Search results for "Clima"
showing 10 items of 6069 documents
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.
Typology of intraseasonal oscillations based on a Local Mode Analysis
2007
The Intraseasonal Oscillation (ISO; 20-120 day) is an important component of the variability of the Tropical convection that strongly perturbs the Asian and the Aus- tralian monsoons. Our knowledge of the physical origin of the ISO however remains largely incomplete, partially because of the large variability of its characteristics from one event to another. The aim is to determine how the patterns of the different ISO events may be objectively regrouped in a few types, related for example to season, ENSO or other large scale forcing. Patterns of the different ISO events are extracted using a Local Mode Analysis (LMA, Goulet and Duvel 2000). The LMA is based on complex empirical orthogonal …
Pourquoi mettre la pression sur le dioxyde de carbone ?
2009
7 pages
Influence de l'Oscillation de Madden-Julian sur la variabilité intrasaisonnière des pluies en Afrique de l'Est (Kenya-Tanzanie)
2005
Les incidences de l'Oscillation de Madden-Julian, mode de variabilité atmosphérique intrasaisonnier dominant dans la bande tropicale, sur la répartition des pluies d'Afrique de l'Est durant le trimestre Mars-Avril-Mai, sont étudiées sur la période 1979-2002. L'analyse révèle une modulation significative des précipitations. Cependant, de fortes hétérogénéités existent du point de vue des pluies entre les Hautes terres et la côte kenyane, couplées à des mécanismes pluviogènes de nature différente.