Search results for "Global changes"
showing 10 items of 533 documents
Changement climatique et variabilité des ressources en eau dans le bassin de l'Alibori (Bénin, Afrique de l'Ouest)
2006
International audience
Timing and patterns of ENSO impacts in Africa over the last 30 years: insights from Normalized Difference Vegetation Index data.
2012
International audience; In this study we reassess and provide a more complete picture of the timing and patterns of ENSO impacts for the whole of Africa over the three last decades. We analyse the vegetation photosynthetic activity estimated by the NOAA-AVHRR Normalized Difference Vegetation Index (NDVI) rather than rainfall itself, because NDVI allows us to document the impacts at fine space and time scales. The use of the monthly time-step adds important new insights to the findings of previous works based largely on annual or seasonal time-scales and on a regional spatial-scale: several dipolar and propagative patterns are highlighted. In addition, we show that the less-studied winter ra…
Spatial coherence of agronomic boreal monsoon onset over Western and Central Sahel (1950-2000).
2007
Poster Presentation
Etude isotopique et spatialisation du carbone dans l'agglomération dijonnaise
2005
Intraseasonal oscillations of the East African long rains and their connection with MJO activity over the Indian Ocean
2005
Our understanding of the East African long rains (March-May) variability remains relatively poor. Interannual variations are quite small compared to intraseasonal vari- ations. An analysis of pentad rainfall and OLR data shows organised variations in the range of 20-75 days, though quite irregular from year to year. However, rainfall and OLR variations are strongly consistent over the highland region only. For this region, NCEP-DOE II reanalysis data are used to detect atmospheric patterns associated to wet events. Significant zonal wind anomalies, of opposite sign at 850 and 200 hPa, are found locally over East Africa. Anomalous low-level westerlies (upper-level easter- lies) are observed d…
Concentrations de NO2 développement d'un SIG et influence de la météorologie à Dijon durant l'hiver 1999
2000
ACTI; International audience; A nitrogen dioxide (NO2) measurements campaign, with passive diffusion tubes, realised by ATMOSF'Air during the winter 1999, allows to realise an atmospheric pollution study in the Dijon urban area. In order to understand the spatial NO2 distribution in the urban area, NO2 is correlated with NO emissions and topography thanks to a Geographical Information System (GIS). With a multiple linear regression, NO2 concentrations are explained principally by traffic and topography. A Principal Components Analysis shows the necessity to nuance the relation between these variables. So, the meteorological datas of Dijon-Longvic, could explain the different NO2 distributio…
The Madden-Julian Oscillation (MJO) impacts on Southern African summer rainfall and Tropical-Temperate Interactions
2006
Composite maps of outgoing longwave radiation (OLR) anomalies over the Madden–Julian oscillation (MJO) cycle show marked intraseasonal fluctuations over southern Africa (south of 15°S). Large-scale convective clusters are seen to propagate eastward and then northward over the continent, mainly between 10° and 20°S. The corresponding response of the rainfall field presents the alternation, over the cycle, of dry and humid phases, which are both significant. Moisture flux anomalies indicate an intraseasonal modulation of the midtropospheric easterly flow over the Congo basin at 700 hPa; these fluctuations are coupled to meridional flux anomalies that extend from the tropical to the subtropica…
La mousson africaine dans un modèle de circulation générale quasi-parfait
2010
Le modèle de circulation générale ARPEGE-Climat du CNRM présente des biais secs relativement marqués en Afrique de l'Ouest pendant la mousson, même lorsqu'il est forcé par des termpératures de surface marine observées. Les précipitations sahéliennes restent très inférieures aux observations, en lien avec un flux de mousson de basse troposphère trop faible sur la bande guinéenne et l'océan Atlantique équatorial. On propose ici de guider le modèle ARPEGE-Climat vers les réanalyses ERA-40 en dehors d'une fenêtre comprenant l'Afrique de l'Ouest et le proche Atlantique (technique dite de nudging en point de grille). Ce protocole nous permet de: (i) analyser l'origine régionale ou de large échell…
Downscaling West African climate : uncertainties, sensitivity to the model physics and regional variability
2013
We present here a set of regional climate simulations, complementary to the CORDEX-Africa modeling exercice, performed over West Africa during the 1989-2010 period using the non-hydrostatic model WRF. Lateral and SST forcings are provided by ERA-Interim reanalyses. The regional domain [45W 45E 10S 30N] encompasses West Africa and the nearby Atlantic Ocean and Gulf of Guinea. The grid resolution is moderate (80km, with 28 levels on the vertical) in order to reduce computational costs and multiply sensitivity experiments. A first set of fifteen 20-year long simulations addresses the influence of the model physics (convective, radiative and land surface schemes). A second set of simulations co…
Montagnes d'Afrique Tropicale : marqueurs de la variabilité climatique ou isolats climatiques ?
2011
International audience; Tropical mountains are often seen as beacons of past and present-day climate change. However, do they actually reflect interannual and decadal-scale climatic variability of the surrounding areas ? At the scale of Africa South of the Sahara, an analysis of the 1941-2000 rainfall variability shows that spatial coherence is seldom modified by relief. Examples are presented in which mountain climates are even indicators of large-scale atmospheric dynamics and climate variability.