Publications

2017

• Calibrated mitotic oscillator drives motile ciliogenesis
  
  • Al Jord Adel
  • Shihavuddin Asm
  • Servignat D’aout Raphaël
  • Faucourt Marion
  • Genovesio Auguste
  • Karaiskou Anthi
  • Sobczak-Thépot Joëlle
  • Spassky Nathalie
  • Meunier Alice
  Science, American Association for the Advancement of Science (AAAS), 2017, 358 (6364), pp.803-806. Cell division and differentiation depend on massive and rapid organelle remodeling. The mitotic oscillator, centered on the cyclin-dependent kinase 1-anaphase-promoting complex/cyclosome (CDK1-APC/C) axis, spatiotemporally coordinates this reorganization in dividing cells. Here we discovered that nondividing cells could also implement this mitotic clocklike regulatory circuit to orchestrate subcellular reorganization associated with differentiation. We probed centriole amplification in differentiating mouse-brain multiciliated cells. These postmitotic progenitors fine-tuned mitotic oscillator activity to drive the orderly progression of centriole production, maturation, and motile ciliation while avoiding the mitosis commitment threshold. Insufficient CDK1 activity hindered differentiation, whereas excessive activity accelerated differentiation yet drove postmitotic progenitors into mitosis. Thus, postmitotic cells can redeploy and calibrate the mitotic oscillator to uncouple cytoplasmic from nuclear dynamics for organelle remodeling associated with differentiation. (10.1126/science.aan8311)
  DOI : 10.1126/science.aan8311
• Multi-model assessment of PM trends in europe during two decades (1990-2010)
  
  • Tsyro Svetlana
  • Andersson Camilla
  • Bessagnet Bertrand
  • Colette Augustin
  • Couvidat Florian
  • Cuvelier Kees
  • Manders Astrid
  • Mar Kathleen
  • Mircea Mihaela
  • Otero Noelia
  • Aas Wenche
  • Pay Maria-Teresa
  • Raffort Valentin
  • Roustan Yelva
  • Theobald Mark
  • Vivanco Marta G.
  • Briganti Gino
  • Cappelletti Andrea
  • d'Isidoro Massimo
  • Fagerli Hilde
  • Wind Peter
  , 2017, pp.61-64. The model trend analysis for PM10 and PM2.5, performed within the Eurodelta-Trends experiment, covers 21 year, from 1990 through 2010, with particular focus on the period 2001-2010 for which appropriate amount of PM observations is available. Eight chemical transport models (CTM) participated in the multi-modal trend analysis: EMEP/MSC-W, CHIMERE, LOTOS-EUROS, MINNI, MATCH, WRF-Chem, CMAQ and Polyphemus (out of which six models performed trend runs for the 21-year period). The average modelled trends are somewhat smaller than the observed, though the models identify significant PM trends at more sites in the period 2001-2010. There are considerable difference in the PM trends between the regions/countries and in different seasons. Investigation of the changes in PM chemical composition during the investigated period shows that the models differ in terms of relative contribution of the individual PM components to the PM trends. For the 2001-2010 period, the effcct of inter-annual meteorological variability appears more important relative to emission changes. Finally, we look at PM trends/changes during the 1990-2010 period.
• Implementation of a new in-cloud wet deposition scheme into the ldX operational transport modelling
  
  • Quérel Arnaud
  • Quélo Denis
  • Roustan Yelva
  • Mathieu Anne
  , 2017, 2017, pp.858-862. Wet deposition is a key element of the atmospheric transport and deposition modelling. Following the emission and the transport, it is the final process to obtain a map of deposit consecutive to an accidental release. The operational wet deposition schemes of the atmospheric transport modelling are currently rough because a greater accuracy is not required considering the uncertainties on the source term and the meteorological data. However, meteorological data are improving in term of resolution and quality. As a result of this improvement, it may become relevant to use a finer in-cloud wet deposition model, dealing explicitly with the vertical composition of the cloud and the precipitation. In this study, the impact of the integration of the vertical profile of cloud water content and precipitating water is examined on Cs-137 deposition of the Fukushima case. Results show an impact on the final deposit by using vertically resolved deposition schemes. However, these wet deposition schemes will require significant future improvements.
• Uncertainty quantification of pollutant source retrieval: comparison of Bayesian methods with application to the Chernobyl and Fukushima-Daiichi accidental releases of radionuclides
  
  • Liu Y.
  • Haussaire M.
  • Bocquet Marc
  • Roustan Y.
  • Saunier O.
  • Mathieu A.
  Quarterly Journal of the Royal Meteorological Society, Wiley, 2017, 143 (708), pp.2886 - 2901. Inverse modelling of the emissions of atmospheric species and pollutants has significantly progressed over the past 15 years. However, in spite of seemingly reliable estimates, the retrievals are rarely accompanied by an objective estimate of their uncertainty, except when Gaussian statistics are assumed for the errors, which is often an unrealistic assumption. Here, we assess rigorous techniques meant to compute this uncertainty in the context of the inverse modelling of the time emission rates – the so-called source term – of a point-wise atmospheric tracer. Log-normal statistics are used for the positive source term prior and possibly the observation errors; this precludes simple Gaussian statistics-based solutions. Firstly, through the so-called empirical Bayesian approach, parameters of the error statistics – the hyperparameters – are first estimated by maximizing their likelihood via an expectation–maximization algorithm. This enables a robust estimation of a source term. Then, the uncertainties attached to the retrieved source rates and total emission are estimated using four Monte Carlo techniques: (i) an importance sampling based on a Laplace proposal, (ii) a naive randomize-then-optimize (RTO) sampling approach, (iii) an unbiased RTO sampling approach, and (iv) a basic Markov chain Monte Carlo (MCMC) simulation. Secondly, these methods are compared to a more thorough hierarchical Bayesian approach, using an MCMC based on a transdimensional representation of the source term to reduce the computational cost. Those methods, and improvements thereof, are applied to the estimation of the atmospheric caesium-137 source terms from the Chernobyl nuclear power plant accident in April and May 1986 and Fukushima Daiichi nuclear power plant accident in March 2011. This study provides the first consistent and rigorous quantification of the uncertainty of these best estimates. (10.1002/qj.3138)
  DOI : 10.1002/qj.3138
• Simulation of trace metals and PAH atmospheric pollution over Greater Paris: Concentrations and deposition on urban surfaces
  
  • Thouron Laëtitia
  • Seigneur Christian
  • Kim Youngseob
  • Legorgeu Carole
  • Roustan Y.
  • Bruge B.
  Atmospheric Environment, Elsevier, 2017, 167, pp.360 - 376. Urban areas can be subject not only to poor air quality, but also to contamination of other environmental media by air pollutants. Here, we address the potential transfer of selected air pollutants (two metals and three PAH) to urban surfaces. To that end, we simulate meteorology and air pollution from Europe to a Paris suburban neighborhood, using a four-level one-way nesting approach. The meteorological and air quality simulations use urban canopy sub-models in order to better represent the effect of the urban morphology on the air flow, atmospheric dispersion, and deposition of air pollutants to urban surfaces. This modeling approach allows us to distinguish air pollutant deposition among various urban surfaces (roofs, roads, and walls). Meteorological model performance is satisfactory, showing improved results compared to earlier simulations, although precipitation amounts are underestimated. Concentration simulation results are also satisfactory for both metals, with a fractional bias <0.5. Concentrations of benzo[a]pyrene are overestimated, probably because continental emissions may be overestimated. Concentrations of benzo[b]fluoranthene and indeno[1,2,3,cd]pyrene are underestimated, in part because of null boundary conditions. PAH deposition fluxes are consistent with earlier measurements obtained in the Greater Paris region. The model simulation results suggest that both wet and dry deposition processes need to be considered when estimating the transfer of air pollutants to other environmental media. Dry deposition fluxes to various urban surfaces are mostly uniform for PAH, which are entirely present in fine particles. However, there is significantly less wall deposition compared to deposition to roofs and roads for trace metals, due to their coarse fraction. Meteorology, particle size distribution, and urban morphology are all important factors affecting air pollutant deposition. Future work should focus on the collection of data suitable to evaluate the performance of atmospheric models for both wet and dry deposition with fine spatial resolution. (10.1016/j.atmosenv.2017.08.027)
  DOI : 10.1016/j.atmosenv.2017.08.027
• Ensemble forecasting using sequential aggregation for photovoltaic power applications
  
  • Thorey Jean
  , 2017. Our main objective is to improve the quality of photovoltaic power forecasts deriving from weather forecasts. Such forecasts are imperfect due to meteorological uncertainties and statistical modeling inaccuracies in the conversion of weather forecasts to power forecasts. First we gather several weather forecasts, secondly we generate multiple photovoltaic power forecasts, and finally we build linear combinations of the power forecasts. The minimization of the Continuous Ranked Probability Score (CRPS) allows to statistically calibrate the combination of these forecasts, and provides probabilistic forecasts under the form of a weighted empirical distribution function. We investigate the CRPS bias in this context and several properties of scoring rules which can be seen as a sum of quantile-weighted losses or a sum of threshold-weighted losses. The minimization procedure is achieved with online learning techniques. Such techniques come with theoretical guarantees of robustness on the predictive power of the combination of the forecasts. Essentially no assumptions are needed for the theoretical guarantees to hold. The proposed methods are applied to the forecast of solar radiation using satellite data, and the forecast of photovoltaic power based on high-resolution weather forecasts and standard ensembles of forecasts.
• Modelling the impact of viscosity on Secondary Organic Aerosols formation with the SOAP thermodynamic model inside a 3D air quality model
  
  • Couvidat Florian
  • Kim Y.
  • Sartelet Karine
  , 2017. Numerous studies (e.g. Virtanen et al., 2010) show that the partitioning between the gas and particle phases of Semi-Volatile Organic Compounds (SVOC) can differ significantly from thermodynamic equilibrium due to the high viscosity of the organicphase. However, to our knowledge the impact of organic-phase viscosity on Secondary Organic Aerosol formation has never been investigated in 3D air quality models, which usually assume that organic aerosols are not viscous. The impact of the particle viscosity on secondary organic aerosols (SOA) is studied here by coupling an air quality model to the Secondary Organic Aerosol Processor (SOAP Couvidat and Sartelet, 2015) thermodynamic model. SOAP can compute the partitioning of SVOC concentrations either by assuming thermodynamic equilibrium or by computing the dynamic evolution of concentrations according to the kinetics of condensation/evaporation and particle-phase diffusion (as a function of the organic-phase coefficient diffusion). To compute the evolution of the SVOC partitioning, organic particles are separated into several layers with the external layer at the gas/particle interface and the internal layer at the center of the particle. To accurately solve the equations of diffusion of SVOCs inside particles, a high number of layers would be needed (around 100). However, this discretization would lead to a system that is too complex to be implemented in an air quality model. In SOAP, a simplified representation was designed to represent implicitly the diffusion of SVOC inside the particle with a low number of layers (between 2 and 5). A comparison between the explicit representation and the implicit representation of diffusion is shown in Figure 1. SOAP was implemented in the 3D air quality model Polyphemus and SOA concentrations were simulated over Europe during July 2012. Concentrations were simulated assuming either that particles are not viscous (the condensation/evaporation is not limited by the diffusion inside the particle) or that particles are infinitely viscous (the diffusion inside the particle is very slow and compounds do not diffuse inside the particle). Assuming infinitely viscous particles leads to a slight increase of SOA concentrations (SVOC concentrations in the particle phase). Less volatile compounds appear to not be affected by the viscosity of particles, but the concentrations of more volatile compounds increased for viscous particles and could therefore exceed concentrations at equilibrium. Indeed, for volatile organic compounds, in the infinitely viscous simulation the compounds could condense even if the compounds would evaporate for a non-viscous aerosol.
• Modélisation des particules : Participation à Eurodelta et étude au voisinage d'une raffinerie
  
  • Raffort Valentin
  , 2017. Les modèles Eulériens de chimie-transport simulent les phénomènes de formation des polluants atmosphériques dans des mailles de résolution horizontale qui sont généralement de l’ordre de plusieurs kilomètres. Les panaches issus des sources industrielles, de dimensions initiales de l’ordre du mètre, sont donc artificiellement dilués, détériorant alors la représentation de leur impact potentiel sur la qualité de l'air ambiant. Une approche de modèle de panache sous-maille peut-être mise en œuvre pour traiter ce problème. Le modèle de panache sous-maille de Polyphemus traite les émissions des sources ponctuelles industrielles par l'intermédiaire d'un modèle à bouffées gaussiennes qui interagit dynamiquement avec un modèle eulérien. Ceci permet de modéliser la qualité de l’air à grande échelle (régionale à continentale), tout en gardant une bonne représentation des panaches, y compris à l’échelle locale.Les travaux menés dans le cadre de cette thèse ont permis d’améliorer le modèle de panache sous-maille de Polyphemus en intégrant une représentation plus fine de la granulométrie des particules, et d’approfondir les évaluations du modèle à différentes échelles. Ils ont été réalisés selon deux phases principales.La première consiste en l’évaluation à l'échelle continentale du modèle eulérien de Polyphemus dans le cadre de l'exercice d'intercomparaison Eurodelta. La phase actuelle du programme vise à étudier les tendances de pollution à l’échelle de l’Europe sur les vingt dernières années, ainsi que la sensibilité de ces tendances modélisées aux données météorologiques, aux émissions européennes et aux émissions extra-européennes (implicitement représentées par les conditions aux limites). Dans ce contexte, les performances du modèle eulérien de Polyphemus sont évaluées en comparaison à sept autres modèles. Pour cette thèse, l'étude se concentre plus spécifiquement sur l’évaluation de la modélisation des concentrations en aérosols organiques secondaires (AOS), et leurs sensibilités aux différentes paramétrisations utilisées par les modèles participants.La seconde phase présente l’utilisation du modèle de panache sous maille de Polyphemus dans le contexte de différentes campagnes de mesures. En premier lieu, le modèle est appliqué dans le contexte d’une campagne de mesures réalisée en avril 2013 au voisinage de la raffinerie Total de Grandpuits en Seine-et-Marne. Cette étude a permis d'évaluer les performances du modèle à l’échelle de la région Île-de-France et à l'échelle locale. La contribution de la raffinerie aux concentrations en particules inhalables, en interaction avec les autres sources locales, a été analysée. En second lieu, le modèle est appliqué dans le contexte des deux campagnes d'observation du projet TEMMAS (« TEledetection, Measure, Modeling of Atmospherics pollutants on industrial Site »), réalisées au voisinage de la raffinerie Total de La Mède dans les Bouches-du-Rhône en septembre 2015 et février 2016. Les performances du modèle sont évaluées en comparaison à des mesures intensives de concentrations en masse et en nombre et de composition des particules au voisinage de la raffinerie de la Mède (10.70675/26d95be3ze8e9z4c14z987ez56039be1dc04)
  DOI : 10.70675/26d95be3ze8e9z4c14z987ez56039be1dc04
• Méthodes variationnelles d'ensemble itératives pour l'assimilation de données non-linéaire : Application au transport et la chimie atmosphérique
  
  • Haussaire Jean-Matthieu
  , 2017. Les méthodes d'assimilation de données sont en constante évolution pour s'adapter aux problèmes à résoudre dans les multiples domaines d’application. En sciences de l'atmosphère, chaque nouvel algorithme a d'abord été implémenté sur des modèles de prévision numérique du temps avant d'être porté sur des modèles de chimie atmosphérique. Ce fut le cas des méthodes variationnelles 4D et des filtres de Kalman d'ensemble par exemple. La nouvelle génération d'algorithmes variationnels d'ensemble quadridimensionnels (EnVar 4D) ne fait pas exception. Elle a été développée pour tirer partie des deux approches variationnelle et ensembliste et commence à être appliquée au sein des centres opérationnels de prévision numérique du temps, mais n'a à ce jour pas été testée sur des modèles opérationnels de chimie atmosphérique.En effet, la complexité de ces modèles rend difficile la validation de nouvelles méthodes d’assimilation. Il est ainsi nécessaire d'avoir à disposition des modèles d’ordre réduit, qui doivent être en mesure de synthétiser les phénomènes physiques à l'{oe}uvre dans les modèles opérationnels tout en limitant certaines des difficultés liées à ces derniers. Un tel modèle, nommé L95-GRS, a donc été développé. Il associe la météorologie simpliste du modèle de Lorenz-95 à un module de chimie de l'ozone troposphérique avec 7 espèces chimiques. Bien que de faible dimension, il reproduit des phénomènes physiques et chimiques observables en situation réelle. Une méthode d'assimilation de donnée, le lisseur de Kalman d'ensemble itératif (IEnKS), a été appliquée sur ce modèle. Il s'agit d'une méthode EnVar 4D itérative qui résout le problème non-linéaire variationnel complet. Cette application a permis de valider les méthodes EnVar 4D dans un contexte de chimie atmosphérique non-linéaire, mais aussi de soulever les premières limites de telles méthodes.Fort de cette expérience, les résultats ont été étendus au cas d’un modèle réaliste de prévision de pollution atmosphérique. Les méthodes EnVar 4D, via l'IEnKS, ont montré leur potentiel pour tenir compte de la non-linéarité du modèle de chimie dans un contexte maîtrisé, avec des observations synthétiques. Cependant, le passage à des observations réelles d'ozone troposphérique mitige ces résultats et montre la difficulté que représente l'assimilation de données en chimie atmosphérique. En effet, une très forte erreur est associée à ces modèles, provenant de sources d'incertitudes variées. Deux démarches doivent alors être entreprises pour pallier ce problème.Tout d’abord, la méthode d’assimilation doit être en mesure de tenir compte efficacement de l’erreur modèle. Cependant, la majorité des méthodes sont développées en supposant au contraire un modèle parfait. Pour se passer de cette hypothèse, une nouvelle méthode a donc été développée. Nommée IEnKF-Q, elle étend l'IEnKS au cas avec erreur modèle. Elle a été validée sur un modèle jouet, démontrant sa supériorité par rapport à des méthodes d'assimilation adaptées naïvement pour tenir compte de l’erreur modèle.Toutefois, une telle méthode nécessite de connaître la nature et l'amplitude exacte de l'erreur modèle qu'elle doit prendre en compte. Aussi, la deuxième démarche consiste à recourir à des outils statistiques pour quantifier cette erreur modèle. Les algorithmes d'espérance-maximisation, de emph{randomize-then-optimize} naïf et sans biais, un échantillonnage préférentiel fondé sur l'approximation de Laplace, ainsi qu'un échantillonnage avec une méthode de Monte-Carlo par chaînes de Markov, y compris transdimensionnelle, ont ainsi été évalués, étendus et comparés pour estimer l'incertitude liée à la reconstruction du terme source des accidents des centrales nucléaires de Tchernobyl et Fukushima-Daiichi.Cette thèse a donc enrichi le domaine de l'assimilation de données EnVar 4D par ses apports méthodologiques et en ouvrant la voie à l’application de ces méthodes sur les modèles de chimie atmosphérique (10.70675/7fdacc39z3f60z4923z8edfz693835d9c272)
  DOI : 10.70675/7fdacc39z3f60z4923z8edfz693835d9c272
• Modélisation dynamique multi-échelle de la pollution atmosphérique en milieu urbain
  
  • Thouron Laëtitia
  , 2017. La pollution atmosphérique en milieu urbain a été identifiée comme une cause importante d’impacts sanitaires, y compris de décès prématurés. En particulier, les concentrations ambiantes de polluants gazeux tels que le dioxyde d’azote (NO2) et de particules (PM10 et PM2,5) sont réglementées, ce qui implique que des stratégies de réductions d’émissions doivent être mises en place pour diminuer ces concentrations dans les lieux où la réglementation correspondante n’est pas respectée. Par ailleurs, la pollution atmosphérique peut contribuer à la contamination d’autres milieux, par exemple à travers la contribution des dépôts atmosphériques à la contamination des eaux de ruissellement.Les aspects multifactoriels et multiéchelle de la pollution en ville rendent l’identification des sources difficile. En effet, le milieu urbain est un espace hétérogène caractérisé par des structures architecturales complexes (bâti ancien côtoyant un bâti plus moderne, zones résidentielles, commerciales, industrielles, axes routiers…), des émissions de polluants atmosphériques non uniformes et par conséquent une exposition de la population à la pollution qui est variable dans l’espace et le temps.La modélisation de la pollution atmosphérique urbaine a pour vocation de comprendre l’origine des polluants, leur étendue spatiale et leur niveau de concentrations/dépôt. Certains polluants ont des temps de résidence long et peuvent séjourner plusieurs semaines dans l’atmosphère (PM2,5) et donc être transportés sur de longues distances, d’autres au contraire, sont plus locaux (NOx en proximité du trafic). La répartition spatiale d’un polluant dépendra alors de plusieurs facteurs et notamment des surfaces rencontrées. La qualité de l’air, elle, dépend fortement des conditions météorologiques, du bâti (rue-canyon) et des émissions.L’objectif de cette thèse est de traiter certains de ces aspects en modélisant : (1) la pollution urbaine de fond avec un modèle de chimie-transport (Polyphemus/POLAIR3D), qui permet d’estimer les dépôts de polluants atmosphériques par type de surfaces urbaines (toits, murs et chaussées), (2) la pollution à l’échelle de la rue en intégrant explicitement les effets du bâti de manière tridimensionnelle avec d’une part un modèle multiéchelle de chimie-transport (SinG) et d’autre part un modèle de mécanique des fluides (Code_Saturne) et (3) un processus de micro-échelle qui est la réémission des particules présentes sur la chaussée par le trafic routier avec trois formulations différentes (déterministe, semi-empirique et empirique). L’intérêt de cette thèse est de pouvoir comparer et évaluer l’opérabilité et la performance de plusieurs modèles de qualité de l’air à plusieurs échelles (région, quartier et rue) afin de mieux appréhender la caractérisation de la qualité de l’air en milieu urbain (10.70675/a49b6f0bzbd03z4dc4z9e95z2e1276530cdb)
  DOI : 10.70675/a49b6f0bzbd03z4dc4z9e95z2e1276530cdb
• Télédétection satellitaire des surfaces enneigées et englacées
  
  • Rabatel Antoine
  • Berthier Etienne
  • Arnaud Yves
  • Dedieu Jean-Pierre
  • Dumont Marie
  • Gascoin Simon
  • Gay Michel
  • Guerreiro Kévin
  • Karbou Fatima
  • Kouraev Alexei
  • Picard Ghislain
  • Rémy Frédérique
  • Sirguey Pascal
  • Trouvé Emmanuel
  • Zakharova Elena
  La Météorologie, Société météorologique de France (Météo France), 2017 (97), pp.78-85. Cet article présente une vue d'ensemble des avancées récentes en télédétection spatiale appliquée à l'étude des surfaces enneigées et englacées auxquelles la communauté scientifique française a participé. Qu'ils s'agissent de données satellitaires optique, radar, lidar ou gravimétrique, ces travaux sur la couverture nivale saisonnière ou pérenne, les glaciers de montagne, les calottes polaires, la glace de mer ou de lac et de rivière ont pour objectifs de documenter aussi bien les caractéristiques physiques de ces objets que leur variabilité spatio-temporelle aux échelles locale, régionale ou globale. Abstract Satellite remote sensing of snow and ice-covered surfaces (10.4267/2042/62170)
  DOI : 10.4267/2042/62170
• Optimising assimilation of hydrographic profiles into isopycnal ocean models with ensemble data assimilation
  
  • Wang Yiguo
  • Counillon François
  • Bethke Ingo
  • Keenlyside Noel
  • Bocquet Marc
  • Shen Mao-Lin
  Ocean Modelling, Elsevier, 2017, 114, pp.33 - 44. Hydrographic profiles are crucial observational datasets for constraining ocean models and their verti- cal structure. In this study, we investigate a key implementation setup for optimising their assimilation into isopycnal ocean models. For this purpose, we use the Norwegian Climate Prediction Model (Nor- CPM), which is a fully-coupled climate prediction system based on the Norwegian Earth System Model and the ensemble Kalman filter. First, we revisit whether it is more accurate to assimilate observations in their original coordinate (z-level coordinate) or to transform them into isopycnal coordinates prior to assimilation. The analysis is performed with a single assimilation step using synthetic observations that mimic the characteristic properties of hydrographic profiles: varying vertical resolutions, profiles of only temperature and observations only in the top 1000 m. Assimilating profiles in their native coordinate (z- level coordinates) performs best because converting observations into isopycnal coordinates is strongly non-linear which reduces the efficiency of the assimilation. Secondly, we investigate how to set the hori- zontal localisation radius for our system. A radius that varies with latitude following a bimodal Gaussian function fits the system well. Thirdly, we estimate observation error, which consists of both instrumen- tal error and representativeness error. In the proposed formulation only the instrumental error decreases with the number of observations during superobing, because the representativeness error is dominated by model limitation. Finally, we demonstrate the impact of assimilating hydrographic profiles from the observational EN4 dataset into NorCPM. An analysis of 10 years with monthly assimilation is performed with special focus on assessing the accuracy and the reliability of our analysis. The assimilation of hydro- graphic profiles into NorCPM is found to efficiently reduce the model bias and error, and the ensemble spread is found to be a reliable estimator for the forecast error in most regions. (10.1016/j.ocemod.2017.04.007)
  DOI : 10.1016/j.ocemod.2017.04.007
• Cloud diagnosis impact on deposition modelling applied to the Fukushima accident
  
  • Quérel Arnaud
  • Quélo Denis
  • Roustan Yelva
  • Mathieu Anne
  , 2017, 19, pp.EGU2017-8845. In case of a nuclear accident, they are two phases concerning the dispersion of radioactive materials: 1. Forecast: Anticipating the consequences of an atmospheric release of radioactive material. 2. Aftermath: Understand the soil contamination and the possible harm suffered by the populations during the event. Wet deposition modeling is important to achieve these goals. The cloud diagnosis is a key issue for wet deposition modelling since it allows distinguishing between two processes: in-cloud scavenging: the collection of radioactive particles into the cloud below-cloud scavenging: the removal of radioactive material due to the falling drops. Which cloud diagnosis to use for the atmospheric transport models ? Cloud diagnosis choice have a major impact to the volume of the atmosphere considered as-. Then, the repartition between in-cloud and below-cloud may be strongly impacted by the cloud diagnosis. Cloud water mixing ratio (Q C) is the most interesting variable, which describes only the cloud water. Q c provides satisfactory results and is not sensitive to the threshold. We therefore recommend to use Q c to distinguish in-cloud and below-cloud scavenging in the atmospheric transport modelling. Comparison of observed and diagnosed cloud maps, the 16 th March 00:00 EGU 2017 8845 At the Fukushima airport, a deposit as large as 36 kBq.m-2 of Cs-137 was measured. Both dry and wet deposition were probably involved since a raining event occurred on the 15th of March when the plume was passing nearby.
• Degenerate Kalman Filter Error Covariances and Their Convergence onto the Unstable Subspace
  
  • Bocquet Marc
  • Gurumoorthy Karthik S.
  • Apte Amit
  • Carrassi Alberto
  • Grudzien Colin
  • Jones Christopher K. R. T.
  SIAM/ASA Journal on Uncertainty Quantification, ASA, American Statistical Association, 2017, 5 (1), pp.304 - 333. The characteristics of the model dynamics are critical in the performance of (ensemble) Kalman filters. In particular, as emphasized in the seminal work of Anna Trevisan and coauthors, the error covariance matrix is asymptotically supported by the unstable-neutral subspace only, i.e., it is spanned by the backward Lyapunov vectors with nonnegative exponents. This behavior is at the core of algorithms known as assimilation in the unstable subspace, although a formal proof was still missing. This paper provides the analytical proof of the convergence of the Kalman filter covariance matrix onto the unstable-neutral subspace when the dynamics and the observation operator are linear and when the dynamical model is error free, for any, possibly rank-deficient, initial error covariance matrix. The rate of convergence is provided as well. The derivation is based on an expression that explicitly relates the error covariances at an arbitrary time to the initial ones. It is also shown that if the unstable and neutral directions of the model are sufficiently observed and if the column space of the initial covariance matrix has a nonzero projection onto all of the forward Lyapunov vectors associated with the unstable and neutral directions of the dynamics, the covariance matrix of the Kalman filter collapses onto an asymptotic sequence which is independent of the initial covariances. Numerical results are also shown to illustrate and support the theoretical findings. (10.1137/16M1068712)
  DOI : 10.1137/16M1068712
• Four-dimensional ensemble variational data assimilation and the unstable subspace
  
  • Bocquet Marc
  • Carrassi Alberto
  Tellus A: Dynamic meteorology and oceanography, Stockholm University Press, 2017, 69 (1), pp.1304504. The performance of (ensemble) Kalman filters used for data assimilation in the geosciences critically depends on the dynamical properties of the evolution model.Akey aspect is that the error covariance matrix is asymptotically supported by the unstable–neutral subspace only, i.e. it is spanned by the backward Lyapunov vectors with non-negative exponents. The analytic proof of such a property for the Kalman filter error covariance has been recently given, and in particular that of its confinement to the unstable–neutral subspace. In this paper, we first generalize those results to the case of the Kalman smoother in a linear, Gaussian and perfect model scenario. We also provide square-root formulae for the filter and smoother that make the connection with ensemble formulations of the Kalman filter and smoother, where the span of the error covariance is described in terms of the ensemble deviations from the mean. We then discuss how this neat picture is modified when the dynamics are nonlinear and chaotic, and for which analytic results are precluded or difficult to obtain. A numerical investigation is carried out to study the approximate confinement of the anomalies for both a deterministic ensemble Kalman filter (EnKF) and a four-dimensional ensemble variational method, the iterative ensemble Kalman smoother (IEnKS), in a perfect model scenario. The confinement is characterized using geometrical angles that determine the relative position of the anomalies with respect to the unstable–neutral subspace. The alignment of the anomalies and of the unstable–neutral subspace is more pronounced when observation precision or frequency, as well as the data assimilation window length for the IEnKS, are increased. These results also suggest that the IEnKS and the deterministic EnKF realize in practice (albeit implicitly) the paradigm behind the approach of Anna Trevisan and co-authors known as the assimilation in the unstable subspace. (10.1080/16000870.2017.1304504)
  DOI : 10.1080/16000870.2017.1304504
• An iterative ensemble Kalman filter in presence of additive model error
  
  • Sakov Pavel
  • Haussaire Jean-Matthieu
  • Bocquet Marc
  , 2017. The iterative ensemble Kalman filter (IEnKF) in a deterministic framework was introduced in Sakov et al. (2012) to extend the ensemble Kalman filter (EnKF) and improve its performance in mildly up to strongly nonlinear cases. However, the IEnKF assumes that the model is perfect. This assumption simplified the update of the system at a time different from the observation time, which made it natural to apply the IEnKF for smoothing. In this study, we generalise the IEnKF to the case of imperfect model with additive model error. The new method called IEnKF-Q conducts a Gauss-Newton minimisation in ensemble space. It combines the propagated analysed ensemble anomalies from the previous cycle and model noise ensemble anomalies into a single ensemble of anomalies, and by doing so takes an algebraic form similar to that of the IEnKF. The performance of the IEnKF-Q is tested in a number of experiments with the Lorenz-96 model, which show that the method consistently outperforms both the EnKF and the IEnKF naively modified to accommodate additive model noise.
• Caractérisation des sources de polluants atmosphériques et de leurs dépôts sur les bassins versants urbains
  
  • Cherin Nicolas
  , 2017. [L]a pollution de l'air [fait] peser une menace importante sur le plan sanitaire partout dans le monde." L'OMS estime ainsi que, pour l'année 2012 (OMS, 2014), plus de 3,7 millions de décès prématurés dans le monde seraient imputables à la seule pollution de l'air, dont près de 70% surviendraient en ville. Pourtant la connaissance du dépôt sec, particulièrement en milieu urbain, reste très parcellaire. L'object de ce travail de thèse vise à améliorer la compréhension des mécanismes de dépôts atmosphériques en milieu urbain. Historiquement, les dépôts atmosphériques ont été étudiés et modélisés sur des couverts végétaux, plan d'eau ou surface nue, et ce afin d'évaluer, notamment, l'impact sur les écosystèmes des dépôts acides, ou encore de l'eutrophisation. Or, le milieu urbain est caractérisé par une géométrie complexe, et des surfaces variées. Par conséquent, ces modèles de dépôts atmosphériques peuvent ne pas convenir pour simuler les flux de dépôts dans les zones urbaines.Le modèle développé dans cette thèse est un modèle à longueur de mélange. Ces travaux se sont attelés à prendre en compte les principaux processus qui prennent place au sein de la canopée urbaine en modifiant la longueur de mélange et en la rendant dépendante des caractéristiques morphologiques de la ville. Aussi, le profil des vitesses de vent moyen est directement impactée par ce changement de longueur de mélange. Par conséquent, ce nouveau modèle offre la possibilitéde calculer les dépôts secs en milieu urbain en fonction de quelques paramètres représentant les principales caractéristiques de la canopée urbaine (hauteur moyenne des bâtiments, largeur moyenne des rues, densité du bâti) (10.70675/2c3d1ff0za9b4z48cfz9a9azf4c3330eb67b)
  DOI : 10.70675/2c3d1ff0za9b4z48cfz9a9azf4c3330eb67b
• Spatial extent of new particle formation events over the Mediterranean Basin from multiple ground-based and airborne measurements
  
  • Berland Kevin
  • Rose Clémence
  • Pey Jorge
  • Culot Anais
  • Freney Evelyn
  • Kalivitis Nikolaos
  • Kouvarakis Giorgios
  • Cerro José Carlos
  • Mallet Marc
  • Sartelet Karine
  • Beckmann Matthias
  • Bourrianne Thierry
  • Roberts Greg
  • Marchand Nicolas
  • Mihalopoulos Nikolaos
  • Sellegri Karine
  Atmospheric Chemistry and Physics, European Geosciences Union, 2017, 17 (15), pp.9567-9583. Over the last two decades, new particle formation (NPF), i.e., the formation of new particle clusters from gas-phase compounds followed by their growth to the 10–50 nm size range, has been extensively observed in the atmosphere at a given location, but their spatial extent has rarely been assessed. In this work, we use aerosol size distribution measurements performed simultaneously at Ersa (Corsica) and Finokalia (Crete) over a 1-year period to analyze the occurrence of NPF events in the Mediterranean area. The geographical location of these two sites, as well as the extended sampling period, allows us to assess the spatial and temporal variability in atmospheric nucleation at a regional scale. Finokalia and Ersa show similar seasonalities in the monthly average nucleation frequencies, growth rates, and nucleation rates, although the two stations are located more than 1000 km away from each other. Within this extended period, aerosol size distribution measurements were performed during an intensive campaign (3 July to 12 August 2013) from a ground-based station on the island of Mallorca, as well as onboard the ATR-42 research aircraft. This unique combination of stationary and mobile measurements provides us with detailed insights into the horizontal and vertical development of the NPF process on a daily scale. During the intensive campaign, nucleation events occurred simultaneously both at Ersa and Mallorca over delimited time slots of several days, but different features were observed at Finokalia. The results show that the spatial extent of the NPF events over the Mediterranean Sea might be as large as several hundreds of kilometers, mainly determined by synoptic conditions. Airborne measurements gave additional information regarding the origin of the clusters detected above the sea. The selected cases depicted contrasting situations, with clusters formed in the marine boundary layer or initially nucleated above the continent or in the free troposphere (FT) and further transported above the sea. (10.5194/acp-17-9567-2017)
  DOI : 10.5194/acp-17-9567-2017
• Sources and mixing state of summertime background aerosol in the north-western Mediterranean basin
  
  • Arndt Jovanna
  • Sciare Jean
  • Mallet Marc
  • Roberts Greg C.
  • Marchand Nicolas
  • Sartelet Karine
  • Sellegri Karine
  • Dulac François
  • Healy Robert M.
  • Wenger John C.
  Atmospheric Chemistry and Physics, European Geosciences Union, 2017, 17 (11), pp.6975 - 7001. An aerosol time-of-flight mass spectrometer (ATOFMS) was employed to provide real-time single particle mixing state and thereby source information for aerosols impacting the western Mediterranean basin during the ChArMEx-ADRIMED and SAF-MED campaigns in summer 2013. The ATOFMS measurements were made at a ground-based remote site on the northern tip of Corsica. Twenty-seven distinct ATOFMS particle classes were identified and subsequently grouped into eight general categories: EC-rich (elemental carbon), K-rich, Na-rich, amines, OC-rich (organic carbon), V-rich, Fe-rich and Ca-rich particles. Mass concentrations were reconstructed for the ATOFMS particle classes and found to be in good agreement with other co-located quantitative measurements (PM 1 , black carbon (BC), organic carbon, sulfate mass and am-monium mass). Total ATOFMS reconstructed mass (PM 2.5) accounted for 70–90 % of measured PM 10 mass and was comprised of regionally transported fossil fuel (EC-rich) and biomass burning (K-rich) particles. The accumulation of these transported particles was favoured by repeated and extended periods of air mass stagnation over the western Mediterranean during the sampling campaigns. The single particle mass spectra proved to be valuable source markers, allowing the identification of fossil fuel and biomass burning combustion sources, and was therefore highly complementary to quantitative measurements made by Particle into Liquid Sampler ion chromatography (PILS-IC) and an aerosol chemical speciation monitor (ACSM), which have demonstrated that PM 1 and PM 10 were comprised predominantly of sulfate, ammonium and OC. Good temporal agreement was observed between ATOFMS EC-rich and K-rich particle mass concentrations and combined mass concentrations of BC, sulfate, ammonium and low volatility oxygenated organic aerosol (LV-OOA). This combined information suggests that combustion of fossil fuels and biomass produced primary EC-and OC-containing particles, which then accumulated ammonium, sulfate and alkylamines during regional transport. Three other sources were also identified: local biomass burning, marine and shipping. Local combustion particles Published by Copernicus Publications on behalf of the European Geosciences Union. 6976 J. Arndt et al.: Sources and mixing state of summertime background aerosol (emitted in Corsica) contributed little to PM 2.5 particle number and mass concentrations but were easily distinguished from regional combustion particles. Marine emissions comprised fresh and aged sea salt: the former was detected mostly during a 5-day event during which it accounted for 50–80 % of sea salt aerosol mass, while the latter was detected throughout the sampling period. Dust was not efficiently detected by the ATOFMS, and support measurements showed that it was mainly in the PM 2.5–10 fraction. Shipping particles, identified using markers for heavy fuel oil combustion , were associated with regional emissions and represented only a small fraction of PM 2.5 particle number and mass concentration at the site. (10.5194/acp-17-6975-2017)
  DOI : 10.5194/acp-17-6975-2017
• Impact of spaceborne carbon monoxide observations from the S-5P platform on tropospheric composition analyses and forecasts
  
  • Abida Rachid
  • Attié Jean-Luc
  • El Amraoui Laaziz
  • Ricaud Philippe
  • Lahoz William
  • Eskes Henk
  • Segers Arjo
  • Curier Lyana
  • de Haan Johan
  • Kujanpää Jukka
  • Nijhuis Albert Oude
  • Tamminen Johanna
  • Timmermans Renske
  • Veefkind Pepijn
  Atmospheric Chemistry and Physics, European Geosciences Union, 2017, 17 (2), pp.1081-1103. We use the technique of Observing System Simulation Experiments (OSSEs) to quantify the impact of space-borne carbon monoxide (CO) total column observations from the Sentinel-5 Precursor (S-5P) platform on tropospheric analyses and forecasts. We focus on Europe for the period of northern summer 2003, when there was a severe heat wave episode associated with extremely hot and dry weather conditions. We describe different elements of the OSSE: (i) the nature run (NR), i.e., the "truth"; (ii) the CO synthetic observations ; (iii) the assimilation run (AR), where we assimilate the observations of interest; (iv) the control run (CR), in this study a free model run without assimilation; and (v) efforts to establish the fidelity of the OSSE results. Comparison of the results from AR and the CR, against the NR, shows that CO total column observations from S-5P provide a significant benefit (at the 99 % confidence level) at the surface, with the largest benefit occurring over land in regions far away from emission sources. Furthermore, the S-5P CO total column observations are able to capture phenomena such as the forest fires that occurred in Portugal during northern summer 2003. These results provide evidence of the benefit of S-5P observations for monitoring processes contributing to atmospheric pollution. (10.5194/acp-17-1081-2017)
  DOI : 10.5194/acp-17-1081-2017
• EURODELTA-Trends, a multi-model experiment of air quality hindcast in Europe over 1990–2010
  
  • Colette Augustin
  • Andersson Camilla
  • Manders Astrid
  • Mar Kathleen
  • Mircea Mihaela
  • Pay Maria-Teresa
  • Raffort Valentin
  • Tsyro Svetlana
  • Cuvelier Cornelius
  • Adani Mario
  • Bessagnet Bertrand
  • Bergström Robert
  • Briganti Gino
  • Butler Tim
  • Cappelletti Andrea
  • Couvidat Florian
  • d'Isidoro Massimo
  • Doumbia El Hadji Thierno
  • Fagerli Hilde
  • Granier Claire
  • Heyes Chris
  • Klimont Zig
  • Ojha Narendra
  • Otero Noelia
  • Schaap Martijn
  • Sindelarova Katerina
  • Stegehuis Annemiek I.
  • Roustan Yelva
  • Vautard Robert
  • van Meijgaard Erik
  • Vivanco Marta Garcia
  • Wind Peter
  Geoscientific Model Development, European Geosciences Union, 2017, 10 (9), pp.3255 - 3276. The EURODELTA-Trends multi-model chemistry-transport experiment has been designed to facilitate a better understanding of the evolution of air pollution and its drivers for the period 1990–2010 in Europe. The main objective of the experiment is to assess the efficiency of air pollutant emissions mitigation measures in improving regional-scale air quality. The present paper formulates the main scientific questions and policy issues being addressed by the EURODELTA-Trends modelling experiment with an emphasis on how the design and technical features of the modelling experiment answer these questions. The experiment is designed in three tiers, with increasing degrees of computational demand in order to facilitate the participation of as many modelling teams as possible. The basic experiment consists of simulations for the years 1990, 2000, and 2010. Sensitivity analysis for the same three years using various combinations of (i) anthropogenic emissions, (ii) chemical boundary conditions, and (iii) meteorology complements it. The most demanding tier consists of two complete time series from 1990 to 2010, simulated using either time-varying emissions for corresponding years or constant emissions. Eight chemistry-transport models have contributed with calculation results to at least one experiment tier, and five models have – to date – completed the full set of simulations (and 21-year trend calculations have been performed by four models). The modelling results are publicly available for further use by the scientific community. The main expected outcomes are (i) an evaluation of the models' performances for the three reference years, (ii) an evaluation of the skill of the models in capturing observed air pollution trends for the 1990–2010 time period, (iii) attribution analyses of the respective role of driving factors (e.g. emissions, boundary conditions, meteorology), (iv) a dataset based on a multi-model approach, to provide more robust model results for use in impact studies related to human health, ecosystem, and radiative forcing. (10.5194/gmd-10-3255-2017)
  DOI : 10.5194/gmd-10-3255-2017
• An evaluation of the CHIMERE chemistry transport model to simulate dust outbreaks across the Northern hemisphere in march 2014
  
  • Bessagnet Bertrand
  • Menut Laurent
  • Colette Augustin
  • Couvidat Florian
  • Dan Mo
  • Mailler Sylvain
  • Letinois Laurent
  • Pont Véronique
  • Rouil Laurence
  Atmosphere, MDPI, 2017, 8 (12), pp.art. 251. Mineral dust is one of the most important aerosols over the world, affecting health and climate. These mineral particles are mainly emitted over arid areas but may be long-range transported, impacting the local budget of air quality in urban areas. While models were extensively used to study a single specific event, or make a global analysis at coarse resolution, the goal of our study is to simultaneously focus on several affected areas—Europe, North America, Central Asia, east China and the Caribbean area—for a one-month period, March 2014, avoiding any parameter fitting to better simulate a single dust outbreak. The simulation is performed for the first time with the hemispheric version of the CHIMERE model, with a high horizontal resolution (about 10 km). In this study, an overview of several simultaneous dust outbreaks over the Northern Hemisphere is proposed to assess the capability of such modeling tools to predict dust pollution events. A quantitative and qualitative evaluation of the most striking episodes is presented with comparisons to satellite data, ground based particulate matter and calcium measurements. Despite some overestimation of dust concentrations far from emission source areas, the model can simulate the timing of the arrival of dust outbreaks on observational sites. For instance, several spectacular dust storms in the US and China are rather well captured by the models. The high resolution provides a better description and understanding of the orographic effects and the long-range transport of dust plumes. (10.3390/atmos8120251)
  DOI : 10.3390/atmos8120251
• Key Issues for Seamless Integrated Chemistry–Meteorology Modeling
  
  • Baklanov Alexander
  • Brunner Dominik
  • Carmichael Gregory
  • Flemming Johannes
  • Freitas Saulo
  • Gauss Michael
  • Hov Øystein
  • Mathur Rohit
  • Schlünzen K. Heinke
  • Seigneur Christian
  • Vogel Bernhard
  Bulletin of the American Meteorological Society, American Meteorological Society, 2017, 98 (11), pp.2285-2292. (10.1175/bams-d-15-00166.1)
  DOI : 10.1175/bams-d-15-00166.1
• Large eddy simulation of radiation fog: impact of dynamics on the fog life cycle
  
  • Mazoyer Marie
  • Lac Christine
  • Thouron Odile
  • Bergot Thierry
  • Masson Valéry
  • Musson-Genon Luc
  Atmospheric Chemistry and Physics, European Geosciences Union, 2017, 17 (21), pp.13017-13035. Large eddy simulations (LESs) of a radiation fog event occurring during the ParisFog experiment are studied with a view to analyse the impact of the dynamics of the boundary layer on the fog life cycle. The LES, performed with the Meso-NH model at 5m resolution horizontally and 1m vertically, and with a 2-moment microphysical scheme, includes the drag effect of a tree barrier and the deposition of droplets on vegetation. The model shows good agreement with measurements of near-surface dynamic and thermodynamic parameters and liquid water path. The blocking effect of the trees induces elevated fog formation, as actually observed, and horizontal heterogeneities during the formation. It also limits cooling and cloud water production. Deposition is found to exert the most significant impact on fog prediction as it not only erodes the fog near the surface but also modifies the fog life cycle and induces vertical heterogeneities. A comparison with the 2m horizontal resolution simulation reveals small differences, meaning that grid convergence is achieved. Conversely, increasing numerical diffusion through a wind advection operator of lower order leads to an increase in the liquid water path and has a very similar effect to removing the tree barrier. This study allows us to establish the major dynamical ingredients needed to accurately represent the fog life cycle at very high-resolution. (10.5194/acp-17-13017-2017)
  DOI : 10.5194/acp-17-13017-2017
• Who is the Expert? Integrated Urban Modeling and the Reconfiguration of Expertise
  
  • Commenges Hadrien
  • Tomasoni Lorenza
  • Seigneur Christian
  • Bonin Olivier
  • Leurent Fabien
  • Bonhomme Céline
  • Deroubaix José-Frédéric
  Journal of Urban Technology, Taylor & Francis (Routledge): SSH Titles, 2017, 24 (2), pp.89-108. Much has been spoken and written about the rationalization and optimization of services and amenities in urban territories. In this context, there is increasing use of numerical modeling techniques addressing the design, selection and/or calibration of policy instruments. The question of the relations between appraisal tools and policymaking has been widely studied. However, few studies have specifically focused on the role of modeling in policymaking processes. Drawing on two case studies, this paper suggests a change in the nature of multi-expertise: neither conflicting nor cross-sectoral, we observed in both cases an interwoven configuration with a network of experts making use of integrated models. We call this configuration distributed expertise, arguing that it is a novel configuration and that its emergence is closely linked to the development of integrated modeling techniques. Other authors have discussed the idea that the growing need for new appraisal tools is linked with the proliferation of wicked policy problems. From our case studies we would conclude that the emergence of integrated modeling is not a response to complex problems but to complex systems of actors who need to reach a consensus on actions. (10.1080/10630732.2017.1284990)
  DOI : 10.1080/10630732.2017.1284990