Characterization of air-sea exchanges over the Western Mediterranean Sea during HyMeX SOP1 using the AROME-WMED model

International audienceAir-sea exchanges play an important role during intense weather events over the Mediterranean Sea, especially in supplying heat and moisture for heavy precipitation events, which often affect the area. Observations collected during the first Hydrological cycle in the Mediterranean Experiment (HyMeX) Special Observation Period (SOP1) over the Western Mediterranean area in autumn 2012 provide an unprecedented dataset for assessing the capabilities of numerical weather prediction systems to represent the air-sea interface and marine boundary layer during the heavy precipitation season. A HyMeX-dedicated version of Application de la Recherche a l'Operationnel a Meso-Echelle, in French (AROME) covering the whole western Mediterranean basin, named AROME-WMED, was evaluated through comparisons against moored buoys, drifting buoys and ship measurements deployed during the HyMeX campaign. A general, good agreement is found for near-surface meteorological parameters, whereas significant discrepancies are observed during strong air-sea exchange periods. The two main reasons are that (1) sea-surface temperature (SST) is kept constant during the model runs and (2) sensible heat flux is overestimated in strong wind regimes by the AROME turbulent flux parametrization. Air-sea exchanges during SOP1 were characterized thanks to AROME-WMED short-range (1-24h) forecasts. This shows some areas of strong air-sea fluxes in the Gulf of Lion and the Balearic, Ligurian and Tyrrhenian Seas. The Gulf of Lion is the area showing the highest variability of air-sea fluxes, due to dominant strong regional winds (Mistral/Tramontane). Whereas some heavy precipitation events occur without significant air-sea fluxes, all strong air-sea exchange events include, or occur only 1 or 2 days before, heavy precipitation events. A detailed analysis of an Intense Observation Period (IOP) dedicated to a heavy precipitation event (IOP13, from 12-15 October) illustrates how both dynamic (wind) and thermodynamic (temperature and humidity gradient effect) contributions influence air-sea flux evolution

Contraintes et potentialités du droit public dans la gestion négociée du risque d'inondation

Reflet de l'évolution d'une société, de ses rationalités et de ses irrationalités, de ses doutes et de ses certitudes, le droit constitue un point d'observation privilégié de son fonctionnement.La recherche engagée a été menée dans la perspective d'une dialectique entre la capacité du droit à impulser une évolution sociale, et son aptitude à opposer des freins à cette évolution. Elle porte sur l'analyse du processus décisionnel et du cadre juridique mis en oeuvre pour une gestion territoriale du risque d'inondation. A travers l'établissement d'un diagnostic critique du cadre juridique actuel, de sa pertinence et de ses limites, la recherche est ciblée sur l'étude de faisabilité de solutions négociées dans une gestion territoriale du risque d'inondation.Des évolutions sociétales majeures constituent le cadre d'un renouveau de la politique de gestion des risques, qui voit émerger une conception territoriale de la gestion du risque d'inondation accompagnée d'une évolution importante des politiques de prévention des risques, éléments dont nous allons nous attacher à décrire les caractères essentiels dans le chapitre 1. Par l'analyse de cinq cas de terrain, l'étude illustrera par son chapitre 2 comment, dans ce contexte, le pragmatisme local prévaut en matière de gestion territoriale du risque d'inondation. Ces évolutions socio-politiques s'inscrivent dans le contexte du droit public dont l'évolution peut s'interpréter entre statu quo et ouverture sur les démarches participatives. Le chapitre 3 s'attachera à analyser de manière rigoureuse, d'une part, le cadre juridique de la concertation, d'autre part, les ouvertures et les limites de la contractualisation, considérée comme l'aboutissement formel de la négociation.C'est à la lumière de ces multiples évolutions que nous pourrons comprendre au chapitre 4 les contraintes et potentialités du droit public pour la gestion territoriale du risque d'inondation. Enfin, le chapitre 5 ouvrira des pistes de réflexion complémentaires sur un volet apparu comme particulièrement important dans la mise en oeuvre de projets de gestion territoriale, celui de la maîtrise foncière

Out of Africa: detrital zircon provenance of central Madagascar and Neoproterozoic terrane transfer across the Mozambique ocean

The Neoproterozoic East African Orogen reflects closure of the Mozambique Ocean and collision of the Congo and Dharwar cratons. This palaeogeographic change and its environmental consequences are poorly understood, but new detrital zircon ages from Madagascar and published data from elsewhere provide evidence for multiple ocean basins and two-stage collision. We propose that central Madagascar rifted from the Congo Craton and crossed a Palaeomozambique Ocean to collide with the Dharwar Craton at c. 700 Ma, opening a Neomozambique Ocean in its wake. Closure of the Neomozambique Ocean at c. 600 Ma juxtaposed the Congo and Dharwar cratons and resulted in prolonged collisional orogenesis concluding at c. 500 Ma

High-resolution air-sea coupling impact on two heavy precipitation events in the Western Mediterranean

International audienceThe Mediterranean Sea is an important source of heat and moisture for heavy precipitation events (HPEs). Moreover, the ocean mixed layer (OML) evolves rapidly under such intense events. Whereas short‐term numerical weather prediction systems generally use low‐resolution non‐evolving sea surface temperature (SST), the development of high‐resolution high‐frequency coupled system allows us to fully take into account the fine‐scale interactions between the low‐level atmosphere and the OML which occur during HPEs.The aim of this study is to investigate the impact of fine‐scale air–sea interactions and coupled processes involved during the HPEs which occurred during 12–15 October 2012 (IOP13) and 26–28 October 2012 (IOP16a/b) of the HyMeX first field campaign. For that purpose, the high‐resolution coupled system AROME‐NEMO WMED was developed. This system is based on the 2.5 km‐resolution non‐hydrostatic convection‐permitting atmospheric model AROME‐WMED and the 1/36°‐resolution NEMO‐WMED36 ocean model. The coupling frequency is 1 h. To distinguish the effects due to the change in the initial SST field from that due to the interactive 3D ocean, the coupled run is compared to two AROME‐WMED atmosphere‐only experiments with no SST evolution during the 48 h forecast cycles—one using the AROME‐WMED SST analysis, the second using the SST field of the coupled experiment each day at 0000 UTC. The results of the three experiments re‐assert that the SST initial condition strongly influences the HPE forecast, in terms of intensity and location. With water budget analyses, the significant impact of the ocean interactive evolution on the surface evaporation water supply for HPEs is also highlighted. In cases of strong and intense air–sea exchanges, as in the mistral event of IOP16b, the coupling reproduces the intense and rapid surface cooling and demonstrates the importance of representing the ocean turbulent mixing with entrainment at the OML base

SURFEX v8.0 interface with OASIS3-MCT to couple atmosphere with hydrology, ocean, waves and sea-ice models, from coastal to global scales

This study presents the principles of the new coupling interface based on the SURFEX multi-surface model and the OASIS3-MCT coupler. As SURFEX can be plugged into several atmospheric models, it can be used in a wide range of applications, from global and regional coupled climate systems to high-resolution numerical weather prediction systems or very fine-scale models dedicated to process studies. The objective of this development is to build and share a common structure for the atmosphere–surface coupling of all these applications, involving on the one hand atmospheric models and on the other hand ocean, ice, hydrology, and wave models. The numerical and physical principles of SURFEX interface between the different component models are described, and the different coupled systems in which the SURFEX OASIS3-MCT-based coupling interface is already implemented are presented

Facies analyses, chronostratigraphy and paleoenvironemental reconstructions of jurassic to cetaceous sequence of the Congo basin

International audienceThe Congo Basin is characterized by an extensive and relatively thick (ca. 1 km) succession of Jurassic-Cretaceous sedimentary sequences that preserves a unique record of the tectonic and climatic evolution of central Africa during the main period of break-up of Gondwana and the emergence of the Indian and South Atlantic Oceans. New facies analysis and detailed correlations of these ‘Congo’ sequences are described from field observations in the southwestern Congo Basin and by re-logging cores and well logs from four deep boreholes drilled in the center of the basin in the 1950s and 1970s. The lowermost Upper Jurassic sequence (the Stanleyville Group) records a short marine incursion of the proto-Indian Ocean into the northern Congo Basin, and is in turn overlain to the south by widespread aeolian dune deposits (the Lower Kwango Group), which correlate well with other Upper Jurassic to Lower Cretaceous aeolian sequences in Namibia and eastern Brazil, attesting to a giant ‘Sahara-like’ paleo-desert across central West Gondwana, just before the separation of Africa from South America. U-Pb detrital zircons geochronology from this aeolian sequence in the Congo Basin dates mid-Silurian (ca. 430 Ma), Permian-Triassic (ca. 240 and 290 Ma) and Jurassic (ca. 190 Ma) magmatic zircons, here proposed to have been sourced from abundant volcanic activity along the proto-Andes, in southernmost Gondwana. Two successive middle Cretaceous lacustrine sequences in the center of the Congo Basin (the Loia and Bokungu Groups), first analcime-rich and episodically anoxic, and then more carbonated, are interpreted to record an episode of basin stagnation following the eruption of the Paraná-Etendeka Large Igneous Province and a subsequent hot/humid climate maximum during the opening of the South Atlantic Ocean. Late Cretaceous sedimentation in the Congo Basin terminated with fluvial sediments (the Upper Kwango Group) suggesting marginal uplifts during the Kalahari epeirogeny. The top of these sequences is truncated by a regional Cenozoic peneplanation surface