Search results for "Universe"
showing 10 items of 2171 documents
How do tropical temperate troughs form and develop over southern Africa?
2014
16 pages ; Corrigendum Figure (Macron C, B Pohl, Y Richard & M Bessafi (2014) CORRIGENDUM. Journal of Climate, 27, 5198-5199. doi:10.1175/JCLI-D-14-00319.1); International audience; This paper aims at separating the respective influences of tropical and midlatitude variability on the development and life cycle of tropical temperate troughs (TTTs) over southern Africa in austral summer (November-February). Cluster analysis is applied to 1971-2000 40-yr ECMWF Re-Analysis (ERA-40) daily outgoing longwave radiation (OLR) anomalies to identify TTTs and monitor tropical convection. The same analysis applied to the zonal wind stretching deformation at 200 hPa (ZDEF) characterizes midlatitude trans…
Multiscale study of rainfall and vegetation cover in Cameroon : spatial analysis, temporal trends, climatic and anthropogenic factors of NDVI variabi…
2011
Due to its shape and location (2°N-13°N – 8°E-16°E; proximity of the Atlantic Ocean), Cameroon is characterized by a panel of cross-regional climate encountered widely in tropical Africa. Over the region, the decrease rainfall during the second half of the last century has been shown to be associated with stronger recurrence of drier periods, specifically in the core of the rainy season. These conditions have favored the degradation of vegetation cover, driven by socioeconomic and demographic constraints. The substantial impacts on human activities and local society highlight the need to better understand how climate and environmental dynamics do interact locally. The aim of this study is t…
Timing and patterns of the ENSO signal in Africa over the last 30 years: insights from normalized difference vegetation index data.
2014
Abstract A more complete picture of the timing and patterns of the ENSO signal during the seasonal cycle for the whole of Africa over the three last decades is provided using the normalized difference vegetation index (NDVI). Indeed, NDVI has a higher spatial resolution and is more frequently updated than in situ climate databases, and highlights the impact of ENSO on vegetation dynamics as a combined result of ENSO on rainfall, solar radiation, and temperature. The month-by-month NDVI–Niño-3.4 correlation patterns evolve as follows. From July to September, negative correlations are observed over the Sahel, the Gulf of Guinea coast, and regions from the northern Democratic Republic of Congo…
Water status modelling : impact of local rainfall variability in Burgundy (France)
2016
6 pages; International audience; Water status is a key factor in vine development and berry ripening. Water status is strongly affected byenvironmental parameters such as soil and climate. Whereas at local scale the soil variability is frequentlyaccounted for, little scientific reports are available concerning the impact of local rainfall variability ongrapevine water status. In order to accurately register the space and time variations of rainfall at local scale, adense rain-gauges network has been installed in Burgundy. It is composed of 45 rain-gauges over a 28 km² area.Rainfall data collected by each rain-gauge in 2014 and 2015 was used as input variables in the grapevine waterbalance m…
Early Cambrian origin of modern food webs: evidence from predator arrow worms.
2007
7 pages; International audience; Although palaeontological evidence from exceptional biota demonstrates the existence of diverse marine communities in the Early Cambrian (approx. 540-520 Myr ago), little is known concerning the functioning of the marine ecosystem, especially its trophic structure and the full range of ecological niches colonized by the fauna. The presence of a diverse zooplankton in Early Cambrian oceans is still an open issue. Here we provide compelling evidence that chaetognaths, an important element of modern zooplankton, were present in the Early Cambrian Chengjiang biota with morphologies almost identical to Recent forms. New information obtained from the lowermost Cam…
Zirconium–hafnium and rare earth element signatures discriminating the effect of atmospheric fallout from hydrothermal input in volcanic lake water
2016
The geochemical behaviour of Rare Earth Elements, Zr and Hf was investigated in the thermal waters of Nevado del Ruiz volcano system. A wide range of pH, between 1.0 and 8.8, characterizes these fluids. The acidicwaters are sulphate dominatedwith different Cl/SO4 ratios. The important role of the pH and the ionic complexes for the distribution of REE, Zr a nd Hf in the aqueous phase was evidenced. The pH rules the precipitation of authigenic Fe and Al oxyhydroxides producing changes in REE, Zr, Hf amounts and strong anomalies of Cerium. The precipitation of alunite and jarosite removes LREE from the solution, changing the REE distribution in acidic waters. Y-Ho and Zr-Hf (twin pairs) have a…
Structures de déformation induites par surpressions de fluide dans les environnements sous-glaciaires et marin profonds : implications paléoenvironne…
2014
Soft-sediment deformation structures (SSDs) occur in unconsolidated sediments, during or shortly after deposition. SSDs are abundant in subglacial and deep-marine environments because of the development of fluid overpressure. Case studies of these two sedimentary environments were used (1) to reconstruct palaeoenvironments from SSDS, and (2) to define the impacts of SSDS on glacial morphologies and (3) petrophysical properties.(1) Analyses of strain regimes, deformation mechanisms, and chronologies in SSDs served to improve palaeoenvironmental reconstructions. These structures were used as proxys to estimate variations of ice flow velocities, ice thickness, meltwater production, and positio…
Stratigraphic modelling of platform architecture and carbonate production: a Messinian case study (Sorbas Basin, SE Spain).
2016
27 pages; International audience; The late Messinian mixed carbonate-siliciclastic platforms of the Sorbas Basin, known as the Terminal Carbonate Complex, record significant changes in carbonate production and geometry. Their facies and stratigraphic architecture result from complex interactions between base-level fluctuations, evaporite deformation/dissolution and detrital inputs. A 3D quantitative approach (with DIONISOS software) is used to explore the basin-scale platform architecture and to quantify the carbonate production of the Terminal Carbonate Complex. The modelling strategy consists in integrating detailed 2D field-based transects and modern carbonate system parameters (e.g. car…
Improvement of snow physical parameters retrieval using SAR data in the Arctic (Svalbard)
2018
International audience; Arctic snow cover dynamics offer a changing face in terms of temporal duration andwater equivalent, due to recent climate change conditions (Callaghan et al., 2011; Lemke & Jacobi,2012). Indeed, the Arctic is now experiencing some of the most rapid and severe climate change onearth. In this context, innovative and improved methods are helpful to enhance management of thesnow-pack resource for climate research, hydrology and human activities. The characteristics of Arcticsnow are different from “temperate” snow (i.e. the Alps), in terms of thickness, internal structure, thermalconductivity, and metamorphism. Ground observation often indicates wind slab at the snow sur…
Karstologie et remplissage sédimentaire du gisement pléistocène de Romain-la-Roche (Doubs, France).
2010
19 pages; International audience; Le gisement pléistocène du site de Romain-la-Roche (commune de Romain dans le Doubs) correspond au remplissage épikarstique d'un aven affectant les calcaires du Jurassique moyen d'un plateau situé au nord du massif jurassien. Cette cavité, située en dehors de l'extension de la calotte du dernier maximum glaciaire, a été façonnée par un flux hydrologique en liaison avec un drainage de surface qui a vraisemblablement disparu au cours du Pliocène lors d'une phase d'inversion du relief de part et d'autre de la faille normale qui délimite la partie ouest du plateau. Avant son colmatage au cours du Pléistocène la cavité était reliée à un réseau dense de conduits …