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International audience; The international research program “ReNovRisk-CYCLONE” (RNR-CYC, 2017–2021) directly involves 20 partners from 5 countries of the south-west Indian-Ocean. It aims at improving the observation and modelling of tropical cyclones in the south-west Indian Ocean, as well as to foster regional cooperation and improve public policies adapted to present and future tropical cyclones risk in this cyclonic basin. This paper describes the structure and main objectives of this ambitious research project, with emphasis on its observing components, which allowed integrating numbers of innovative atmospheric and oceanic observations (sea-turtle borne and seismic data, unmanned airborne system, ocean gliders), as well as combining standard and original methods (radiosoundings and global navigation satellite system (GNSS) atmospheric soundings, seismic and in-situ swell sampling, drone and satellite imaging) to support research on tropical cyclones from the local to the basin-scale.

This repository contains the data and scripts required to reproduce the results of the paper "Characterizing Convection Schemes Using Their Responses to Imposed Tendency Perturbations" submitted to the Journal of Advances inModeling Earth Systems (JAMES). Brief description of project An SCM intercomparison project based on the Linear Response Function framework of Kuang (2010), where we examine the temperature and moisture responses to small convective tendency perturbations. Participating Single-Column Models (SCMs): WRF, LMDZ, CNRM, UM, SCAM Convection schemes tested: WRF Kain-Fritsch WRF New-Tiedtke WRF New-Simplified-Arakawa-Schubert WRF Betts-Miller-Janjic WRF Zhang-McFarlane CNRM PCMT scheme UM Simplified-Betts-Miller UM Mass-Flux scheme (Gregory & Rowntree) SCAM Zhang-McFarlane LMDZ modified-Emanuel scheme + Cold pool formulation Repository structure /data directory: contains the data from the SCMs, in csv format /data/[model_name]/ directories: contain the data of the individual models. There are four sub-directories (five for WRF) for each model: REF directory: contains data for RCE mean state, including Temperature (T) and Relative Humidity (RH) matrix_X_raw directory: contains raw data for the T and q responses to dT/dt and dq/dt perturbations matrix_M_inv directory: contains the post-processed (normalized and standardized) M-1 matrix data response_profiles directory: contains the post-processed response profiles (vertical column) for perturbation at two levels (850 and 650 hPa) (for WRF only) pbl_mp_sensitivity directory: data for WRF PBL and MP sensitivity tests. There are three sub-directories in this folder: mean_states directory: contains data for the RCE mean state sensitivity to PBL and MP schemes response_profiles directory: contains data for the sensitivity of T and q responses to PBL and MP schemes response_profiles_non_idealized directory: contains data to compare sensitivity of T and q responses to PBL and MP schemes between idealized and non-idealized setups /scripts directory: contains the python scripts to post-process and plot the figures in the paper /scripts/plot_inidividual_matrix/ directory: contains scripts to plot the M-1 matrix and the 2-levels response profiles for individual SCMs plot_matrix.py : script to post-process and plot the matrix and response profiles for selected SCM using the raw data in the matrix_X_raw folders. Option available to save the (post-processed) outputs as csv files in the matrix_M_inv and response_profiles folders of the selected SCM /scripts/plot_figures/ directory: contains scripts to plot the Figures in the paper plot_rce_mean_states_all_models.py : script to plot Figure 1 (RCE mean state T and RH of all SCMs) plot_anomaly_profiles.py : script to plot Figure 2 - 3 (vertical profiles of T and q responses for selected SCMs) plot_matrix_all_models.py : script to plot Figures 4 - 7 (M-1 matrices of all SCMs) plot_rh_q_correlation_matrix.py : script to plot Figure 8 (correlation matrix of RH vs. q') plot_pbl_mp_sensitivity_mean_states.py : script to plot Figures 9 - 10 (sensitivity of RCE mean state to PBL and MP schemes) plot_pbl_mp_sensitivity_responses.py : script to plot Figures 11 - 12 (sensitivity of T and q responses to PBL and MP schemes) plot_pbl_mp_sensitivity_responses_non_idealized.py : script to plot Figures A1 - A2 (sensitivity of T and q responses to PBL and MP schemes comparison between idealized and non-idealized setups) &nbsp

Monsoons govern the climate of a large part of Asia from the Indian subcontinent to eastern China today. However, their establishment and evolution remain debated and are regularly re-evaluated thanks to the acquisition of new climate indicators. Recent data suggest that the monsoon regime in Asia was already in place about s 40Ma ago, in the late Eocene, in a globally warmer climate context and in a paleogeographic configuration very different from today. The aim of this thesis is to study the conditions for the development of Asian monsoons during the period 42-33Ma, encompassing the late Eocene and the major climatic transition from Eocene to Oligocene. We investigate the different fields of persistent uncertainties for this period (paleogeography, pCO2, sea level) and the different sources of climatic variability (mainly orbital forcing). We use the earth system model IPSL-CM5A2, recently adapted to the study of paleoclimates. Using a first late Eocene paleogeography and a pCO2 of 1120 ppm, we first show that the model simulates extremely seasonal rainfall in Asia, without presenting the atmospheric circulation characteristic of monsoons. The sensitivity of the late-Eocene climate and vegetation cover to the orbital parameters is then evaluated through various sensitivity tests. We show that orbital variations may have been a major forcing of climate and biological variability in Asia. Configurations favouring strong inter-hemispheric thermal gradients (via strong obliquities and/or precessions inducing warm boreal summers), by causing increased migration of humid equatorial air masses over the continent, generate seasonally very humid climates in summer over Southeast Asia. More generally, the vegetation cover also appears to be very sensitive to orbital variations in the subtropics and high latitudes. These results open new perspectives for reflection on possible relationships between orbital forcing, climate and the opening of dispersal corridors for Asian fauna towards Europe and America (the so-called Grande Coupure phenomenon). Finally, we compare the atmospheric circulations generated by alternative paleogeographic reconstructions of the Asian region. They test, for example, different altitudes of the Tibetan plateau and different morphologies of the initial phase of the collision between India and Asia, both of which are still the subject of much debate. Finally, these results are put into perspective by comparing them with climate simulations at ∼34, ∼20 and ∼10 Ma. The simulated climate in Asia finally appears to be very insensitive to local changes in the Indo-Tibetan paleogeography. Conversely, we note the progressive appearance of the pressure fields and winds characteristic of monsoons as the withdrawal of the Paratethys Sea and the closure of the Neotethys Ocean allows the exposure of the Arabian Peninsula and Central Asia, thus greatly increasing the continentality of the region. We thus suggest that the thermal gradients induced by the Asian continentality on a geological time scale, or by favourable orbital parameters on a time scale of a few thousand years, constitute the dominant forcings of the monsoon regime in Asia., Les moussons régissent le climat d’une large partie de l’Asie depuis le subcontinent indien jusqu’à l’est de la Chine actuellement. Leur mise en place et leur évolution restent cependant débattues et sont régulièrement réévaluées grâce à l’acquisition de nouveaux indicateurs climatiques. Des données récentes suggèrent que le régime de mousson en Asie fonctionnait déjà il y a environ 40 Ma, à l’Éocène supérieur, dans un contexte climatique globalement plus chaud et dans une configuration paléogéographique très différente d’aujourd’hui. Le but de cette thèse est d’étudier les conditions d’une mise en place des moussons asiatiques au cours de la période 42-33 Ma, englobant la fin de l’Éocène et la transition climatique majeure de l’Éocène-Oligocène. Nous balayons les différents champs d’incertitudes persistantes pour cette époque (paléogéographie, pCO2, niveau marin) et les différentes sources de variabilité climatique (le forçage orbital essentiellement). Nous utilisons le modèle de système- Terre IPSL-CM5A2, récemment adapté à l’étude des paléoclimats. En utilisant une première paléogéographie tardi-Éocène et une pCO2 de 1120 ppm, nous montrons dans un premier temps que le modèle simule des précipitations extrêmement saisonnières en Asie, sans pour autant présenter la circulation atmosphérique caractéristique des moussons. La sensibilité du climat et du couvert végétal tardi-Éocène aux paramètres orbitaux est ensuite évaluée à travers différents tests de sensibilité. Nous démontrons que les variations orbitales ont pu être un forçage majeur de variabilité climatique et biologique en Asie. Les configurations favorisant des gradients thermiques inter-hémisphériques importants (via des obliquités fortes et/ou des précessions induisant des étés boréaux chauds), en provoquant une migration accrue des masses d’air équatoriales humides sur le continent, génèrent des climats saisonnièrement très humides en été sur le sud-est asiatique. Plus globalement, le couvert végétal semble également très sensible aux variations orbitales dans les subtropiques et aux hautes latitudes. Ces résultats ouvrent de nouvelles pistes de réflexion sur de possibles relations entre forçage orbital, climat et ouverture de corridors de dispersion des faunes asiatiques vers l’Europe et l’Amérique (phénomènes nommés Grande Coupure). Enfin, nous comparons les circulations atmosphériques générées par des reconstructions paléogéographiques alternatives de la région asiatique. Elles testent par exemple différentes altitudes du plateau tibétain et différentes morphologies de la phase initiale de collision entre l’Inde et l’Asie, ces deux aspects étant encore extrêmement débattus. Pour finir, ces résultats sont mis en perspective en les comparant à des simulations climatiques à ∼34, ∼20 et ∼10 Ma. Le climat simulé en Asie apparaît finalement très peu sensible aux changements locaux de la paléogéographie indo-tibétaine. À l’inverse, nous notons l’apparition progressive des champs de pressions et des vents caractéristiques des moussons à mesure que le retrait de la mer Paratéthys et de la fermeture de l’océan Néotéthys permet l’exondation de la péninsule arabique et de l’Asie centrale, augmentant ainsi fortement la continentalité de la région. Nous suggérons ainsi que les gradients thermiques induits par la continentalité asiatique sur une échelle de temps géologique, ou par des paramètres orbitaux favorables sur une échelle de temps de quelques milliers d’années constituent les forçages dominants du régime des moussons en Asie.

International audience; This work is motivated by the identification of the land-atmosphere interactions as one of the key sources of uncertainty in climate change simulations. It documents new developments in related processes, namely, boundary layer/convection/clouds parameterizations and land surface parameterization in the Earth System Model of the Institut Pierre Simon Laplace (IPSL). Simulations forced by prescribed oceanic conditions are produced with different combinations of atmospheric and land surface parameterizations. They are used to explore the sensitivity to the atmospheric physics and/or soil physics of • major biases in the near surface variables over continents, • the energy and moisture coupling established at the soil/atmosphere interface in not too wet (energy limited) and not too dry (moisture limited) soil moisture regions also known as transition or "hot-spot" regions, • the river runoff at the outlet of major rivers. The package implemented in the IPSL-Climate Model for the Phase 6 of the Coupled Models Intercomparison Project (CMIP6) allows us to reduce several biases in the surface albedo, the snow cover, and the continental surface air temperature in summer as well as in the temperature profile in the surface layer of the polar regions. The interactions between soil moisture and atmosphere in hotspot regions are in better agreement with the observations. Rainfall is also significantly improved in volume and seasonality in several major river basins leading to an overall improvement in river discharge. However, the lack of consideration of floodplains and human influences in the model, for example, dams and irrigation, impacts the realism of simulated discharge. Plain Language Summary Land surface-atmosphere interactions play an essential role in the climate system. They strongly modulate the regional climates and have impacts on the global scale for instance through freshwater release into the oceans. Climate hazards (heat waves, droughts) and their impacts on populations also strongly depend on interactions between land and atmosphere and on their evolution with climate change. Climate models are precious tools to investigate how the Earth climate behaves. The sixth phase of the Climate Model Intercomparison Project (CMIP6) provides important tools to measure the progress and address the remaining open questions regarding the continental climate modeling. The representation of the land-atmosphere coupled system by the IPSL-Climate Model involved in CMIP6 is thoroughly evaluated against observations and compared with simulations using the CMIP5 version. Several biases concerning the temperature over land and over the ice sheets and with the snow cover are significantly reduced. Numerous improvements were made developping advanced parameterizations and tuning of the radiation and of the turbulent mixing in the atmospheric model. The realism of the seasonal

This thesis focuses on the study of Titan's atmosphere ans its seasonal variations, with a Global Climate Model (GCM). The longevity of the Cassini-Huygens mission having made it possible to map the atmosphere for half a Titan-year, many seasonal phenomena have been highlighted, concerning the evolution of temperature in the polar stratospheric regions, the role of trace compounds, or the polar clouds at high altitude. A global understanding of these mechanisms is achieved through tools such as GCMs. As the IPSL Titan GCM preexisting before this thesis did not satisfactorily address these problems, as it suffered from a poor representation of the temperature in the stratosphere, we set up a new radiative transfer scheme. This revision extends to the entire coupling with photochemical and microphysical modules. A method is developed to take into account the opacities variations of trace compounds induced by seasonal changes. Since the preexisting microphysical model has many limitations, a new one is being implemented. Fully coupled dynamic-physical-photochemical-microphysical simulations can thus be performed. They enable the study of the influence of the couplings on the thermal structure and atmospheric dynamics. Sepcial attention is brought to bear on the stratospheric polar regions where the mechanisms at work in the circulation reversal are compared to Cassini data. Finally, the seasonal evolution of the compounds is discussed and the role of couplings is analyzed., Cette thèse porte sur l'étude de l'atmosphère de Titan et ses variations saisonnières, avec un modèle de climat global (GCM). La longévité de la mission Cassini-Huygens ayant permis de cartographier l'atmosphère pendant une demi-année titanienne, de nombreux phénomènes saisonniers ont été mis en évidence, concernant l'évolution de la température dans les régions stratosphériques polaires, le rôle des composés traces, ou les nuages polaires à haute altitude. Une compréhension de ces mécanismes passe par le biais d'outils comme les GCM. Le GCM Titan de l'IPSL existant avant ces travaux ne permettant pas d'aborder correctement ces problèmes, car souffrant d'une mauvaise représentation de la température dans la stratosphère, on met en place un nouveau transfert radiatif. Cette refonte s'étend à l'ensemble des couplages avec les modules photochimiques et microphysiques. On développe notamment une méthode pour prendre en compte les variations d'opacité des composés traces induites par les changements saisonniers - méthode potentiellement applicable à d'autres objets. Le modèle microphysique existant ayant de nombreuses limitations, on en implémente un nouveau. Des simulations entièrement couplées dynamique-physique-photochimie-microphysique peuvent ainsi être réalisées. Avec celles-ci on étudie l'influence des couplages sur la structure thermique et la dynamique atmosphérique. Une attention particulière est portée sur les régions polaires stratosphériques, où les mécanismes œuvrant dans le renversement de la circulation sont comparés aux observations de Cassini. Enfin, l'évolution saisonnière des composés est discutée et le rôle des couplages est analysé.

Aiming to generate realistic synthetic times series of the bivariate process of daily mean temperature and precipitations, we introduce a non-homogeneous hidden Markov model. The non-homogeneity lies in periodic transition probabilities between the hidden states, and time-dependent emission distributions. This enables the model to account for the non-stationary behaviour of weather variables. By carefully choosing the emission distributions, it is also possible to model the dependance structure between the two variables. The model is applied to several weather stations in Europe with various climates, and we show that it is able to simulate realistic bivariate time series.

This thesis deals with the study of the climate of West Africa using the global model developed at the Pierre Simon Laplace Institute and observations mainly acquired during the Multidisciplinary Analysis campaign of the African Monsoon AMMA. The work of the thesis aims more specifically at improving the representation of the West African climate by reducing the biases observed in the intercomparison exercise of coupled models CMIP5, in particular from atmosphere-surface interactions, with the aim of better predict the distribution of rainfall over the region but also extreme events such as heat waves. The results showed that the representation of seasonality of temperatures and rainfall in West Africa was altered by strong biases on the surface energy budget and large-scale circulation (latitudinal positioning of the key elements of the monsoon). The first part of the work consists of implementing an evaluation technique based on two experimental protocols and aimed at: i) distinguishing the biases due to the circulation of those due to the energy budget at the surface, ii) facilitating the exploitation of data on sites, iii) isolating the effect of parameterizations. In this section, the biases on circulation and water budget are illustrated. This study first demonstrates the great interest of the nudging method for the confrontation of a GCM with station data and for analyzing the effect of model parameterizations in West Africa. Then, The in-situ data are used to: 1) identify the biases on the energy budget, 2) link these biases to the defects of the parameterizations used in order to find ways to improve. With this study, a number of problems, such as a poor specification of bare soil albedo and different plant functional type or "bug" in the coupling between thermal inertia and soil moisture have been identified . Some are now corrected in recent versions of the model developed for the CMIP6 exercise. Also in this manuscript, we show the progress achieved through this methodology on the representation of the water and energy budget, as well as the remaining problems. Finally, one of the major aims of this study is the work on the role of aerosols in the representation of the West African climate and in the setting up of heat waves. In this part, we introduced a representation of dust interactive with meteorology and calculated its impact on the representation of the energy budget at the surface. Then, in the framework of the ANR ACASIS, we studied the heat wave of 2010. This work allowed us to highlight the link between aerosols and the increase of precipitable spring water and to demonstrate by this is the importance of aerosols in the representation of heat waves. Finally, we discussed the issue of dynamic-physical coupling using a new experimental protocol and through the analysis of the aerosols impact on monsoon rains.; Cette thèse porte sur l'étude du climat de l'Afrique de l'Ouest à l'aide du modèle global développé à l'Institut Pierre Simon Laplace et des observations principalement acquises pendant la campagne d'Analyse Multidisciplinaire de la Mousson Africaine AMMA. Les travaux de la thèse visent plus spécifiquement à améliorer la représentation du climat ouest africain par la réduction des biais relevés dans l'exercice d'inter-comparaison des modèles couplés CMIP5 provenant en particulier des interactions atmosphère-surface, dans l'objectif de mieux prédire la distribution des pluies sur la région mais également des événements extrêmes tels que les vagues de chaleur. Les résultats ont montré que la représentation de la saisonnalité des températures et des précipitations en Afrique de l'ouest était altérée par de forts biais sur le bilan d'énergie à la surface et la circulation de grande-échelle ( positionnement latitudinale des éléments clés de la mousson). La première partie du travail consiste à mettre en place une technique d'évaluation basée sur deux protocoles expérimentaux et visant à : i) distinguer les biais dus à la circulation de ceux dus au bilan d'énergie à la surface , ii) faciliter l'exploitation des données sur sites, iii) isoler l'effet des paramétrisations. Dans cette partie, les biais sur la circulation et le le bilan d'eau sont illustrés. L'importance de l 'utilisation des techniques de guidage des vents horizontaux pour l'exploitation des mesures sur sites et pour l'analyse de l'effet des paramétrisations du modèle en Afrique de l'ouest est mise en lumière. Les données in-situ sont ensuite utilisées afin: 1) d'identifier les biais sur le bilan d'énergie, 2) relier ces biais aux défauts des paramétrisations utilisées dans le but de trouver des pistes d'amélioration. Grâce à cette étude, un certain nombre de problèmes, comme une mauvaise spécification de l'albédo de sol nu et des différents types de plante ou des "bug" sur le fonctionnement dans le couplage entre inertie thermique et humidité des sols, ont été identifiés. Certains sont dorénavant corrigés dans les versions récentes du modèle développées pour l'exercice CMIP6. Aussi dans ce manuscrit, nous montrons les progrès réalisés grâce à cette méthodologie sur la représentation du bilan d'eau et d'énergie, ainsi que les problèmes qui subsistent. Enfin, La dernière étude rassemble les travaux sur le rôle des aérosols dans la représentation du climat ouest africain et dans la mise en place des vagues de chaleur. Dans cette partie, nous avons introduit des poussières interactives avec la météorologie et calculé leur impact sur la représentation du bilan d'énergie à la surface. Puis, dans le cadre de l'ANR ACASIS, nous avons étudié la vague de chaleur de 2010. Ce travail nous a permit de mettre en exergue le lien entre les aérosols et l'augmentation de l'eau précipitable au printemps et de démontrer par ce fait l'importance des aérosols dans la représentation des vagues chaleur. Pour finir, nous avons abordé la question du couplage dynamique-physique à l'aide d'un nouveau protocole expérimental et à travers l'analyse de l'impact des aérosols sur les pluies de mousson.

This thesis deals with the study of the climate of West Africa using the global model developed at the Pierre Simon Laplace Institute and observations mainly acquired during the Multidisciplinary Analysis campaign of the African Monsoon AMMA. The work of the thesis aims more specifically at improving the representation of the West African climate by reducing the biases observed in the intercomparison exercise of coupled models CMIP5, in particular from atmosphere-surface interactions, with the aim of better predict the distribution of rainfall over the region but also extreme events such as heat waves. The results showed that the representation of seasonality of temperatures and rainfall in West Africa was altered by strong biases on the surface energy budget and large-scale circulation (latitudinal positioning of the key elements of the monsoon). The first part of the work consists of implementing an evaluation technique based on two experimental protocols and aimed at: i) distinguishing the biases due to the circulation of those due to the energy budget at the surface, ii) facilitating the exploitation of data on sites, iii) isolating the effect of parameterizations. In this section, the biases on circulation and water budget are illustrated. This study first demonstrates the great interest of the nudging method for the confrontation of a GCM with station data and for analyzing the effect of model parameterizations in West Africa. Then, The in-situ data are used to: 1) identify the biases on the energy budget, 2) link these biases to the defects of the parameterizations used in order to find ways to improve. With this study, a number of problems, such as a poor specification of bare soil albedo and different plant functional type or "bug" in the coupling between thermal inertia and soil moisture have been identified . Some are now corrected in recent versions of the model developed for the CMIP6 exercise. Also in this manuscript, we show the progress achieved through this methodology on the representation of the water and energy budget, as well as the remaining problems. Finally, one of the major aims of this study is the work on the role of aerosols in the representation of the West African climate and in the setting up of heat waves. In this part, we introduced a representation of dust interactive with meteorology and calculated its impact on the representation of the energy budget at the surface. Then, in the framework of the ANR ACASIS, we studied the heat wave of 2010. This work allowed us to highlight the link between aerosols and the increase of precipitable spring water and to demonstrate by this is the importance of aerosols in the representation of heat waves. Finally, we discussed the issue of dynamic-physical coupling using a new experimental protocol and through the analysis of the aerosols impact on monsoon rains.; Cette thèse porte sur l'étude du climat de l'Afrique de l'Ouest à l'aide du modèle global développé à l'Institut Pierre Simon Laplace et des observations principalement acquises pendant la campagne d'Analyse Multidisciplinaire de la Mousson Africaine AMMA. Les travaux de la thèse visent plus spécifiquement à améliorer la représentation du climat ouest africain par la réduction des biais relevés dans l'exercice d'inter-comparaison des modèles couplés CMIP5 provenant en particulier des interactions atmosphère-surface, dans l'objectif de mieux prédire la distribution des pluies sur la région mais également des événements extrêmes tels que les vagues de chaleur. Les résultats ont montré que la représentation de la saisonnalité des températures et des précipitations en Afrique de l'ouest était altérée par de forts biais sur le bilan d'énergie à la surface et la circulation de grande-échelle ( positionnement latitudinale des éléments clés de la mousson). La première partie du travail consiste à mettre en place une technique d'évaluation basée sur deux protocoles expérimentaux et visant à : i) distinguer les biais dus à la circulation de ceux dus au bilan d'énergie à la surface , ii) faciliter l'exploitation des données sur sites, iii) isoler l'effet des paramétrisations. Dans cette partie, les biais sur la circulation et le le bilan d'eau sont illustrés. L'importance de l 'utilisation des techniques de guidage des vents horizontaux pour l'exploitation des mesures sur sites et pour l'analyse de l'effet des paramétrisations du modèle en Afrique de l'ouest est mise en lumière. Les données in-situ sont ensuite utilisées afin: 1) d'identifier les biais sur le bilan d'énergie, 2) relier ces biais aux défauts des paramétrisations utilisées dans le but de trouver des pistes d'amélioration. Grâce à cette étude, un certain nombre de problèmes, comme une mauvaise spécification de l'albédo de sol nu et des différents types de plante ou des "bug" sur le fonctionnement dans le couplage entre inertie thermique et humidité des sols, ont été identifiés. Certains sont dorénavant corrigés dans les versions récentes du modèle développées pour l'exercice CMIP6. Aussi dans ce manuscrit, nous montrons les progrès réalisés grâce à cette méthodologie sur la représentation du bilan d'eau et d'énergie, ainsi que les problèmes qui subsistent. Enfin, La dernière étude rassemble les travaux sur le rôle des aérosols dans la représentation du climat ouest africain et dans la mise en place des vagues de chaleur. Dans cette partie, nous avons introduit des poussières interactives avec la météorologie et calculé leur impact sur la représentation du bilan d'énergie à la surface. Puis, dans le cadre de l'ANR ACASIS, nous avons étudié la vague de chaleur de 2010. Ce travail nous a permit de mettre en exergue le lien entre les aérosols et l'augmentation de l'eau précipitable au printemps et de démontrer par ce fait l'importance des aérosols dans la représentation des vagues chaleur. Pour finir, nous avons abordé la question du couplage dynamique-physique à l'aide d'un nouveau protocole expérimental et à travers l'analyse de l'impact des aérosols sur les pluies de mousson.

Observation of the Atmospheric Boundary Layers (ABL) above the Antarctic Plateau has revealed the strongest near-surface temperature stratifications on the Earth. A correct parametrization of the very stratified Antarctic ABLs in General Circulation Models (GCM) is critical since they exert a strongcontrol on the continental scale temperature inversion, on the coastal katabatic winds and subsequently on the Southern Hemisphere circulation. The previous Gewex Atmospheric Boundary Layer Studies (GABLS) highlighted that the parametrization of the very stratified, or very stable, ABLs isone of the most critical challenge in the atmospheric modelers community. Indeed, the nature of the mixing processes are not completely understood and the commonly used similarity laws, on which the model’s parametrization are usually based, are no longer valid. The aim of this PhD work is to evaluate and improve the modelling of the ABL over the Antarctic Plateau by the Laboratoire de Météorologie Dynamique-Zoom (LMDZ) GCM, the atmospheric component of the IPSL Earth System Model in preparation for the sixth Coupled Models Intercomparison Project. Before the model evaluation itself, an in-depth study of the dynamics of the atmospheric surface layer and of the stable ABL over the Antarctic Plateau was carried out from in situ measurements at Dome C. The analysis enabled the first estimations of the roughness length and of the surface fluxes during the polar night at this location as well as the characterization of very frequent occurences of near-surface moisture supersaturations with respect to ice. Investigation of meteorological measure-ments along a 45 m tower also revealed two distinct dynamical regimes of the stable ABL at this location. In particular, the relation between the near surface inversion amplitude and the wind speed takes a typical ’reversed S-shape’, suggesting a system obeing with an hysteresis. A further analysisshowed that this is a clear illustration of a general and robust feature of the stable ABL systems, corresponding to a ‘critical transition’ between a steady turbulent and a steady ‘radiative’ regime. LMDZ was then run on 1D simulations during a typical clear-sky summertime diurnal cycle in the framework of the fourth GABLS case. Sensitivity tests to surface parameters, vertical grid and turbulent mixing parametrizations were performed leading to significant improvements of the model and to a new configuration better adapted for Antarctic conditions. 3D simulations were then carried outwith the ’zooming capability’ of the horizontal grid and with nudging. These simulations enabled a further evaluation of the model over a full year and extending the analysis beyond Dome C. In particular, this study raised the importance of the radiative scheme and of the surface layer scheme forthe modelling of the ABL during the polar night over the Plateau. Finally, the PhD work extented toward the modelling of the stable ABL over the other continents, assessing how the frequently underestimated subgrid mixing of momentum and heat can be compensated by a transfer of large scalekinetic energy toward turbulent kinetic energy when the flow is slowed down by orographic gravity wave drag., L’observation des couches limites atmosphériques au dessus du plateau antarctique a mis en évidence les plus fortes inversions de température proches de la surface de la planète. Bien paramétriser ces couches limites extrêmes dans un modèle de circulation générale est essentiel pour represéntercorrectement l’inversion climatologique de température au dessus du plateau, mais également pour reproduire des vents catabatiques réalistes en aval du plateau et de surcroit, une circulation atmosphérique correcte dans l’hémisphère sud. Les conclusions des précédentes "Gewex AtmosphericBoundary Layer Studies" (GABLS) ont conduit au constat que la paramétrisation des couches limites stables dans les modèles climatiques est une des priorités pour la communauté des modélisateurs.Ceci est dû au fait que la nature même des processus physiques en jeu est mal connue mais aussi parce que les lois de similitudes, sur lesquelles les paramétrisations du mélange turbulent sont fondées, ne sont pas applicables en condition très stable. L’objectif de ces travaux de thèse est d’évaluer et d’améliorer la représentation des couches limites sur le plateau antarctique dans le modèle français de circulation générale Laboratoire de MétéorologieDynamique-Zoom (LMDZ), composante atmosphérique du modèle de climat IPSL. Avant l’évaluation même du modèle, une étude approfondie de la couche limite de surface et de la structure de la couche limite stable a été conduite à partir de l’analyse de mesures in situ au Dôme C. Il en a résulté une caractérisation de la hauteur de rugosité aérodynamique, une estimation des flux turbulents de surface sur une année entière ainsi que la mise en évidence de sursaturations de la vapeur d’eau par rapport à la glace. L’analyse des mesures de température et de vent le long d’une tour de 45 m a aussi montré que la couche limite se comporte tel un système dynamique à deux régimes distincts. La relation entrevitesse du vent et inversion de température décrit un "S renversé", suggérant une transition de régime suivant un hystérésis. Une étude complémentaire a révélé que ce comportement dynamique à deux régimes est une caractéristique générale et robuste des couches limites stables, qui peuvent transiter,selon l’intensité des forçages, d’un régime ’turbulent’ peu stable à un régime ’radiatif’ très stable et vice et versa.Le modèle LMDZ a ensuite été évalué en configuration 1D sur un cycle diurne d’été dans le cadre de la quatrième expérience GABLS. Des tests de sensibilité aux paramètres de surface et à la paramétrisation du mélange turbulent ont été réalisés. Ils ont conduit à de nettes améliorations des performancesdu modèle ainsi qu’à la mise en place d’une configuration adaptée aux conditions antarctiques. Des simulations complémentaires en 3D ont par la suite soulevé l’importance du transfert radiatif infrarouge et de la paramétrisation des flux turbulents de surface pour la modélisation de la couchelimite sur le plateau pendant la nuit polaire. Enfin, les travaux de thèse ont été étendus à la modélisation des couches limites stables continentales. Les paramétrisations locales de turbulence ont en effet tendance à sous-estimer le mélange sous-maille continental, en raison de la multitude des processusde mélange en jeu. Un réflexion a donc été portée sur la façon de palier ce manque de mélange, avec comme idée directrice de transférer la perte d’énergie cinétique grande échelle perdue lors du freinage de l’écoulement par les ondes de gravité, vers de l’énergie cinétique turbulente.

International audience; The Coupled Model Intercomparison Project (CMIP) has successfully provided the climate community with a rich collection of simulation output from Earth system models (ESMs) that can be used to understand past climate changes and make projections and uncertainty estimates of the future. Confidence in ESMs can be gained because the models are based on physical principles and reproduce many important aspects of observed climate. More research is required to identify the processes that are most responsible for systematic biases and the magnitude and uncertainty of future projections so that more relevant performance tests can be developed. At the same time, there are many aspects of ESM evaluation that are well established and considered an essential part of systematic evaluation but have been implemented ad hoc with little community coordination. Given the diversity and complexity of ESM analysis, we argue that the CMIP community has reached a critical juncture at which many baseline aspects of model evaluation need to be performed much more efficiently and consistently. Here, we provide a perspective and viewpoint on how a more systematic, open, and rapid performance assessment of the large and diverse number of models that will participate in current and future phases of CMIP can be achieved, and announce our intention to implement such a system for CMIP6. Accomplishing this could also free up valuable resources as many scientists are frequently " re-inventing the wheel " by rewriting analysis routines for well-established analysis methods. A more systematic approach for the community would be to develop and apply evaluation tools that are based on the latest scientific knowledge and observational reference, are well suited for routine use, and provide a wide range of diagnostics and performance metrics that comprehensively characterize model behaviour as soon as the output is published to the Earth System Grid Federation (ESGF). The CMIP infrastructure enforces data standards and conventions for model output and documentation accessible via the ESGF, additionally publishing observations (obs4MIPs) and reanalyses (ana4MIPs) for model Published by Copernicus Publications on behalf of the European Geosciences Union. 814 V. Eyring et al.: Towards improved and more routine Earth system model evaluation in CMIP intercomparison projects using the same data structure and organization as the ESM output. This largely facilitates routine evaluation of the ESMs, but to be able to process the data automatically alongside the ESGF, the infrastructure needs to be extended with processing capabilities at the ESGF data nodes where the evaluation tools can be executed on a routine basis. Efforts are already underway to develop community-based evaluation tools, and we encourage experts to provide additional diagnostic codes that would enhance this capability for CMIP. At the same time, we encourage the community to contribute observations and reanalyses for model evaluation to the obs4MIPs and ana4MIPs archives. The intention is to produce through the ESGF a widely accepted quasi-operational evaluation framework for CMIP6 that would routinely execute a series of standardized evaluation tasks. Over time, as this capability matures, we expect to produce an increasingly systematic characterization of models which, compared with early phases of CMIP, will more quickly and openly identify the strengths and weaknesses of the simulations. This will also reveal whether long-standing model errors remain evident in newer models and will assist modelling groups in improving their models. This framework will be designed to readily incorporate updates, including new observations and additional diagnostics and metrics as they become available from the research community.

International audience; Context and objectives: Evapotranspiration (ET) is a fundamental variable of the hydrological cycle. There is a strong need of methods to monitor ET in space and time, e.g. for evaluating crop water use, improving knowledge in surface processes in hydrological or climate modelling, as well as for weather forecast. We have developed the EVASPA tool to provide continuous mapping of daily ET from remote sensing (RS) data at spatial and temporal scales relevant to hydrological or agronomical studies (Gallego‐Elvira et al., 2013). Further, EVASPA has been designed for providing ET estimations together with estimation uncertainties. In this poster, we provide examples of EVASPA results over the Crau‐Camargue test site (Lower Rhône valley) from MODIS TERRA and AQUA (1km resolution) and LANDSAT‐7 ETM+ data (60 m resolution).

On geological timescales, global climate proxies indicate that variations of large magnitude occur between the Cretaceous and the Cenozoic. On the long term, these variations are mostly determined by the equilibrium between the greenhouse gases composition of the atmosphere, primarily the CO2, and continental weathering set up by the spatial location of Earth’s landmasses. Here, the links between paleogeography and CO2 are looked upon in a climate-ice sheet interactions framework during a greenhouse period of Earth history (120 – 34 Ma). A suite of models involving both coupled and ice sheet models have been used to demonstrate that paleogeographic reorganizations have regulated the presence of ice over Antarctica during the Cretaceous. In a second time and using a similar setup, a new method for climate-ice sheet coupling have been developed and applied to the Eocene-Oligocene (EO) glaciation to yield a new scenario of ice evolution, in good agreement with data. Two feedbacks related to this glaciation and the coeval atmospheric CO2 fall are investigated. First, it is shown that the EO glaciation generates an intensification of the Antarctic Circumpolar Current. Second, within a data-model study demonstrating active Asian monsoons as old as the mid-Eocene, it is shown that the climatic change at the end of the Eocene is responsible for a reduction in the intensity of the Asian monsoon. Finally, with the aim of analysing the effect of paleogeographic changes on marine biogeochemistry during the Cenozoic, sensitivity tests to Drake Passage and Panama Seaway have been carried out.; Les enregistrements climatiques globaux à l’échelle géologique entre le Crétacé et le début du Cénozoïque indiquent des variations de grande amplitude. Sur le long terme, celles-ci sont déterminées par l’équilibre entre la composition atmosphérique en gaz à effet de serre, principalement le CO2, issus du dégazage volcanique et l’altération continentale, modulée par les mouvements tectoniques des continents. Dans cette thèse, les liens entre paléogéographie et CO2 ont été étudiés dans le contexte des interactions entre climat et calottes de glace au cours d’un intervalle de temps dit de « greenhouse », entre 120 et 34 Ma. L’utilisation d’une suite de modèles impliquant un modèle couplé moyenne résolution, un modèle atmosphérique haute résolution et un modèle de calotte de glace, a permis de montrer que les changements paléogéographiques survenant au Crétacé ont régulé la présence de glace en Antarctique. Dans un second temps, une nouvelle méthode de couplage climat-calotte a été développée pour étudier la glaciation Eocène-Oligocène. Ces développements ont permis de reconstruire une évolution fidèle de celle-ci, en bon accord avec les données. Deux rétroactions liées à cette glaciation et à la chute concomitante du CO2 atmosphérique sont étudiées. En premier lieu, l’impact de la glaciation sur le Courant Circumpolaire Antarctique est abordé, montrant que celle-ci génère une intensification de ce courant. Ensuite, au sein d’une étude mêlant données et modèles pour documenter la présence de moussons en Asie dès l’Eocène moyen, il est montré que le changement climatique de la fin de l’Eocène induit une baisse d’intensité de la mousson asiatique. Enfin, dans la perspective d’analyser les conséquences des changements paléogéographiques du Cénozoïque sur la biogéochimie marine, des tests de sensibilité aux passages océaniques de Panama et de Drake ont été réalisés.

International audience; Mithilfe der numerischen Strömungsmechanik (Computational Fluid Dynamics; CFD) untersuchten wir die Ausbreitung von Gasen in und um einen Geflügelstall. Ein 3D- CFD-Modell berücksichtigt die natürliche Belüftung in Kombination mit von den Tieren erzeugten Wärme und Wasserdampf. Um dieses 3-D-CFD-Modell zu validieren, wurden während eines Produktionszyklus in einem Betrieb im Westfrankreichs im Frühjahr 2014 Daten erhoben. Zunächst erfolgte die Überprüfung des dreidimensionalen CFD-Modells auf der Basis des Raumklimas. In der zweiten Stufe sollte die Verteilung der Gase in der Umgebung untersucht werden. Dazu wurde der Wasserdampf räumlich und zeitlich genau im Gebäudeinnenbereich registriert, um die Fahnenentwicklung in der Umgebung des Gebäudes vorherzusagen.; Using Computational Fluid Dynamics (CFD), we investigated the spread of gases inside and around of a poultry house. A 3D CFD model takes account of the natural ventilation combined with heat and water vapour produced by the animals. In order to validate a 3D CFD model a cycle of production for experimental purposes located West of France during the spring, 2014 was used to retrieve data. In the first step, there is a validation of a 3D CFD model based on the interior climate. In the second step, the aim was to identify how the gases might be dispersed in the surrounding environment. Water vapour was accurately logged in space and time for the interior of the building, and then utilized to predict the plume development in the building’s surroundings.

International audience; Um das Raumklima eines Geflügelstalls zu simulieren, wurde ein 2-D-CFD-Modell entwickelt. Für die Validierung des CFD-Modells wurde ein Versuch im Frühjahr 2014 in Westfrankreich durchgeführt. Zwei Versuchsszenarien wurden dabei evaluiert: in der frühen (19. Tag) und der späten (69. Tag) Produktionsstufe. Im Fall II (späte Produktionsstufe) wurden zusätzlich drei unterschiedliche Besatzdichten (33 %, 66 % und 100 % der 10 m-2 untersucht. Das Hauptaugenmerk lag dabei auf dem Verlauf der Temperatur und der Luftfeuchte und demzufolge dem sensiblen und latenten Wärmeverlust. Im Fall I wurden mit dem Modell 10,6 Luftwechsel pro Stunde (± 0,45 Standardabweichung) mit geschätzten 76 % sensiblen bzw. 24 % latenten Wärmeverlusten vorhergesagt. Im Fall II hingegen 25,2 Luftwechsel pro Stunde (± 2,6 Standardabweichung) mit geschätzten 64 % sensiblen bzw. 36 % latenten Wärmeverlusten.; A 2D CFD model was developed to simulate interior climate of a poultry house. To validate the CFD model, an experiment was conducted in West of France during spring 2014. Two cases were evaluated: Case I and II at the early (19th day) and late (69th day) stage of production, respectively. For Case II, the CFD model evaluated three different densities of animals (33 %, 66 % and 100 % of the 10 hens m-2). This work was focused on the temperature and humidity gradients, and then, estimate sensible and latent heat losses. With respect to Case I, the model predicted 10.6 air changes per hour (± 0.45 standard deviation) and also estimated that sensible and latent heat losses of 76 % and 24 %, respectively. With respect to Case II, the model predicted 25.2 air changes per hour (± 2.6 standard deviation) and estimated sensible and latent heat losses approximately of 64 % and 36 %, respectively.

International audience; Mithilfe der numerischen Strömungsmechanik (Computational Fluid Dynamics; CFD) untersuchten wir die Ausbreitung von Gasen in und um einen Geflügelstall. Ein 3D- CFD-Modell berücksichtigt die natürliche Belüftung in Kombination mit von den Tieren erzeugten Wärme und Wasserdampf. Um dieses 3-D-CFD-Modell zu validieren, wurden während eines Produktionszyklus in einem Betrieb im Westfrankreichs im Frühjahr 2014 Daten erhoben. Zunächst erfolgte die Überprüfung des dreidimensionalen CFD-Modells auf der Basis des Raumklimas. In der zweiten Stufe sollte die Verteilung der Gase in der Umgebung untersucht werden. Dazu wurde der Wasserdampf räumlich und zeitlich genau im Gebäudeinnenbereich registriert, um die Fahnenentwicklung in der Umgebung des Gebäudes vorherzusagen.; Using Computational Fluid Dynamics (CFD), we investigated the spread of gases inside and around of a poultry house. A 3D CFD model takes account of the natural ventilation combined with heat and water vapour produced by the animals. In order to validate a 3D CFD model a cycle of production for experimental purposes located West of France during the spring, 2014 was used to retrieve data. In the first step, there is a validation of a 3D CFD model based on the interior climate. In the second step, the aim was to identify how the gases might be dispersed in the surrounding environment. Water vapour was accurately logged in space and time for the interior of the building, and then utilized to predict the plume development in the building’s surroundings.

Understanding the influence of solar variability on the Earth's climate requires knowledge of solar variability, solar-terrestrial interactions and observations, as well as mechanisms determining the response of the Earth's climate system. A summary of our current understanding from observational and modeling studies is presented with special focus on the “top-down” stratospheric UV and the “bottom-up” air-sea coupling mechanisms linking solar forcing and natural climate variability.

High-resolution climate change simulations over the Lesser Antilles are performed using the ALADIN-Climate regional climate model nested within the global model ARPEGE (Météo-France). Three sets of simulations are conducted at 10 km grid spacing for reference (1971–2000) and future climate (2071–2100) under two CMIP5 scenarios (RCP4.5 and RCP8.5). With the dynamical downscaling, islands of Lesser Antilles are considered as land by the model, whereas, for the driving model, there is only sea over the domain. Temperature and precipitation change are analysed on land and on sea separately. For temperature, the warming is greater on land than on sea, especially for the minimum daily temperature (3.2°C vs. 2.3°C for the RCP85 scenario). For precipitation, projections are less reliable because the seasonality is not well reproduced by the model. Nevertheless, simulations exhibit the fact that projections on land differ from one island to the other and disagree with those on sea notably during the wet season. This underlines the importance of the dynamical downscaling to study the climate on small islands. Statistical downscaling has been performed on the Guadeloupe Island to study changes in extreme precipitation indices. The projections provided by the regional climate model suggest an increase in extreme rainfall events: longer dry periods, a bigger annual total precipitation, more frequent very heavy daily precipitation and a stronger 1 d maximum precipitation, whereas for the driving Global Climate Model, these trends are less intense.Keywords: climate change, regional climate model, RCP scenarios, Lesser Antilles, temperature, precipitation(Published: 21 October 2014)Citation: Tellus A 2014, 66, 24065, http://dx.doi.org/10.3402/tellusa.v66.24065

International audience; Le projet CASSANDRE a pour but d'anticiper l'évolution de la végétation dans les Alpes-Maritimes afin d'identifier les zones naturelles à protéger d'ici 2100. La première étape consiste à régionaliser les sorties du modèle climatique ARPEGE-Climat du CNRM afin de renseigner localement l'évolution attendue des températures minimales et maximales à l'horizon de la fin du XXI ème siècle. En croisant des variables prédictives décrivant au mieux l'environnement physique avec les températures en sortie du modèle ARPEGE-Climat, des modèles de régressions multiples sont établis mensuellement pour la période 1961-1990. Les résultats obtenus offrent des résidus acceptables au regard du changement d'échelle opéré (passage de 50 km de résolution à 1 km). Ainsi la même méthode est employée pour affiner la résolution spatiale des modélisations climatiques des Tn et Tx futures (2071-2100) selon les trois scénarios A2, A1B et B1. Mots-clés : Modélisation climatique, descente d'échelle, régression environnementale, température. Abstract: Regionalization of simulated temperatures over France for the period 2071-2100, using the ARPEGE-Climat model and the GES scenarios A1B, A2 and B1. The CASSANDRE project aims at anticipating the vegetation evolution in the Alpes-Maritimes French region to identify natural areas to protect before 2100. The first step consists in regionalizing the outputs of the climate model ARPEGE-Climat of the CNRM to locally evaluate the minimal and maximal temperatures trends at the end of the XXIst century. By crossing predictive variables that best describe the physical environment with temperatures from the ARPEGE-Climat model output, several models of multiple regressions are established monthly for the period 1961-1990. The obtained results give acceptable residues considering the scaling operated (from 50 km horizontal resolution to 1 km). Hence, the same method is used to refine the spatial resolution of the climate model simulated Tn and Tx (2071-2100) according to three SRES scenarios A2, A1B and B1.

The Antarctic Surface Mass Balance (SMB, i.e. the snow accumulation from which we subtract ablation by sublimation, run-off or erosion) is a major yet badly known contribution to changes in the present-day sea level. Water storage by snow accumulation on the Antarctic continent is expected to increase in the 21st century, which would moderate the rise in sea level and impact the ice dynamic response of the ice sheet. Three-quarters of the Antarctic SMB are concentrated below 2000 m above sea level whereas this area represents only 40% of the grounded ice sheet area. Orographic precipitation is a major contributor to snow accumulation in this region, which is why a better estimation of this term is important. The representation of this process by models depends to a great extent on the resolution of the model, since precipitation amounts depend on the ice sheet slopes. Sublimation and snowmelt also depend on elevation, and although they are presently minor contributors to the Antarctic SMB, their role is expected to become more important in the coming centuries. Global and regional atmospheric climate models are unable to achieve a 40-km resolution over Antarctica at a century time scale, due to their computing cost. At this resolution, the Antarctic coastal area is still badly represented. This is why we developed the downscaling model SMHiL (Surface mass balance high-resolution downscaling) to estimate the Antarctic SMB components at a high resolution (~15 km) from large-scale atmospheric forcings. We computed the impact of the high-resolution topography on orographic precipitation amounts and the boundary layer processes that lead to sublimation, melting and refreezing. SMHiL has been validated for the present period with a dataset composed of more than 2700 quality-controlled observations. However, very few of these observations are representative of the Antarctic coastal area. In this context, we show that the GLACIOCLIM-SAMBA stake lines located on the ice sheet coast-to-plateau area is an appropriate reference to evaluate model performance. Finally, we used SMHiL to estimate the SMB changes during the 21st and 22nd centuries, by downscaling the atmospheric global climate model LMDZ4. The high-resolution SMB is significantly different from the SMB given by LMDZ4 and is closer to the observed one for the present period. Our results suggest that previous studies using the LMDZ4 models underestimated the future increase in SMB in Antarctica by about 30%. Future changes in the Antarctic SMB at low elevations will result from the conflict between higher snow accumulation and runoff. The downscaling model is a powerful tool that can be applied to climate models for a better assessment of a future rise in sea level., Le Bilan de Masse de Surface (BMS, c'est-à-dire les précipitations de neige auxquelles est retranchée l'ablation par sublimation, ruissellement ou érosion) de la calotte polaire Antarctique représente une contribution majeure et encore mal connue à l'évolution actuelle du niveau des mers. Le stockage d'eau douce par accumulation de neige sur la calotte posée est supposé s'intensifier au cours du 21eme siècle, modérant l'élévation du niveau des mers et modifiant la dynamique glaciaire. Les trois-quarts du bilan de masse de surface Antarctique sont concentrés au dessous de 2000 m d'altitude alors que cette zone ne représente que 40% de la surface de la calotte posée. Les précipitations orographiques sont une contribution majeure à l'accumulation dans cette région, il est donc crucial d'estimer précisément ce terme. La modélisation de ce processus est fortement dépendant de la résolution des modèles, car les pentes de la calotte influencent l'intensité des précipitations orographiques. La sublimation et la fonte de la neige sont eux aussi fortement dépendant de l'élévation. Bien qu'ils contribuent actuellement peu au bilan de masse de surface de l'Antarctique, ils sont susceptibles de subir des changements importants au cours des prochains siècles. Les modèles atmosphériques de climat, globaux ou régionaux, ne peuvent pas atteindre une résolution allant au delà de 40 km sur l'Antarctique pour des simulations à l'échelle du siècle du fait de coûts de calcul importants. A ces résolutions, la topographie des zones côtières Antarctique n'est pas correctement représentée. C'est pourquoi nous avons développé le modèle de régionalisation SMHiL (Surface Mass balance High-resolution downscaLing) qui permet d'estimer les composantes du bilan de masse de surface Antarctique à haute résolution (~15 km) à partir de champs atmosphériques de plus grande échelle. Nous calculons l'effet de la topographie fine sur les précipitations orographiques et sur les processus de couche limite menant à la sublimation, la fonte et le regel. SMHiL est validé pour la période actuelle à partir d'un jeu de données inédit constitué de plus de 2700 observations de qualité contrôlée. Cependant, les observations représentatives du BMS de la zone côtière Antarctique y sont sous-représentées. Dans ce contexte, nous montrons que la ligne de balise mise en place par l'observatoire GLACIOCLIM-SAMBA en bordure de calotte constitue une référence pour estimer les performances des modèles. Enfin, nous utilisons SMHiL à l'aval du modèle de circulation générale LMDZ4 pour évaluer les variations de BMS au cours du 21eme et du 22eme siècles. Le BMS à haute résolution est significativement différent de celui de LMDZ4 et est plus proche du BMS observé pour la période actuelle. Les résultats suggèrent que les précédentes estimations d'augmentation du BMS au cours du prochain siècle étaient sous-estimées de près de 30% par LMDZ4. Les changements de BMS à faible élévation résulteront d'une compétition entre l'augmentation d'accumulation de neige et de ruissellement. SMHiL est un outil destiné à être appliqué à l'aval d'autres modèles de climat, globaux ou régionaux, pour une meilleure estimation des variations futures du niveau des mers.

Climate modes such as the North Atlantic Oscillation (NAO), representing internal variability of the climate system, influence the ocean carbon cycle and may mask trends in the sink of anthropogenic carbon. Here, utilising control runs of six fully coupled Earth System Models, the response of the ocean carbon cycle to the NAO is quantified. The dominating response, a seesaw pattern between the subtropical gyre and the subpolar Northern Atlantic, is instantaneous (

International audience; This study assesses the accuracy of state-of-the-art regional climate models for agriculture applications in West Africa. A set of nine regional configurations with eight regional models from the ENSEMBLES project is evaluated. Although they are all based on similar large-scale conditions, the performances of regional models in reproducing the most crucial variables for crop production are extremely variable. This therefore leads to a large dispersion in crop yield prediction when using regional models in a climate/crop modelling system. This dispersion comes from the different physics in each regional model and also the choice of parametrizations for a single regional model. Indeed, two configurations of the same regional model are sometimes more distinct than two different regional models. Promising results are obtained when applying a bias correction technique to climate model outputs. Simulated yields with bias corrected climate variables show much more realistic means and standard deviations. However, such a bias correction technique is not able to improve the reproduction of the year-to-year variations of simulated yields. This study confirms the importance of the multi-model approach for quantifying uncertainties for impact studies and also stresses the benefits of combining both regional and statistical downscaling techniques. Finally, it indicates the urgent need to address the main uncertainties in atmospheric processes controlling the monsoon system and to contribute to the evaluation and improvement of climate and weather forecasting models in that respect.

International audience; This work focuses on the Late Saalian (140 ka) Eurasian ice sheets' surface mass balance (SMB) sensitivity to changes in sea surface temperatures (SST). An Atmospheric General Circulation Model (AGCM), forced with two preexisting Last Glacial Maximum (LGM, 21 ka) SST reconstructions, is used to compute climate at 140 and 21 ka (reference glaciation). Contrary to the LGM, the ablation almost stopped at 140 ka due to the climatic cooling effect from the large ice sheet topography. Late Saalian SST are simulated using an AGCM coupled with a mixed layer ocean. Compared to the LGM, these 140 ka SST show an inter-hemispheric asymmetry caused by the larger ice-albedo feedback, cooling climate. The resulting Late Saalian ice sheet SMB is smaller due to the extensive simulated sea ice reducing the precipitation. In conclusion, SST are important for the stability and growth of the Late Saalian Eurasian ice sheet.

International audience; The Regional Atmospheric Modeling System (RAMS) was used to assess local air circulation patterns over the wine-producing Stellenbosch region of South Africa. Numerical simulations using four nested grids (25, 5, and 1 km, and 200 m of horizontal resolution) were performed for each day of February 2000 (during the grape-ripening period) over southern Western Cape Province. Modeled hourly data were extracted from the analysis files and used to produce mean hourly fields (temperature, relative humidity, wind speed, and radiation). Three runs with increasing horizontal resolutions for the finer grid were performed (run 1 with two nested grids of 25 and 5 km; run 2 with three nested grids of 25, 5, and 1 km; run 3 with four nested grids of 25, 5, and 1 km, and 200 m). For each event, the simulations of 1-km and 200-m resolution were superior to the 5-km-resolution simulation, especially in reproducing the local air circulations (sea and slopes breezes) because of a better representation of the local terrain (topography and vegetation cover). The use of a high-resolution grid (200 m) may be of greater value in the identification of potential terrain for viticulture.

Correspondance: alain.migeon@supagro.inra.fr; International audience; Predicting the potential geographical distribution of a species is particularly important for pests with strong invasive abilities. Tetranychus evansi Baker & Pritchard, possibly native to South America, is a spider mite pest of solanaceous crops. This mite is considered an invasive species in Africa and Europe. A CLIMEX model was developed to predict its global distribution. The model results fitted the known records of T. evansi except for some records in dry locations. Dryness as well as excess moisture stresses play important roles in limiting the spread of the mite in the tropics. In North America and Eurasia its potential distribution appears to be essentially limited by cold stress. Detailed potential distribution maps are provided for T. evansi in the Mediterranean Basin and in Japan. These two regions correspond to climatic borders for the species. Mite establishment in these areas can be explained by their relatively mild winters. The Mediterranean region is also the main area where tomato is grown in open fields in Europe and where the pest represents a threat. According to the model, the whole Mediterranean region has the potential to be extensively colonized by the mite. Wide expansion of the mite to new areas in Africa is also predicted. Agricultural issues highlighted by the modelled distribution of the pest are discussed

International audience; Climate is often depicted as globally warm during the middle part of the Cretaceous. However, major tectonic events, such as the break-up of Gondwana, or sea level changes inducing the flooding of vast continental areas, occurred from 120 to 95 Ma resulting in drastic climatic re-organisations. In order to investigate the impact of plate tectonics and sea level change on climate, we performed climatic simulations during the Cenomanian (95 Ma) and Aptian (120 Ma) using an atmospheric general circulation model. Problems with models lie in our knowledge of a few key factors. For examples, the middle Cretaceous sea surface temperature gradient from equator to pole remains an open question and it is not clear yet how flat it was. Two sensitivity experiments for each period prescribing a flatter SST gradient based on oxygen isotopic data have been done in order to test its climatic consequences. We discuss separately the effect of palaeogeography and meridional SST gradient impacts. In the northern hemisphere, the flooding of large continental areas due to sea level rise leads to a more equable climate in the mid-latitudes. However the impact of epicontinental seas varies seasonally from site to site due to local feedbacks. In the southern hemisphere, the breakup of Gondwana deeply affects the climate of this region, moderating the seasonal thermal variations. In addition, we test the impact of a flatter SST gradient on climate and we show that simulations with flat SST gradients compare well with field data. We analyse the remaining model/data discrepancies in terms of missing feedbacks (CO2, vegetation) but also of new measurements that enable to infer a better meridional variation of sea surface temperature.

International audience

International audience

Numerical simulations were performed for 2000-02-03 and 2000-02-04 over the Western Cape in order to observe the alternating sea and land breeze circulation and its effects on diurnal relative humidity and temperature variation, as well as to identify wine-growing areas characterised by high humidity and cool temperature during the maturation period. The Regional Atmospheric Modelling System (RAMS version 4.3) was used at a 1 km resolution. The study domain for the simulation covered a small area from False Bay up to 35 km from the coast. Results are presented using horizontal cross-sections at surface level as well as two south-north cross-sections at longitudes l8°40'E and l8°47'E in order to examine vertical profiles of the atmosphere above the Stellenbosch I Groot Drakenstein winegrowing area. Modelled results agreed with observed data in the vineyards. The sea breeze penetrated at least 35 km inland, but the cooling effect declined rapidly with distance from the sea. Temperature differences between southern and northern slopes near the sea could be significant enough to be important for viticulture.

The semi-Lagrangian atmospheric model on the sphere based on compact finite differences is presented. In the two-dimensional case, the potential vorticity is used as one of the prognostic variables. Fourth-order compact finite differences are used to discretize first- and second-order derivatives. The results including real data tests presented for 2D shallow water version with orography demonstrate its accuracy with the time steps several times greater than in Eulerian model. The 3D version of the model uses the absolute vorticity equation. Some results including a real data forecast are presented. The parallel implementation of the 3D model on a distributed memory parallel computer is described