Active phases and pauses of the West African monsoon and associated atmospheric dynamics

International audience

Detection of intraseasonal leading signals for the rainfall onset over the Sudanian and Sahelian belts

International audience

Statistical analyses of the impact of climatic parameters on the vectors of Malaria over West-Africa

Changes in the frequency of the Weather Regimes over the Euro-Atlantic and Mediterranean sector and their relation to the anomalous temperatures over the Mediterranean Sea.

19 pages; International audience; An exercise has been carried out to assess to what extent the Euro-Atlantic Weather Regimes (WR),described from the ERA-interim Reanalysis in the summer season, projects onto a pool of AGCMAMIPsimulations in which sea surface temperatures (SST) are prescribed from observations.Although the model simulations present some biases in the spatial structure and seasonality of WRs,exhibiting also less variability, they are able to capture main WR over the region in summer season:+Middle East –Middle East, +NAO, -NAO. WR paradigm is used to quantify changes in theatmosphere under warmer/colder than normal conditions over the Mediterranean Sea. To addressthis proble…

Interaction between the West African Monsoon and the summer Mediterranean climate: An overview.

15 pages; International audience; Although in the framework of the global climate research the Mediterranean climate variability andthe West African Monsoon (WAM) dynamics have been considered for a long time as “passive”systems, i.e., prone to the influence of large scale ocean and atmospheric variability, over the lastdecade many studies have been dedicated to the WAM-Mediterranean interaction and the active roleof these climate systems has been highlighted. This article presents the WAM-Mediterraneanteleconnection through an overview of the recent literature, describing the observational evidencesand the dynamical mechanisms underlying this climate teleconnection. The influence of the Me…

Modulations intra-saisonnières de la pluviométrie ouest africaine: pauses et phases actives du système de mousson

National audience; En Afrique de l'Ouest, le déclenchement des différentes saisons des pluies ainsi que les rythmes pluviométriques sont principalement liés à la phase d'installation du système de mousson. Cette étude montre que cette phase peut se décomposer en quatre sous-périodes distinctes, assez fixes dans le temps, appelées « pauses » pendant lesquelles les pluies stagnent, voire décroissent. Ces pauses sont suivies par de fortes croissances des précipitations appelées « phases actives ». Dans le cadre d'études épidémiologiques portant sur des maladies à vecteur très dépendant des précipitations, type paludisme, ces résultats offrent des perspectives de recherches intéressantes.

Definition and predictability of the beginning of the rainy season over North Vietnam

Regional scale model simulation for West Africa using a Mesoscale Model MM5

Dynamical downscaling is considered as a good tool for deriving regional climate in formation based on large scale climate conditions because they can represent surface conditions like topography and vegetation more realistic than GCM. The fifth generation Pennsylvania State University (PSU)-National Centre for Atmospheric Research (NCAR) Mesoscale Model MM5 is used to study the regional scale process that control West African rainfall, its associated circulations and other surface features. The simulations are carried out for seven months from March to September using 1.125X1.125 degree lat/lon version of ECMWF reanalysis data for defining the initial and laternal boundary conditions. The …

Onset of the Summer Monsoon over the Southern Vietnam and its Predactibility

soumis; International audience

Active phase and pauses of the West African monsoon and associated atmospheric dynamics

This study comes within the research of the characterization of the intra-seasonal modulations of the West Africa monsoon system during its annual cycle. Indeed, these fluctuations are not yet well understood and documented, particularly with regard to the main periods of installation of the various Western African rainy seasons and the phases of transition separating them. Also very few studies were interested in these onsets. Objective diagnostic analyses based on PCA decomposition, Varimax rotation and low-pass filters (≥ 1 month) are performed on the 5-day CMAP rainfall data over West Africa. The northward excursion of the rainbelt can be divided into 4 basic sub-periods each composed o…

Climate adjustments over the African-Indian monsoon regions accompanying Mediterranean Sea thermal variability

International audience; This study analyses the atmospheric and rainfall anomaly patterns in the African/Indian monsoon region concomitant of warm/cold anomalies confined in the Mediterranean sea in northern summer. It examines first the similarities and contrasts observed in longitudes, then discusses the results obtained regarding the normal in terms of climate impacts in the Sahelian belt. Statistical results show an opposite African/Indian relationship with stronger (weaker) African (Indian) tropical circulations occurring in warmer (colder) Mediterranean situations and favouring significant increases (decreases) in monsoon circulation, atmospheric moisture content and deep convection, …

Which rainfall dataset can be used to study African Monsoon?

Multi-scale study of the rainy season onset over the Sudano-Sahelian belt: Spatial coherence and potential predictability

The spatial coherence of boreal monsoon onset (July-September) over the western and central Sahel is studied through the analysis of daily rainfall records for 136 rain-gauges from 1950-2000. Onset of the rainy season has been defined using 3 definitions which rely on 3 overlapped spatial scales: (i) the regional scale, i.e. the northward ITCZ jump from Guinean to Soudano-Sahelian latitudes, (ii) the meso-scale related with the first occurrence of the main rainfall-generating phenomenon, that is squall line and (iii) the local-scale of the first rainfall recorded at the rain-gauge. Local and meso-scale onsets show a weak degree of instantaneous and inter-annual spatial coherence, meaning th…

Méditerranée et mousson africaine : mécanismes et évolution dans l’actuel et le futur.

6 pages; International audience; À partir d’observations in situ et analysées, de réanalyses atmosphériques, d’expériences numériques forcées parles températures de la Méditerranée, et de sorties CMIP5 issues de seize modèles couplés ayant participé au dernier exercicedu GIEC, nous tentons une synthèse des travaux collaboratifs entrepris au CRC ces cinq dernières années et portant sur lesinteractions tropiques/extra-tropiques au long du fuseau africain et sur leurs liens avec la mousson africaine. Après avoirrappelé le rôle des téléconnexions avec les grands bassins océaniques, de la circulation sur le secteur euro-atlantique et dela mousson indienne via le mécanisme de Rodwell-Hoskins, nou…

Predictability of July-August rainfall over Western and Central Sahel using the 63 DEMETER coupled simulations

Definition and predictability of an ORL monsoon onset in the West Africa monsoons

International audience

On the link between aerosols and meningitis in Western Africa

Variabilité intrasaisonnière des précipitations et de leur distribution : impacts sur le développement du couvert végétal dans le Nord du Cameroun (1982-2002)

variabilité, séquences sèches, précipitations, intrasaisonnier, végétation, Nord-Cameroun; International audience; La variabilité intrasaisonnière des précipitations est étudiée dans le Nord-Cameroun (6°N-13°N et 11°E-16°E), à partir des données journalières d'une vingtaine de stations, ainsi que leur relation avec la variabilité du couvert végétal, à travers les données bimensuelles de NDVI (Normalized Difference Vegetation Index) à 8Km de résolution, le tout sur la période 1982-2002. En domaine soudanien (situé au sud du 9°N), la saison des pluies (Pmensuel>50mm) s'étend entre les mois d'avril à octobre, et entre Mai à septembre en domaine sahélien (nord du 9°N). Dans l'ensemble, les anom…

Les aérosols désertiques, un facteur potentiel des épidémies de méningite en Afrique de l'Ouest

International audience