23 research outputs found
LMDZ5B: the atmospheric component of the IPSL climate model with revisited parameterizations for clouds and convection
Influence de l'hydrologie souterraine sur la modélisation du climat à l'échelle régionale et globale
Les ModĂšles de Circulation GĂ©nĂ©rale (MCG) sont des outils permettant l'Ă©tude du climat Ă grande Ă©chelle et de ses principales tendances. Les bilans d'eau et d'Ă©nergie Ă la surface des continents y sont calculĂ©s Ă l'aide de modĂšle de surface continentale (Land Surface Model, LSM). Ces derniĂšres annĂ©es, l'intĂ©rĂȘt d'utiliser un LSM sophistiquĂ© pour modĂ©liser le climat terrestre s'est affirmĂ©, notamment au niveau des rĂ©gions tempĂ©rĂ©es qui abritent des zones de transition oĂč l'Ă©vapotranspiration est limitĂ©e d'une part par l'Ă©nergie d'autre part par l eau disponible. Le site instrumentĂ© du SIRTA mesure de nombreuses variables atmosphĂ©riques permettant de valider un modĂšle climatique en un point. Le SIRTA dispose Ă©galement de donnĂ©es d'humiditĂ© du sol utilisĂ©es pour la premiĂšre fois dans cette thĂšse. Ces donnĂ©es rĂ©vĂšlent la prĂ©sence d'une nappe perchĂ©e, en accord avec une campagne de mesures gĂ©ophysiques rĂ©alisĂ©e durant cette thĂšse. Les donnĂ©es du SIRTA sont confrontĂ©es Ă des simulations rĂ©gionales qui sont rĂ©alisĂ©es Ă l'aide du LSM ORCHIDEE couplĂ© Ă un modĂšle atmosphĂ©rique. Nous dĂ©veloppons la possibilitĂ© d'imposer une nappe au sein du sol modĂ©lisĂ© par ORCHIDEE, ce qui permet de soutenir l'Ă©vaporation en Ă©tĂ© au SIRTA, en accord avec les observations. Nous explorons diffĂ©rentes hypothĂšses hydrologiques qui entrainent une augmentation de l'Ă©vaporation Ă l'Ă©chelle de l'Europe de l'Ouest et impliquent une augmentation des prĂ©cipitations ainsi qu un refroidissement de l'air. Ces hypothĂšses sont Ă©galement testĂ©es lors de simulations globales afin d'en Ă©tudier l'influence sur les caractĂ©ristiques du climat et du changement climatique causĂ© par une augmentation de gaz Ă effet de serre.General Circulation Models (GCM) are tools which allow studying climate at large scale. Water and energy budget over continental surface are calculated by Land Surface Model (LSM). Interest on using a sophistical LSM to simulate earth climate grew up last years, in particular in transition area, where evaporation is limited on one side by energy and on other side by available water. The instrumented site of SIRTA observes many atmospheric variables and allows validating a climate model on one point. The SIRTA have also soil moisture data which are used for the first time in this thesis. These data reveal a shallow water table, according to geophysical campaign conducted during this thesis. Data from SIRTA are confronted to regional simulations produced with the LSM ORCHIDEE coupled to an atmospheric model. We develop the possibility to impose a water table in the soil modeled by ORCHIDEE, which allows maintaining evaporation during summer at the SIRTA, according to observations. We explore different hydrologic hypothesis which conduct to an evaporation increase at Western European scale and also involve precipitation increase and air cooling. Theses hypothesis are also tested in global simulations to study effects on climate and on climate change due to an increase of greenhouse gases.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF
A density current parameterization coupled with Emanuel's convection scheme. Part II: 1D simulations
International audienceThe density current parameterization coupled with Emanuel's convection scheme, described in Part I of this series of papers, is tested in a single-column framework for continental and maritime convective systems. The case definitions and reference simulations are provided by cloud-resolving models (CRMs). For both cases, the wake scheme yields cold pools with temperature and humidity differences relative to the environment in reasonable agreement with observations (with wake depth on the order of 2 km over land and 1 km over ocean). The coupling with the convection scheme yields convective heating, drying, and precipitation similar to those simulated by the CRM. Thus, the representation of the action of the wakes on convection in terms of available lifting energy (ALE) and available lifting power (ALP) appears satisfactory. The sensitivity of the wake-convection system to the basic parameters of the parameterization is widely explored. A range of values for each parameter is recommended to help with implementing the scheme in a full-fledged general circulation model. © 2010 American Meteorological Society
Improving climate model skill over High Mountain Asia by adapting snow cover parameterization to complex-topography areas
Abstract. This study investigates the impact of topography on five snow cover fraction (SCF) parameterizations developed for global climate models (GCMs), including two novel ones. The parameterization skill is first assessed with the High Mountain Asia Snow Reanalysis (HMASR), and three of them are implemented in the ORCHIDEE land surface model (LSM) and tested in global landâatmosphere coupled simulations. HMASR includes snow depth (SD) uncertainties, which may be due to the elevation differences between in situ stations and HMASR grid cells. Nevertheless, the SCFâSD relationship varies greatly between mountainous and flat areas in HMASR, especially during the snow-melting period. The new parameterizations that include a dependency on the subgrid topography allow a significant SCF bias reduction, reaching 5â% to 10â% on average in the global simulations over mountainous areas, which in turn leads to a reduction of the surface cold bias from â1.8ââC to about â1ââC in High Mountain Asia (HMA). Furthermore, the seasonal hysteresis between SCF and SD found in HMASR is better captured in the parameterizations that split the accumulation and the depletion curves or that include a dependency on the snow density. The deep-learning SCF parameterization is promising but exhibits more resolution-dependent and region-dependent features. Persistent snow cover biases remain in global landâatmosphere experiments. This suggests that other model biases may be intertwined with the snow biases and points out the need to continue improving snow models and their calibration. Increasing the model resolution does not consistently reduce the simulated SCF biases, although biases get narrower around mountain areas. This study highlights the complexity of calibrating SCF parameterizations since they affect various landâatmosphere feedbacks. In summary, this research spots the importance of considering topography in SCF parameterizations and the challenges in accurately representing snow cover in mountainous regions. It calls for further efforts to improve the representation of subgrid-scale processes affecting snowpack in climate models
Impact of a shallow groundwater table on the global water cycle in the IPSL landâatmosphere coupled model
International audienceThe main objective of the present work is to study the impacts of water table depth on the near surface climate and the physical mechanisms responsible for these impacts through the analysis of landâatmosphere coupled numerical simulations. The analysis is performed with the LMDZ (standard physics) and ORCHIDEE models, which are the atmosphere-land components of the Institut Pierre Simon Laplace (IPSL) Climate Model. The results of sensitivity experiments with groundwater tables (WT) prescribed at depths of 1 m (WTD1) and 2 m (WTD2) are compared to the results of a reference simulation with free drainage from an unsaturated 2 m soil (REF). The response of the atmosphere to the prescribed WT is mostly concentrated over land, and the largest differences in precipitation and evaporation are found between REF and WTD1. Saturating the bottom half of the soil in WTD1 induces a systematic increase of soil moisture across the continents. Evapotranspiration (ET) increases over water-limited regimes due to increased soil moisture, but it decreases over energy-limited regimes due to the decrease in downwelling radiation and the increase in cloud cover. The tropical (25°Sâ25°N) and mid-latitude areas (25°Nâ60°N and 25°Sâ60°S) are significantly impacted by the WT, showing a decrease in air temperature (â0.5 K over mid-latitudes and â1 K over tropics) and an increase in precipitation. The latter can be explained by more vigorous updrafts due to an increased meridional temperature gradient between the equator and higher latitudes, which transports more water vapour upward, causing a positive precipitation change in the ascending branch. Over the West African Monsoon and Australian Monsoon regions, the precipitation changes in both intensity (increases) and location (poleward). The more intense convection and the change of the large-scale dynamics are responsible for this change. Transition zones, such as the Mediterranean area and central North America, are also impacted, with strengthened convection resulting from increased ET
Une méthode utilisant les techniques neuronales pour le calcul rapide de la distribution verticale du bilan radiatif thermique terrestre.
International audienc
SynthĂšse de 10 ans d'observation de l'atmosphĂšre au SIRTA : utilisation pour l'Ă©valuation des modĂšles de climat dans le cadre d'EUCLIPSE
Le SIRTA (Site InstrumentĂ© de Recherche par TĂ©lĂ©dĂ©tection AtmosphĂ©rique, en Ile de France) dispose d'une multitude de donnĂ©es depuis 2002 : mesure des champs thermodynamiques, mesures de flux radiatifs, mesures par lidar, mesure par radiomĂ©trie... Il est donc possible de documenter l'ensemble de la colonne atmosphĂ©rique et donc les variables ayant une sensibilitĂ© climatique importante, Ă l'Ă©chelle dĂ©cennale. Jusqu'Ă ce jour, la synergie entre les diffĂ©rents capteurs est sous-utilisĂ©e, il y a une grande hĂ©tĂ©rogĂ©nĂ©itĂ© de formats de fichier, de rĂ©solution temporelle, de niveau de contrĂŽle qualitĂ©, de documentation : cette grande base de donnĂ©es est donc difficile Ă utiliser pour des analyses statistiques, et pour des chercheurs non spĂ©cialistes de la mesure. Depuis plus d'un an, nous travaillons Ă l'Ă©laboration d'un fichier unique (netcdf) contenant toutes ces donnĂ©es, homogĂ©nĂ©isĂ©es en termes de rĂ©solution (moyennes horaires), avec une attention particuliĂšre mise sur le contrĂŽle qualitĂ©. Des variables comme la fraction nuageuse ou la vapeur d'eau qui peuvent ĂȘtre restituĂ©es Ă partir de plusieurs instruments font l'objet d'Ă©tudes particuliĂšres pour dĂ©duire une variable unique associĂ©e Ă une barre d'erreur. A partir de ces donnĂ©es, les variables dĂ©finies par CFMIP sont extraites pour les deux annĂ©es identifiĂ©es par EUCLIPSE, afin de construire un deuxiĂšme fichier plus spĂ©cifique Ă ce projet europĂ©en, et dans lequel la nomenclature sera celle de CFMIP. Un fichier Ă©quivalent est Ă©galement construit pour l'observatoire hollandais de Cabaw. Ces synthĂšses sont et seront utilisĂ©es aussi bien pour des analyses purement observationnelles, que pour des Ă©tudes portant sur l'Ă©valuation des modĂšles et de leurs paramĂ©trisations
Influence historique de l'irrigation dans le bassin de la Seine
Irrigation aims to increase and stabilize agricultural yields, particularly in the face of droughts, which are expected to intensify as a result of global warming. However, the scientific literature shows that, while irrigation reduces agronomic droughts, it increases hydrological droughts. In order to specify the potential impacts of irrigation on the hydrology and regional climate of the Seine basin, we firstly relied on observations without being able to highlight any obvious relationship. We hope to deepen this analysis thanks to modelling, which allows us to compare situations with and without irrigation, all other things being equal. This approach is illustrated using global climate simulations carried out for the sixth IPCC report. The description of irrigation that has just been implemented in the ORCHIDEE model thus offers numerous perspectives, including the assessment of the future evolution of the Seine river basin.L'irrigation vise Ă augmenter et stabiliser les rendements agricoles, notamment face aux sĂ©cheresses, dont on attend l'intensification sous l'effet du rĂ©chauffement climatique. La littĂ©rature scientifique montre cependant que, si l'irrigation rĂ©duit les sĂ©cheresses agronomiques, elle augmente les sĂ©cheresses hydrologiques. Pour prĂ©ciser les impacts potentiels de l'irrigation sur l'hydrologie et le climat rĂ©gional du bassin de la Seine, nous nous sommes d'abord appuyĂ©s sur des observations sans pouvoir mettre en Ă©vidence de relation Ă©vidente. Nous espĂ©rons pouvoir approfondir cette analyse grĂące Ă la modĂ©lisation, qui permet de comparer des situations avec et sans irrigation, toutes choses par ailleurs. Cette dĂ©marche est illustrĂ©e Ă partir de simulations climatiques globales rĂ©alisĂ©es pour le sixiĂšme rapport du GIEC. La description de l'irrigation qui vient d'ĂȘtre implĂ©mentĂ©e dans le modĂšle ORCHIDEE offre ainsi de nombreuses perspectives, y compris pour aborder l'Ă©volution future de l'hydrosystĂšme Seine. Points clefs â Les surfaces irriguĂ©es ont Ă©tĂ© multipliĂ©es par 4 depuis 1970 dans le bassin de la Seine, et par 3 sur la seule dĂ©cennie 1970-1980 â Pas de tendance robuste des dĂ©bits observĂ©s tout au long de la pĂ©riode 1979-2021 malgrĂ© une faible augmentation de l'Ă©vapotranspiration â Le modĂšle ORCHIDEE permet de dĂ©crire l'irrigation et son influence sur les ressources en eau mais il doit ĂȘtre mieux validĂ© dans le bassin de la Sein
Influence historique de l'irrigation dans le bassin de la Seine
Irrigation aims to increase and stabilize agricultural yields, particularly in the face of droughts, which are expected to intensify as a result of global warming. However, the scientific literature shows that, while irrigation reduces agronomic droughts, it increases hydrological droughts. In order to specify the potential impacts of irrigation on the hydrology and regional climate of the Seine basin, we firstly relied on observations without being able to highlight any obvious relationship. We hope to deepen this analysis thanks to modelling, which allows us to compare situations with and without irrigation, all other things being equal. This approach is illustrated using global climate simulations carried out for the sixth IPCC report. The description of irrigation that has just been implemented in the ORCHIDEE model thus offers numerous perspectives, including the assessment of the future evolution of the Seine river basin.L'irrigation vise Ă augmenter et stabiliser les rendements agricoles, notamment face aux sĂ©cheresses, dont on attend l'intensification sous l'effet du rĂ©chauffement climatique. La littĂ©rature scientifique montre cependant que, si l'irrigation rĂ©duit les sĂ©cheresses agronomiques, elle augmente les sĂ©cheresses hydrologiques. Pour prĂ©ciser les impacts potentiels de l'irrigation sur l'hydrologie et le climat rĂ©gional du bassin de la Seine, nous nous sommes d'abord appuyĂ©s sur des observations sans pouvoir mettre en Ă©vidence de relation Ă©vidente. Nous espĂ©rons pouvoir approfondir cette analyse grĂące Ă la modĂ©lisation, qui permet de comparer des situations avec et sans irrigation, toutes choses par ailleurs. Cette dĂ©marche est illustrĂ©e Ă partir de simulations climatiques globales rĂ©alisĂ©es pour le sixiĂšme rapport du GIEC. La description de l'irrigation qui vient d'ĂȘtre implĂ©mentĂ©e dans le modĂšle ORCHIDEE offre ainsi de nombreuses perspectives, y compris pour aborder l'Ă©volution future de l'hydrosystĂšme Seine. Points clefs â Les surfaces irriguĂ©es ont Ă©tĂ© multipliĂ©es par 4 depuis 1970 dans le bassin de la Seine, et par 3 sur la seule dĂ©cennie 1970-1980 â Pas de tendance robuste des dĂ©bits observĂ©s tout au long de la pĂ©riode 1979-2021 malgrĂ© une faible augmentation de l'Ă©vapotranspiration â Le modĂšle ORCHIDEE permet de dĂ©crire l'irrigation et son influence sur les ressources en eau mais il doit ĂȘtre mieux validĂ© dans le bassin de la Sein
Influence historique de l'irrigation dans le bassin de la Seine
Irrigation aims to increase and stabilize agricultural yields, particularly in the face of droughts, which are expected to intensify as a result of global warming. However, the scientific literature shows that, while irrigation reduces agronomic droughts, it increases hydrological droughts. In order to specify the potential impacts of irrigation on the hydrology and regional climate of the Seine basin, we firstly relied on observations without being able to highlight any obvious relationship. We hope to deepen this analysis thanks to modelling, which allows us to compare situations with and without irrigation, all other things being equal. This approach is illustrated using global climate simulations carried out for the sixth IPCC report. The description of irrigation that has just been implemented in the ORCHIDEE model thus offers numerous perspectives, including the assessment of the future evolution of the Seine river basin.L'irrigation vise Ă augmenter et stabiliser les rendements agricoles, notamment face aux sĂ©cheresses, dont on attend l'intensification sous l'effet du rĂ©chauffement climatique. La littĂ©rature scientifique montre cependant que, si l'irrigation rĂ©duit les sĂ©cheresses agronomiques, elle augmente les sĂ©cheresses hydrologiques. Pour prĂ©ciser les impacts potentiels de l'irrigation sur l'hydrologie et le climat rĂ©gional du bassin de la Seine, nous nous sommes d'abord appuyĂ©s sur des observations sans pouvoir mettre en Ă©vidence de relation Ă©vidente. Nous espĂ©rons pouvoir approfondir cette analyse grĂące Ă la modĂ©lisation, qui permet de comparer des situations avec et sans irrigation, toutes choses par ailleurs. Cette dĂ©marche est illustrĂ©e Ă partir de simulations climatiques globales rĂ©alisĂ©es pour le sixiĂšme rapport du GIEC. La description de l'irrigation qui vient d'ĂȘtre implĂ©mentĂ©e dans le modĂšle ORCHIDEE offre ainsi de nombreuses perspectives, y compris pour aborder l'Ă©volution future de l'hydrosystĂšme Seine. Points clefs â Les surfaces irriguĂ©es ont Ă©tĂ© multipliĂ©es par 4 depuis 1970 dans le bassin de la Seine, et par 3 sur la seule dĂ©cennie 1970-1980 â Pas de tendance robuste des dĂ©bits observĂ©s tout au long de la pĂ©riode 1979-2021 malgrĂ© une faible augmentation de l'Ă©vapotranspiration â Le modĂšle ORCHIDEE permet de dĂ©crire l'irrigation et son influence sur les ressources en eau mais il doit ĂȘtre mieux validĂ© dans le bassin de la Sein