CMIP5 Model Intercomparison of Freshwater Budget and Circulation in the North Atlantic

ABSTRACT The subpolar North Atlantic is a center of variability of ocean properties, wind stress curl, and air–sea exchanges. Observations and hindcast simulations suggest that from the early 1970s to the mid-1990s the subpolar gyre became fresher while the gyre and meridional circulations intensified. This is opposite to the relationship of freshening causing a weakened circulation, most often reproduced by climate models. The authors hypothesize that both these configurations exist but dominate on different time scales: a fresher subpolar gyre when the circulation is more intense, at interannual frequencies (configuration A), and a saltier subpolar gyre when the circulation is more intense, at longer periods (configuration B). Rather than going into the detail of the mechanisms sustaining each configuration, the authors’ objective is to identify which configuration dominates and to test whether this depends on frequency, in preindustrial control runs of five climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). To this end, the authors have developed a novel intercomparison method that enables analysis of freshwater budget and circulation changes in a physical perspective that overcomes model specificities. Lag correlations and a cross-spectral analysis between freshwater content changes and circulation indices validate the authors’ hypothesis, as configuration A is only visible at interannual frequencies while configuration B is mostly visible at decadal and longer periods, suggesting that the driving role of salinity on the circulation depends on frequency. Overall, this analysis underscores the large differences among state-of-the-art climate models in their representations of the North Atlantic freshwater budget

Influence de la formation d'eau profonde sur la variabilité de la circulation méridienne moyenne dans l'Océan Atlantique

The oceanic meridional overturning circulation (MOC) and the associated poleward heat transport contribute substantially to the energy balance of present climate. One fundamental driver of the MOC is deep water formation in the North Atlantic. The objective of this study is to investigate the influence of changes in the rate of deep water formation on the variability of the MOC in the Atlantic Ocean.First, we develop an analytic model to investigate the spectral characteristics of the response of the MOC to changes in the rate of deep water formation in the North Atlantic. This simple theoretical model reproduces qualitatively few characteristics of the variability of the MOC observed in climate models.Then a realistic simulation of the circulation in the North Atlantic from 1953 to 2003 is used to determine the mechanisms of variability associated with the formation and export of deep water in the subpolar North Atlantic. These mechanisms, which are consistent with observations, help to understand the link between changes in the rate of deep water formation and the variability of the transport in the Deep Western Boundary Current, which constitutes the deep limb of the MOC in the North Atlantic. Finally we investigate the influence of these mechanisms on the circulation in the North Atlantic. We show that the interannual to multidecadal variability of the MOC can be considered as an integration of the rate of deep water formation in the Irminger Sea.La stabilité du climat actuel est assurée par le transport méridien de chaleur de l’équateur vers les pôles, auquel contribue significativement la circulation océanique méridienne moyenne (MOC), qui transporte des masses d’eau denses formées dans l’AtlantiqueNord et l’Océan Antarctique en profondeur vers l’équateur. L’objet de cette thèse est de comprendre l’influence de la variabilité du taux de formation d’eau profonde dans l’Atlantique Nord sur la variabilité interannuelle à multi décennale de la MOC.Dans la première partie de la thèse, un modèle analytique est développé pour étudier les caractéristiques spectrales de la variabilité de la MOC forcée par des fluctuations du taux de formation d’eau profonde dans l’Atlantique Nord. Ce modèle simple reproduit qualitativement certaines caractéristiques spectrales de la MOC observées dans les modèles de climat.Une simulation réaliste de la circulation dans l’Atlantique Nord de 1953 à 2003 est ensuite étudiée, pour déterminer les mécanismes de variabilité de la formation et de l’exportation d’eau profonde dans la gyre subpolaire. Ces mécanismes, qui ont été suggérés par les observations, permettent de comprendre le lien entre la variabilité de la formation d’eau profonde dans la gyre subpolaire et la variabilité du transport dans le courant profond de bord ouest, qui constitue l’essentiel de la branche profonde de la MOC dans l’Atlantique Nord. On étudie enfin leur influence sur la circulation dans l’Atlantique Nord. On montre notamment que la variabilité interannuelle à multidécennale de la MOC peut être considérée comme l’intégration des fluctuations du taux de formation d’eau profonde dans la mer d’Irminger

Mechanisms of variability in a convective basin

Author Posting. © Sears Foundation for Marine Research, 2009. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 67 (2009): 273-303, doi:10.1357/002224009789954757.An idealized model for a convective basin is used to investigate the mechanisms of variability of the formation and export of dense water. In this model, which consists of two isopycnic layers, dense water formation is induced by surface buoyancy loss in the interior, which is at rest. Newly formed dense water is transmitted to the surrounding boundary current through parameterized eddy fluxes. Variability in the formation and export of dense water is due to changes in the two main drivers: variations in the surface buoyancy fluxes and variations in the large-scale wind via a barotropic boundary current. Numerical integrations of the nonlinear model, with parameters and forcings corresponding to the Labrador Sea, show that the rate of dense water formation in the interior of the basin is strongly affected by changes in the buoyancy forcing, but not significantly affected by seasonal to interannual changes in the wind-driven barotropic boundary current. The basin tends to integrate the buoyancy forcing variability with a memory time scale set by eddies, which is decadal for the Labrador Sea. Variability in dense water export, on the contrary, is strongly affected by changes in the wind-driven barotropic boundary current but hardly affected by changes in buoyancy forcing. Indeed changes in the transport of dense water at the basin outflow are dominated by those at the basin inflow, which, in this model, are directly related to fluctuations in the wind-driven barotropic boundary current. These results, which are consistent with analytical solutions of the linear model, suggest that fluctuations in the surface buoyancy fluxes in the interior Labrador Sea have little impact on the interannual variability of the dense water transport by the Deep Western Boundary Current at the outflow of the Labrador Sea, which is dominated by fluctuations in the wind-driven North Atlantic subpolar gyre, but influence the formation and export of recently ventilated waters.Support for JD from the NOAA Office of Hydrologic Development through a scientific appointment administered by UCAR is gratefully acknowledged. Support for FS was provided by NSF grant OCE−0525929. Support for MAS was provided by NSF grant OCE−0423975

« C’est déjà les parents qu’il faudrait éduquer ! »

L’observation ethnographique d’entretiens enseignante-parents (n = 150), dans ces écoles du canton de Genève, renseigne sur les pratiques vernaculaires des enseignantes relevant d’une éducation des parents. Celle-ci, propice aux tâtonnements, se réalise toutefois de manière implicite et s’avère dotée de faibles ressources. Dans ce texte, nous analysons comment les enseignantes s’y prennent pour agir, quelles tactiques elles mettent en œuvre et quelles postures variées sont construites dans la relation de conseil aux parents. Il s’agit d’en montrer les effets sur la communication interindividuelle dans l’entretien et sur la réception variée des parents, laquelle tient à leurs propres attentes, à la situation scolaire de leur enfant, à leurs ressources pour faire face à ces difficultés, mais aussi aux capacités, elles-mêmes diverses, des enseignantes à agir avec tact sur un terrain éminemment sensible.In schools located in socially underprivileged areas, more than anywhere else, the necessity to educate parents constitutes a constant in the behind-the-scenes relationship with the teachers. The ethnographic observation of teacher-parent meetings (n =150) in this schools in the canton of Geneva give insight into the teachers’ vernacular practices aiming to educate parents. However, this practice is undertaken in implicit manner, supported by few resources and often reduced to trial and error. In this text, we will analyze how teachers take action, the tactics they use and the various positions they adopt in the guidance they give to parents. We will show the resulting effects on the interindividual communication in the meetings and on the parents’ reactions, which reflect their own expectations, the situation of their child in school, the resources available to them to deal with the child’s difficulties, as well as the often-diverse capabilities of the teachers to act with tact in a highly sensitive context.En las escuelas situadas en contextos sociales desfavorecidos, la necesidad de «educar a los padres» constituye, más que en otros lugares, una constante de los entresijos educativos. La observación etnográfica de las entrevistas entre padres y docentes (n = 150) en estas escuelas del cantón de Ginebra, nos informa sobre las prácticas vernáculas de los docentes derivadas de una educación de los padres. No obstante, todo lo anterior, propicio al tanteo, se realiza de manera implícita y su dotación de recursos se revela escasa. En este texto, analizamos cómo los docentes se las arreglan para actuar, qué tácticas adoptan y qué posturas diferentes se construyen en la relación de asesoramiento a los padres. Se trata de mostrar los efectos sobre la comunicación interindividual en la entrevista y sobre la variedad de reacciones por parte de los padres, la cual depende de sus propias expectativas, de la situación escolar del menor, de sus recursos para hacer frente a estas dificultades, pero también de las capacidades, también diversas, de los docentes para actuar con tacto sobre un terreno eminentemente sensible

Bueil – Le Pelleret, rue du Puits

Dans le cadre de travaux de pose d’une nouvelle conduite d’assainissement entre Bueil et le hameau de Chanu (commune de Villiers-en-Desœuvre), l’entreprise EHTP a fait la découverte de trois sépultures. Suite à un arrêt de chantier, une opération de fouille urgente consécutive à cette découverte fortuite a pu être engagée. Seine-Normandie-Agglomération, maître d’ouvrage des travaux, a accepté de prendre en charge le financement de l’intervention. Des sondages ponctuels ont été réalisés sur le..

The role of salinity in the decadal variability of the North Atlantic meridional overturning circulation

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Climate Dynamics 33 (2009): 777-793, doi:10.1007/s00382-008-0523-2.An OGCM hindcast is used to investigate the linkages between North Atlantic Ocean salinity and circulation changes during 1963–2003. The focus is on the eastern subpolar region consisting of the Irminger Sea and the eastern North Atlantic where a careful assessment shows that the simulated interannual to decadal salinity changes in the upper 1500 m reproduce well those derived from the available record of hydrographic measurements. In the model, the variability of the Atlantic meridional overturning circulation (MOC) is primarily driven by changes in deep water formation taking place in the Irminger Sea and, to a lesser extent, the Labrador Sea. Both are strongly influenced by the North Atlantic Oscillation (NAO). The modeled interannual to decadal salinity changes in the subpolar basins are mostly controlled by circulation-driven anomalies of freshwater flux convergence, although surface salinity restoring to climatology and other boundary fluxes each account for approximately 25% of the variance. The NAO plays an important role: a positive NAO phase is associated with increased precipitation, reduced northward salt transport by the wind-driven intergyre gyre, and increased southward flows of freshwater across the Greenland-Scotland ridge. Since the NAO largely controlled deep convection in the subpolar gyre, fresher waters are found near the sinking region during convective events. This markedly differs from the active influence on the MOC that salinity exerts at decadal and longer timescales in most coupled models. The intensification of the MOC that follows a positive NAO phase by about 2 years does not lead to an increase in the northward salt transport into the subpolar domain at low frequencies because it is cancelled by the concomitant intensification of the subpolar gyre which shifts the subpolar front eastward and reduces the northward salt transport by the North Atlantic Current waters. This differs again from most coupled models, where the gyre intensification precedes that of the MOC by several years.Support from NSF Grant 82677800 with the Woods Hole Oceanographic Institution, and (to CF) from the Institut universitaire de France and European FP6 project DYNAMITE (contract 003903-GOCE) and (to JD) from the NOAA Office of Hydrologic Development through a scientific appointment administered by UCAR is gratefully acknowledged

Preindustrial control simulations with HadGEM3-GC3.1 for CMIP6

Pre‐industrial control simulations with the HadGEM3‐GC3.1 climate model are presented at two resolutions. These are N216ORCA025, which has a horizontal resolution of 60km in the atmosphere and 0.25° in the ocean, and N96ORCA1, which has a horizontal resolution of 130km in the atmosphere and 1° in the ocean. The aim of this study is to document the climate variability in these simulations, make comparisons against present‐day observations (albeit under different forcing), and discuss differences arising due to resolution. In terms of interannual variability in the leading modes of climate variability the two resolutions behave generally very similarly. Notable differences are in the westward extent of El‐Niño and the pattern of Atlantic multidecadal variability, in which N216ORCA025 compares more favourably to observations, and in the Antarctic Circumpolar Current, which is far too weak in N216ORCA025. In the North Atlantic region, N216ORCA025 has a stronger and deeper AMOC, which compares well against observations, and reduced biases in temperature and salinity in the North Atlantic subpolar gyre (NA SPG). These simulations are being provided to the sixth Coupled Model Intercomparison Project (CMIP6) and provide a baseline against which further forced experiments may be assessed

OMIP contribution to CMIP6: experimental and diagnostic protocol for the physical component of the Ocean Model Intercomparison Project

The Ocean Model Intercomparison Project (OMIP) is an endorsed project in the Coupled Model Intercomparison Project Phase 6 (CMIP6). OMIP addresses CMIP6 science questions, investigating the origins and consequences of systematic model biases. It does so by providing a framework for evaluating (including assessment of systematic biases), understanding, and improving ocean, sea-ice, tracer, and biogeochemical components of climate and earth system models contributing to CMIP6. Among the WCRP Grand Challenges in climate science (GCs), OMIP primarily contributes to the regional sea level change and near-term (climate/decadal) prediction GCs. OMIP provides (a) an experimental protocol for global ocean/sea-ice models run with a prescribed atmospheric forcing; and (b) a protocol for ocean diagnostics to be saved as part of CMIP6. We focus here on the physical component of OMIP, with a companion paper (Orr et al., 2016) detailing methods for the inert chemistry and interactive biogeochemistry. The physical portion of the OMIP experimental protocol follows the interannual Coordinated Ocean-ice Reference Experiments (CORE-II). Since 2009, CORE-I (Normal Year Forcing) and CORE-II (Interannual Forcing) have become the standard methods to evaluate global ocean/sea-ice simulations and to examine mechanisms for forced ocean climate variability. The OMIP diagnostic protocol is relevant for any ocean model component of CMIP6, including the DECK (Diagnostic, Evaluation and Characterization of Klima experiments), historical simulations, FAFMIP (Flux Anomaly Forced MIP), C4MIP (Coupled Carbon Cycle Climate MIP), DAMIP (Detection and Attribution MIP), DCPP (Decadal Climate Prediction Project), ScenarioMIP, HighResMIP (High Resolution MIP), as well as the ocean/sea-ice OMIP simulations

Étude des relations entre la morphologie cranio-faciale et l’occlusion en denture temporaire : remodelages occipitaux et singularités basicrâniennes déterminantes pour l’occlusion

Avant toute action ou interception précoce, chez un enfant en denture temporaire, il nous paraît indispensable d’analyser de plus près certains éléments structuraux de la base crânienne de l’enfant. Pour formaliser les indications majeures d’une réelle prise en charge orthopédique, ou seulement intercepter les dysfonctions avec des appareils fonctionnels plus simples, il faut donc au préalable pouvoir classer la dysharmonie de l’enfant, squelettique et/ou dysfonctionnelle. Pour faire face à ces contraintes diagnostiques, un groupe de 243 enfants en denture temporaire a été examiné. Notre expertise clinique a permis de sélectionner des mesures céphalométriques supposées en lien avec le type de dysharmonie squelettique (à partir de repères osseux crâniens et faciaux localisés sur les téléradiographies numériques de profil). La classification occlusale a pris en compte des critères occlusaux et observé la fonction masticatoire. Les résultats statistiques (méthode experte de variables céphalométriques) montrent qu’en denture temporaire certaines architectures crâniennes privilégient un certain équilibre occlusal. Nous voyons que l’amplitude de flexion basicrânienne (ou l’angle sphénoïdal) est sous l’influence du remodelage de l’occipital : le processus de flexion ontogénique de la base et l’amplitude de fermeture de l’angle sphénoïdal dépendent essentiellement du remodelage de l’os occipital selon trois modes principaux. Des corrélations sont visibles entre ces groupes et la morphologie faciale, l’avancée ou le recul du menton. La déduction clinique importante est que la fonction masticatoire en denture temporaire s’organise selon les contraintes architecturales issues du remodelage basicrânien; l’impact des dysfonctions serait certes tributaire de la dysfonction elle-même mais aussi des singularités architecturales de la base crânienne