008.01.008)
  DOI : 10.1016/j.simpat.2008.01.008
• A Multi-scale Vector Spline Method for Estimating the Fluids Motion on Satellite Images
  
  • Isambert Till
  • Berroir Jean-Paul
  • Herlin Isabelle
  , 2008, IV, pp.665-676. Satellite image sequences visualize important patterns of the atmospheric and oceanographic circulation. Assessing motion from these data thus has a strong potential for improving the performances of the forecast models. Representing a vector field by a vector spline has been proven efficient for fluid motion assessment: the vector spline formulation makes it possible to initially select the locations where the conservation equation has to be taken into account; it efficiently implements the 2nd order div-curl regularity, advocated for turbulent fluids. The scientific contribution of this article is to formulate vector splines in a multiscale scheme, with the double objective of assessing motion even in the case of large displacements and capturing the spectrum of spatial scales associated to turbulent flows. The proposed method only requires the inversion of a band matrix, which is performed by an efficient numerical scheme making the method tractable for large satellite image sequences. (10.1007/978-3-540-88693-8_49)
  DOI : 10.1007/978-3-540-88693-8_49
• A comparison study of data assimilation algorithms for ozone forecasts
  
  • Wu Lin
  • Mallet Vivien
  • Bocquet Marc
  • Sportisse Bruno
  Journal of Geophysical Research, American Geophysical Union, 2008, 113 (D20310). The Institute of Radiation Protection and Nuclear Safety (France) is planning the set-up of an automatic nuclear aerosol monitoring network over the French territory. Each of the stations will be able to automatically sample the air aerosol content and provide activity concentration measurements on several radionuclides. This should help monitor the French and neighbouring countries nuclear power plants set. It would help evaluate the impact of a radiological incident occurring at one of these nuclear facilities. This paper is devoted to the spatial design of such a network. Here, any potential network is judged on its ability to extrapolate activity concentrations measured on the network stations over the whole domain. The performance of a network is quantitatively assessed through a cost function that measures the discrepancy between the extrapolation and the true concentration fields. These true fields are obtained through the computation of a database of dispersion accidents over one year of meteorology and originating from 20 French nuclear sites. A close to optimal network is then looked for using a simulated annealing optimisation. The results emphasise the importance of the cost function in the design of a network aimed at monitoring an accidental dispersion. Several choices of norm used in the cost function are studied and give way to different designs. The influence of the number of stations is discussed. A comparison with a purely geometric approach which does not involve simulations with a chemistry-transport model is performed. (10.1029/2008JD009991)
  DOI : 10.1029/2008JD009991
• The project ChArMEx - Chemistry Aerosol Mediterranean Experiment.
  
  • Dulac François
  • Mallet Marc
  • Attié Jean-Luc
  • Athier G.
  • Bergametti Gilles
  • Borbon Agnès
  • Cammas Jean-Pierre
  • Coppola L.
  • Dubovik Oleg
  • Durand Pierre
  • Flamant Cyrille
  • Gheusi François
  • Guieu Cécile
  • Lambert Dominique
  • Liousse Catherine
  • Marchand Nicolas
  • Marie Céline
  • Peuch Vincent-Henri
  • Pin F.
  • Ravetta François
  • Sartelet Karine
  • Savelli Jean-Luc
  • Sciare Jean
  • Tanré Didier
  • Textor Christiane
  • Turquety Solène
  , 2008. ChArMEx is a new regional project on tropospheric chemistry and aerosols in the Mediterranean proposed by the French community, calling for international cooperation. ChArMEx proposes an integrated modelling and observational approach to study budgets of species, chemical and dynamical processes, intense events, trends, and impacts. The objectives include an assessment of the recent past, present and future states of the atmospheric chemistry and of related impacts on air quality, regional climate and marine biogeochemistry. The experimental strategy includes long-term monitoring, 2 years of enhanced surface observations, and summer intensive campaigns with research aircrafts and drifting balloons to study the aging of continental air masses over the basin when pollutants and desert dusts are at their maximum and likely impact the regional climate. Focus is presently put on the western basin. Synergies are built with other Mediterranean projects on the hydrological cycle (HyMEx) and marine ecosystems (MERMEX).
• Assimilation of SST Satellite Images for Estimation of Ocean Circulation Velocity
  
  • Huot Étienne
  • Herlin Isabelle
  • Korotaev Gennady K.
  , 2008, II, pp.847-850. The objective of this study is to compute the surface circulation velocity from oceanographic image sequences. Data assimilation provides a mathematical solution to combine optimally observations and models. We define a dedicated Image Model consistent with the physical knowledge of ocean dynamic. Satellite images are then assimilated into this model using a variational data assimilation scheme. This technique relies on the adjoint model definition to compute the minimum of a cost function measuring the discrepancy between model's outputs and observations. The method takes into account the physical knowledge of the ocean circulation, which is relevant for explaining images evolution and, in case of missing data due to clouds occlusion or lack of acquisitions, the estimation is still consistent with the physical evolution laws. (10.1109/IGARSS.2008.4779127)
  DOI : 10.1109/IGARSS.2008.4779127
• Ontology-based Land Degradation Assessment from Satellite Images
  
  • Tomai Eleni
  • Herlin Isabelle
  • Berroir Jean-Paul
  • Prastacos Poulicos
  , 2008, XXXVII - Part B2 - Commission II, pp.703-708. In this paper, we introduce the idea of documenting operational chains for land degradation assessment using ontologies. We believe that this will help end-users in better understanding the land degradation characteristics and evaluate the results of the assessment process. Since the application domain is wide, various operational chains for land degradation assessment and their associated documentation exist, according to different options. This parameterization causes the development of different ontologies, which, nonetheless are to a certain extent linked because of the common software components of the corresponding operational chains. We therefore propose a hierarchical structure of these ontologies; so that several requirements such as understanding of expert knowledge interconnections and application domain variety, documentation, assimilation of new expert knowledge, and reusability of software components become feasible.
• Design of a monitoring network over France in case of a radiological accidental release
  
  • Abida Rachid
  • Bocquet Marc
  • Vercauteren Nikki
  • Isnard Olivier
  Atmospheric Environment, Elsevier, 2008, 42 (21), pp.5205--5219. The Institute of Radiation Protection and Nuclear Safety (France) is planning the set-up of an automatic nuclear aerosol monitoring network over the French territory. Each of the stations will be able to automatically sample the air aerosol content and provide activity concentration measurements on several radionuclides. This should help monitor the French and neighbouring countries nuclear power plants set. It would help evaluate the impact of a radiological incident occurring at one of these nuclear facilities. This paper is devoted to the spatial design of such a network. Here, any potential network is judged on its ability to extrapolate activity concentrations measured on the network stations over the whole domain. The performance of a network is quantitatively assessed through a cost function that measures the discrepancy between the extrapolation and the true concentration fields. These true fields are obtained through the computation of a database of dispersion accidents over one year of meteorology and originating from 20 French nuclear sites. A close to optimal network is then looked for using a simulated annealing optimisation. The results emphasise the importance of the cost function in the design of a network aimed at monitoring an accidental dispersion. Several choices of norm used in the cost function are studied and give way to different designs. The influence of the number of stations is discussed. A comparison with a purely geometric approach which does not involve simulations with a chemistry-transport model is performed. (10.1016/j.atmosenv.2008.02.065)
  DOI : 10.1016/j.atmosenv.2008.02.065
• PM₁₀ data assimilation over Europe with the optimal interpolation method
  
  • Tombette M.
  • Mallet V.
  • Sportisse B.
  Atmospheric Chemistry and Physics Discussions, European Geosciences Union, 2008, 8 (3), pp.9607-9640. This paper presents experiments of PM₁₀ data assimilation with the optimal interpolation method. The observations are provided by BDQA (Base de Données sur la Qualité de l'Air), whose monitoring network covers France. Two other databases (EMEP and AirBase) are used to evaluate the improvements in the analyzed state over one month (January, 2001) and for several outputs (PM₁₀, PM_2.5 and chemical composition). Then, the method is applied in operational conditions. The results show that the assimilation of PM₁₀ observations significantly improves the one-day forecast for total mass (PM₁₀ and PM_2.5). The errors on aerosol chemical composition are not reduced and are sometimes amplified by the assimilation procedure, which shows the need for chemical data. As the observations cover a limited part of the domain (France versus Europe) and as the method used for assimilation is sequential, we focus on the horizontal and temporal impacts of assimilation in the last part of this paper. To conclude, we discuss the perspectives, especially the use of a variational method for assimilation or the investigation of the sensitivity to a few choices (e.g., the error statistics, etc.). (10.5194/acp-9-57-2009)
  DOI : 10.5194/acp-9-57-2009
• Air quality modeling: From deterministic to stochastic approaches
  
  • Mallet Vivien
  • Sportisse Bruno
  Computers & Mathematics with Applications, Elsevier, 2008, 55 (10), pp.2329--2337. The objective of this article is to investigate the topics related to uncertainties in air quality modeling. A first point is the evaluation of uncertainties for model outputs: Monte Carlo methods and sensitivity analysis are powerful methods for assessing the impact of uncertainties due to model inputs. A second point is devoted to ensemble modeling with multi-models approaches. According to the wide spread in the model outputs, using a unique model, tuned to a small set of observational data, is not relevant in this field. On the basis of ensemble simulations, improved forecasts are given by appropriate algorithms to combine the set of models. The results applied to air quality modeling at continental scale with the Polyphemus system illustrate these methods. The first estimates of uncertainties in inverse modeling experiments are also proposed. (10.1016/j.camwa.2007.11.004)
  DOI : 10.1016/j.camwa.2007.11.004
• Inverse modelling of atmospheric tracers: non-Gaussian methods and second-order sensitivity analysis
  
  • Bocquet Marc
  Nonlinear Processes in Geophysics, European Geosciences Union (EGU), 2008, 15 (1), pp.127-143. For a start, recent techniques devoted to the reconstruction of sources of an atmospheric tracer at continental scale are introduced. A first method is based on the principle of maximum entropy on the mean and is briefly reviewed here. A second approach, which has not been applied in this field yet, is based on an exact Bayesian approach, through a maximum a posteriori estimator. The methods share common grounds, and both perform equally well in practice. When specific prior hypotheses on the sources are taken into account such as positivity, or boundedness, both methods lead to purposefully devised cost-functions. These cost-functions are not necessarily quadratic because the underlying assumptions are not Gaussian. As a consequence, several mathematical tools developed in data assimilation on the basis of quadratic cost-functions in order to establish a posteriori analysis, need to be extended to this non-Gaussian framework. Concomitantly, the second-order sensitivity analysis needs to be adapted, as well as the computations of the averaging kernels of the source and the errors obtained in the reconstruction. All of these developments are applied to a real case of tracer dispersion: the European Tracer Experiment [ETEX]. Comparisons are made between a least squares cost function (similar to the so-called 4D-Var) approach and a cost-function which is not based on Gaussian hypotheses. Besides, the information content of the observations which is used in the reconstruction is computed and studied on the application case. A connection with the degrees of freedom for signal is also established. As a by-product of these methodological developments, conclusions are drawn on the information content of the ETEX dataset as seen from the inverse modelling point of view.
• Probing ETEX-II data set with inverse modelling
  
  • Krysta M.
  • Bocquet Marc
  • Brandt J.
  Atmospheric Chemistry and Physics Discussions, European Geosciences Union, 2008, 8 (1), pp.2795-2819. We give here an account on the results of source inversion of the ETEX-II experiment. Inversion has been performed with the maximum entropy method on the basis of non-zero measurements and in conjunction with a transport model Polair3D. The discrepancy scaling factor between the true and the reconstructed mass has been estimated to be equal to 7. The results contrast with the method's performance on the ETEX-I source. In the latter case its mass has been reconstructed with an accuracy exceeding 80%. The large value of the discrepancy factor for ETEX-II could be ascribed to modelling difficulties, possibly linked not to the transport model itself but rather to the quality of the measurements. (10.5194/acp-8-3963-2008)
  DOI : 10.5194/acp-8-3963-2008
• Calcul du flot optique par assimilation variationnelle de données
  
  • Béréziat Dominique
  • Herlin Isabelle
  , 2008, pp.341-350. Nous proposons de résoudre le problème classique de l'estimation du mouvement dans une séquence d'images en calculant le flot optique. Pour cela, nous utilisons une approche basée sur l'assimilation variationnelle de données qui permet de réaliser une intégration temporelle du calcul du flot optique : les gradients spatiotemporels constituent les observations et sont assimilés dans un modèle de transport du flot optique. Cette approche a deux avantages principaux. D'une part elle permet de définir des modèles d'erreurs qui, in fine, peuvent gérer de façon naturelle les données manquantes. D'autre part, le schéma numérique incrémental sur lequel repose l'assimilation variationnelle de données permet de résoudre efficacement les systèmes non-linéaires. Or, la contrainte du flot optique n'est pas linéaire dans sa forme non différentiée. Notre méthode prend donc en charge l'estimation de grands déplacements.
• Paris-Fog : des chercheurs dans le brouillard
  
  • Bergot Thierry
  • Haeffelin Martial
  • Musson-Genon L.
  • Tardiff R.
  • Colomb M.
  • Boitel Christophe
  • Bouhours G.
  • Bourrianne Thierry
  • Carrer Dominique
  • Challet J.
  • Chazette Patrick
  • Drobinski Philippe
  • Dupont E.
  • Dupont Jean-Charles
  • Elias T.
  • Fesquet C.
  • Garrouste Olivier
  • Gomes Laurent
  • Guerin Alain
  • Lapouge Florian
  • Lefranc Y.
  • Legain Dominique
  • Morange P.
  • Pietras Christophe
  • Plana-Fattori Artemio
  • Protat Alain
  • Rangognio Jerome
  • Raut Jean-Christophe
  • Remy S.
  • Richard D.
  • Romand B.
  • Zhang X.
  La Météorologie, Société météorologique de France (Météo France), 2008, 8 (62), pp.48-58. Une campagne de mesures dédiée au brouillard, appelée Paris-Fog, s'est déroulée en région parisienne au cours de l'hiver 2006-2007. Cette campagne est ambitieuse de par les moyens qui ont été mis en oeuvre et la longueur de la période documentée. On décrit ici les instruments utilisés ainsi que le mode de fonctionnement de la campagne de mesures regroupant des laboratoires de recherche d'horizons différents. Puis on présente un premier bilan ainsi qu'un zoom sur une période d'observations intensives. (10.4267/2042/19175)
  DOI : 10.4267/2042/19175
• Simulation of aerosol optical properties over Europe with a 3-D size-resolved aerosol model: comparisons with AERONET data
  
  • Tombette M.
  • Chazette P.
  • Sportisse B.
  • Roustan Y.
  Atmospheric Chemistry and Physics, European Geosciences Union, 2008, 8 (23), pp.7115-7132. This paper aims at presenting a model-to-data comparison of the Aerosol Optical Thickness (AOT) and of a few sparse data for Single Scattering Albedo (SSA) over Europe for one year. The main contribution of this paper is the sensitivity study to a large number of parameters, including physical and numerical parameters of the aerosol model itself. The optical parameters are computed from a size-resolved aerosol model embedded in the POLYPHEMUS system. The methodology is first described, showing that several hypothesis can be made for micro-physical aerosol properties. The simulation is made over one year (2001); statistics and monthly time series for the simulation and AERONET data are used to evaluate the ability of the model to reproduce AOT and vertically averaged SSA fields and their variability. The relation with the uncertainties of measurements is discussed. Then a sensitivity study with respect to the mixing state of the particle, the way to take into account water uptake, numerical parameters and physical parameteriza-tions of the model is carried out. The results indicate that the mixing state of particles has an influence on optical parameters , as well as the computation of the wet diameter. But some physical and numerical parameters associated with the aerosol model itself have even more influence under certain conditions, through the uncertainties on the aerosol chemical composition, and their size distribution. (10.5194/acp-8-7115-2008)
  DOI : 10.5194/acp-8-7115-2008
• CURIE: a new clear air doppler radar dedicated to the lower part of the atmospheric boundary layer (20 m- 750m)
  
  • Al-Sakka Hassan
  • Weill Alain
  • Le Gac Christophe
  • Ney Richard
  • Dupont E.
  IOP Conference Series: Earth and Environmental Science, IOP Publishing, 2008, 1, pp.012015 (7pp). A new X-band miniradar, the CURIE radar (Canopy Urban Research on Interactions and Exchanges), mainly adapted to low Atmospheric Boundary Layer sounding has been developed at CETP. After a brief description of the opportunity and working conditions in a turbulent atmosphere, main characteristics are presented. Though this radar works in presence of precipitation as all X-band radar can do, this paper is more dedicated to clear air used in the turbulent atmospheric boundary layer. We are presented comparisons with UHF observations and boundary layer information which can be inferred from CURIE as entrainment across the inversion layer. (10.1088/1755-1315/1/1/012015)
  DOI : 10.1088/1755-1315/1/1/012015
• MICS Asia Phase II - Sensitivity to the aerosol module
  
  • Sartelet Karine
  • Hayami Hiroshi
  • Sportisse Bruno
  Atmospheric Environment, Elsevier, 2008, 42 (15), pp.3562-3570. In the framework of the model inter-comparison study - Asia Phase II (MICS2), where eight models are compared over East Asia, this paper studies the influence of different parameterizations used in the aerosol module on the aerosol concentrations of sulfate and nitrate in PM10. An intracomparison of aerosol concentrations is done for March 2001 using different configurations of the aerosol module of one of the model used for the intercomparison. Single modifications of a reference setup for model configurations are performed and compared to a reference case. These modifications concern the size distribution, i.e. the number of sections, and physical processes, i.e. coagulation, condensation/evaporation, cloud chemistry, heterogeneous reactions and sea-salt emissions. Comparing monthly averaged concentrations at different stations, the importance of each parameterization is first assessed. It is found that sulfate concentrations are little sensitive to sea-salt emissions and to whether condensation is computed dynamically or by assuming thermodynamic equilibrium. Nitrate concentrations are little sensitive to cloud chemistry. However, a very high sensitivity to heterogeneous reactions is observed. Thereafter, the variability of the aerosol concentrations to the use of different chemistry transport models (CTMs) and the variability to the use of different parameterizations in the aerosol module are compared. For sulfate, the variability to the use of different parameterizations in the aerosol module is lower than the variability to the use of different CTMs. However, for nitrate, for monthly averaged concentrations averaged over four stations, these two variabilities have the same order of magnitude. (10.1016/j.atmosenv.2007.03.005)
  DOI : 10.1016/j.atmosenv.2007.03.005
• Pollution atmosphérique. Des processus à la modélisation
  
  • Sportisse Bruno
  , 2008, pp.350.