Search

Cet ouvrage livre les premiers résultats des recherches sur les occupations amérindiennes du bassin du Sinnamary (1660-220 BP), menées à l’occasion de la construction par Électricité de France du barrage de Petit Saut (Guyane française). À une approche méthodologique sur le milieu tropical sylvestre et fluvial, succèdent l’étude des sites de plein air et un point sur le phénomène de terra preta et des paléoincendies. Pour la première fois sont proposés un cadre typologique et un vocabulaire appliqués aux séries lithiques et aux sites à polisson, ainsi qu’une analyse de la céramique selon deux approches complémentaires : détermination des lieux de fabrication à partir de la composition chimique des pâtes, codification des formes et des décors des quelque 22 000 artefacts enregistrés. Après la publication consacrée à la période coloniale de cette région (dAf 60), ce volume constitue une solide contribution au renouvellement de l’historiographie du plateau des Guyanes. This work introduces the initial results of research at sites occupied by Native Americans in the Sinnamary basin (1660-220 BP), carried ont at the time of the construction of the Petit Saut dam by Electricité de France in French Guyana. A methodological approach pertaining to the tropical sylvan and riparian milieu is followed by a study of the open-air sites, and a commentary focusing on the phenomenon of terra preta and palaeolithic fires. For the first time a typological tramework and a vocabulary are proposed for reference to lithic senes and polishing-tool sites. This work also includes a study of ceramics using two complementary approaches: determination of place of manufacture based on the Chemical make-up of the pestes employed, and codification of the forms and motifs of the 22,000 objects registered. Following up on the publication devoted to the colonial period in this region (dAf 60), this volume makes a signifiant contribution to the renewal of histonographical work on the Guyana plateau.

International audience

International audience; The ability to perform multiple-Doppler wind synthesis from operational weather radar systems on an operational basis has been investigated by the French Weather Service since 2006 using a (sub-)network of six Doppler radars covering the Greater Paris area. This analysis has been recently extended to the entire French radar network so as to implement a nationwide, three-dimensional reflectivity and wind field mosaic to be eventually delivered to forecasters and modellers, as well as automatic nowcasting systems for air traffic management purposes. In this composite analysis, data collected by all 24 radars of the French radar network are collected, pre-processed and combined in real time at intervals of 15 minutes to retrieve the complete wind vector (u,v,w) and reflectivity fields at a horizontal resolution of 2.5 km within a domain of approximately 1000 × 1000 × 12 km3. In order to illustrate the performance of this new product, examples of 3-D wind and reflectivity output produced during the passage of two significant weather events are presented: the extratropical storm Klaus, which struck France on 24 January 2009 with hurricane-force gusts, and a typical orographic high-impact precipitation event that developed on 21 October 2009. The evaluation of real-time radar outputs against operational analyses attests to the consistency of the retrieved wind fields.

National audience; The 1000 municipalities in the region Provence-Alpes-Cote d'Azur are exposed to at least one of the five following hazards: flash floods, mudslides, landslides, avalanches and forest fires. In the three departments of this mountain region (Alpes de Haute Provence, Hautes Alpes and Alpes Maritimes), a hundred of them is exposed to five. The occurrence and intensity of these fluctuations depend more or less directly on the quantity and nature of precipitation. However, in the French Alps, the visibility of the radar national network ARAMIS is considerably reduced by the masking effects of terrain, clutter and altitude of the beam. Accordingly, there is a poor quality for the estimated rainfall. In this context, the project RHYTMME jointly run by Météo-France and Cemagref, provides: - To supplement the existing radar network by new technology radar deployment (radar Doppler polarimetric X-band) in the Southern Alps; - To develop downstream of this network, a service platform to manage natural hydrometeorological risks, especially in the mountains. This article presents the strategy adopted to improve radar coverage in the Southern Alps and relates an example obtained by a first X-band radar information (radar Hydrix) already in service in the Maritime Alps.; Les quelques 1000 communes de la région Provence-Alpes-Côte d'Azur sont exposées à au moins l'un des cinq aléas suivants : crues éclairs, laves torrentielles, mouvements de terrain, avalanches et feux de forêts. Dans les trois départements de montagne de cette région (Alpes de Haute Provence, Hautes Alpes et Alpes Maritimes), une centaine d'entre elles est exposée aux cinq. L'occurrence et l'intensité de ces aléas dépendent plus ou moins directement de la quantité et de la nature des précipitations. Or, sur l'arc alpin français, la visibilité des radars du réseau national ARAMIS est considérablement réduite par les effets de masque du relief, d'échos fixes et d'altitude du faisceau. En conséquence, l'estimation des cumuls de pluie y est de qualité médiocre. Dans ce contexte, le projet RHYTMME, piloté conjointement par Météo-France et le Cemagref, prévoit : - de compléter le réseau de radars existant par le déploiement dans les Alpes du Sud de radars de nouvelle technologie (radars Doppler polarimétriques en bande X) ; - de développer, en aval de ce réseau, une plateforme de services d'aide à la gestion des risques naturels hydrométéorologiques, notamment en montagne. Cet article présente la stratégie adoptée pour améliorer la couverture radar dans les Alpes du sud et rapporte un exemple d'observation de phénomène torrentiel permise par un premier radar en bande X (radar Hydrix) déjà en service dans les Alpes Maritimes.

This paper describes the development of the thunderstorm weather information management system “CB WIMS” within the European Integrated Project FLYSAFE and presents results from applications in case studies over the terminal manoeuvring area of airport Paris Charles de Gaulle.

The main objective of this paper is to evaluate, for urban scales, the quality of the new French operational radar processing chain developed by Meteo France. This product is deployed within the French operational radar network. The evaluation is done by comparing radar data (1 km² resolution) to rain gauge data at four different time scales i.e. 5, 15, 30 and 60 min. Radar data is given by the radar of Trappes located 30 km south-west of Paris. 87 rain gauges located from 0 to 135 km around the weather radar provide the ground reference data. The data set consists in 50 varied rainy days. The influence of the distance, of the quality of the radar data and of the rain type as well as of the adjustment factor is analysed. The present analysis finally tries to evaluate the error peculiar to the reference data by considering instrumental and representativeness errors in order to take into account the accuracy of the reference data in the radar/rain gauge comparison.

International audience; The potential value of operational Doppler radar networks for high resolution wind forecast verification is investigated through comparing wind outputs of the cloud resolving model AROME against newly available operational multiple-Doppler winds in northern France. Quantitative comparisons of radar and model winds for a 16-h frontal precipitation event show good agreement, with differences in wind speed (resp. direction) generally comprised between ±2.5 m.s−1 (resp. ±15°). Power spectra deduced from the scale decomposition of radar and model outputs also show good agreement through all scales. The method is also applied to validate the divergence structures as analyzed by AROME's 3Dvar assimilation system that considers, among a comprehensive set of observation types, the same radial velocities than those considered in the wind retrieval.

During Intensive Observing Periods (IOP) of the Mesoscale Alpine Programme (MAP, see Bougeault et al. 2001) a network of three Doppler radars was operated in the Lago Maggiore Target Area (LMTA). In the afternoon and evening of Sept. 17, 1999 (MAP-IOP2a), a major squall line formed on the foothills of the southeastward facing slopes of the Lago Maggiore region and intensified during its propagation to the east as a three-dimensional con­vective cluster. This intense orogenic system with lots of lightning impacts and precipitation amounts of more than 70 mm in 6 hours, was well observed by the radars. Additional polarimetric data from radar S-POL (NCAR) revealed rich regions of grau­pel/hail mixture in convective cells where the verti­cal velocity, w 2: 4 ms-1 and the radar reflectivity, Z 2: 45 dBZ (Tabary et al., 2001).