Intercomparison of oceanic and atmospheric forced and coupled mesoscale simulations <br>Part I: Surface fluxes

International audienceA mesoscale non-hydrostatic atmospheric model has been coupled with a mesoscale oceanic model. The case study is a four-day simulation of a strong storm event observed during the SEMAPHORE experiment over a 500 × 500 km2 domain. This domain encompasses a thermohaline front associated with the Azores current. In order to analyze the effect of mesoscale coupling, three simulations are compared: the first one with the atmospheric model forced by realistic sea surface temperature analyses; the second one with the ocean model forced by atmospheric fields, derived from weather forecast re-analyses; the third one with the models being coupled. For these three simulations the surface fluxes were computed with the same bulk parametrization. All three simulations succeed well in representing the main oceanic or atmospheric features observed during the storm. Comparison of surface fields with in situ observations reveals that the winds of the fine mesh atmospheric model are more realistic than those of the weather forecast re-analyses. The low-level winds simulated with the atmospheric model in the forced and coupled simulations are appreciably stronger than the re-analyzed winds. They also generate stronger fluxes. The coupled simulation has the strongest surface heat fluxes: the difference in the net heat budget with the oceanic forced simulation reaches on average 50 Wm-2 over the simulation period. Sea surface-temperature cooling is too weak in both simulations, but is improved in the coupled run and matches better the cooling observed with drifters. The spatial distributions of sea surface-temperature cooling and surface fluxes are strongly inhomogeneous over the simulation domain. The amplitude of the flux variation is maximum in the coupled run. Moreover the weak correlation between the cooling and heat flux patterns indicates that the surface fluxes are not responsible for the whole cooling and suggests that the response of the ocean mixed layer to the atmosphere is highly non-local and enhanced in the coupled simulation

Mediterranean Sea response to climate change in an ensemble of twenty first century scenarios

The Mediterranean climate is expected to become warmer and drier during the twenty-first century. Mediterranean Sea response to climate change could be modulated by the choice of the socio-economic scenario as well as the choice of the boundary conditions mainly the Atlantic hydrography, the river runoff and the atmospheric fluxes. To assess and quantify the sensitivity of the Mediterranean Sea to the twenty-first century climate change, a set of numerical experiments was carried out with the regional ocean model NEMOMED8 set up for the Mediterranean Sea. The model is forced by air–sea fluxes derived from the regional climate model ARPEGE-Climate at a 50-km horizontal resolution. Historical simulations representing the climate of the period 1961–2000 were run to obtain a reference state. From this baseline, various sensitivity experiments were performed for the period 2001–2099, following different socio-economic scenarios based on the Special Report on Emissions Scenarios. For the A2 scenario, the main three boundary forcings (river runoff, near-Atlantic water hydrography and air–sea fluxes) were changed one by one to better identify the role of each forcing in the way the ocean responds to climate change. In two additional simulations (A1B, B1), the scenario is changed, allowing to quantify the socio-economic uncertainty. Our 6-member scenario simulations display a warming and saltening of the Mediterranean. For the 2070–2099 period compared to 1961–1990, the sea surface temperature anomalies range from +1.73 to +2.97 °C and the SSS anomalies spread from +0.48 to +0.89. In most of the cases, we found that the future Mediterranean thermohaline circulation (MTHC) tends to reach a situation similar to the eastern Mediterranean Transient. However, this response is varying depending on the chosen boundary conditions and socio-economic scenarios. Our numerical experiments suggest that the choice of the near-Atlantic surface water evolution, which is very uncertain in General Circulation Models, has the largest impact on the evolution of the Mediterranean water masses, followed by the choice of the socio-economic scenario. The choice of river runoff and atmospheric forcing both have a smaller impact. The state of the MTHC during the historical period is found to have a large influence on the transfer of surface anomalies toward depth. Besides, subsurface currents are substantially modified in the Ionian Sea and the Balearic region. Finally, the response of thermosteric sea level ranges from +34 to +49 cm (2070–2099 vs. 1961–1990), mainly depending on the Atlantic forcing

Decadal climate variability in the tropical Pacific: Characteristics, causes, predictability, and prospects

This is the author accepted manuscript. The final version is available from the American Association for the Advancement of Science via the DOI in this recordData and materials availability: All observational and model datasets used here are publicly available or available on request.Climate variability in the tropical Pacific affects global climate on a wide range of time scales. On interannual time scales, the tropical Pacific is home to the El Niño–Southern Oscillation (ENSO). Decadal variations and changes in the tropical Pacific, referred to here collectively as tropical Pacific decadal variability (TPDV), also profoundly affect the climate system. Here, we use TPDV to refer to any form of decadal climate variability or change that occurs in the atmosphere, the ocean, and over land within the tropical Pacific. “Decadal,” which we use in a broad sense to encompass multiyear through multidecadal time scales, includes variability about the mean state on decadal time scales, externally forced mean-state changes that unfold on decadal time scales, and decadal variations in the behavior of higher-frequency modes like ENSO

Langage et cerveau : vingt ans d'imagerie fonctionnelle [Language and the brain: 20 years of functional imagery]

La masse considérable de travaux publiés dans le domaine de la neuroimagerie fonctionnelle concernant les fonctions ou modalités du langage (compréhension et expression de la parole, lecture) ou les différents processus linguistiques qui les sous-tendent (sémantique, phonologie, syntaxe) permet de dégager de grandes tendances en termes de substrats anatomiques. Si les « fondamentaux » issus des origines aphasiologiques du domaine n'ont pas été bouleversés, certaines spécificités non explorées par l'approche lésionnelle sont identifiables. Les méta-analyses, en regroupant les résultats de la littérature, nous procurent aujourd'hui une vision globale des substrats cérébraux du langage. Cependant la variabilité inter-individuelle reste importante en raison de multiples facteurs dont certains sont mal identifiés ; cartographier exhaustivement les fonctions du langage à l'échelle individuelle reste une gageure. La quête des images du langage est sans doute aussi inachevable que celle de l'étude du langage lui-même

A simulation of Amazonian deforestation using a GCM calibrated with ABRACOS and ARME data

As parametrizações dos processos de superfície usadas nos MCGA (Modelos de Circulação Geral da Atmosfera) foram bastante aprimoradas na última década, com a inclusão de uma representação explícita da vegetação e dos processos físicos relacionados a ela. No CNRM (Météo-France) um novo esquema, chamado de esquema ISBA (Interações entre Solo, Biosfera e Atmosfera) desenvolvido por Noilhan e Planton (1989), foi implementado no AGCM Espectral EMERAUDE (Manzi e Planton, 1994). Este acoplamento ISBNAGCM é uma ferramenta poderosa para se investigar mudanças de origem natural e antropogênica nas superfícies continentais, como os processos de desertificação ou desmatamento. Neste artigo são apresentados resultados de uma simulação de desmatamento de 4 anos sobre a Amazônia, onde a floresta tropical chuvosa natural e as savanasde uma extensa área da América do Sul foram substituídas por pastagens degradadas. O esquema ISBA foi testado cuidadosamente usando dados dos experimentos observacionais ARME (Experimento Micrometeorológico da Região Amazônica) e ABRACOS, respectivamente, para floresta e pastagem. A simulação com a Amazônia desmatada mostrou um enfraquecimento do ciclo hidrológico e uma amplificação do ciclo diurno da temperatura de superfície quando comparada com a simulação de controle. Um estudo de sensitividade mostrou a grande importância do albedo de superfície e do comportamento da rugosidade na resposta ao desmatamento.Pages: 505-52

Implementation of the ISBA parametrization sheme for land surface processes in a GCM an annual cycle experiment

A parameterization scheme for the Interactions between Soil Biosphere and Atmo- sphere (ISBA), is implemented in the French Spectral General Circulation Model (GCM) Emeraude. ISBA represents surface physical processes including the variability of soil hydrological properties and the influence of vegetation cover on the exchanges between the soil/ cover system and the atmosphere. This paper describes briefiy the scheme and the chosen method to define the parameters at the GCM grid scale. Two annual cycles carried out with and without ISBA are compared with special emphasis given to the simulation of the Amazon Basin region. It is found that the model response to the new scheme is mainly regional, changes at the global scale being explained for the most part by albedo changes. The results over the Amazon forest with the new scheme are in general agreement both with similar numerical experiments performed with other GCM, and with available data set collected in this region. The impact of the scheme on the simulated surface fields also point out some interaction mechanisms associating surface processes, convection, and radiation through the representation of convective cloudiness. The characteristic times of the soil moisture initialization are also examined according to the variability of soil and vegetation types. It is found that the most rapid adjustment time is mainly textural dependent as the response time related to the water transfer into the soil is mainly dependent on moisture conditions. Vegetation cover also introduces a lag time in the adjustment process due to the interception of precipitation.Pages: 1-3

Climatic impact os tropical deforestation simulations

Two Amazonian deforestation simulation experimenta have been performed with the French spectral GCM EMERAUDE coupled wlth the ISBA land surface parameterisations of Noilhan and Planton (1989). The deep convection scheme ot Bouqeault (1985) was used in the first experiment while the Ruo scheme (1965, 1974), includinq the modifications of Geleyn (1985), was used in the second one. For each experiment the model was inteqrated with the original soil and veqetation types from the classification of Wilson and Henderson-Sellers (1985) in the contraI case (ctrl). In the deforested case (def) a hypothetical qrass land cover replaced the rainforest over a larqe surface over the Amazonian reqion. The main ISBA parameters for forest and qrass land are respectively: albedo 12.5t and 19ti rouqhness lenqth 2 m and 6 cmi active soil column depth 4 m and 2 mi and minimum surface resistance 42 sim and 75 sim. The initial soil water content used are that from Mintz and Seratini (1989) climatoloqy for a mid-Cecember situation. The precipitation pattern obtained with the Kuo scheme seems in better aqreement with the climatoloqy over the South America continent than that obtained with the Bouqeault one. Over the deforested reqion the precipitation decreases, followinq the decreased evapotranspiration, when the Kuo scheme is used while the humidity converqence, of about 50t of precipitation, remains unchanqed. An increase of precipitation resulta from the deforestation when the Bouqeault scheme is used as a consequence of the increased humidity converqence. The impact ot the increased albedo is compensated by a decreased cloudiness in both simulations. The resulted averaqed surface temperatura remains almost unchanqed, althouqh the daily temperature amplitude is larqer in the def experimento This increased daily temperatura amplitude may be explained by the decreased rouqhness lenqth. An increased runoff resulta from the lower soil water capacity.Pages: 37