Mesure de la réfractivité atmosphérique par radar météorologique : comparaison avec un réseau de capteurs au sol.

International audienceLes radars météorologiques peuvent mesurer les changements de l'indice de réfraction de l'air dans les basses couches de l'atmosphère (Fabry et al., 1997, Fabry 2004). En utilisant les changements de phase provenant de cibles fixes aux alentours du radar, cette mesure permet d'obtenir une mesure de la réfractivité atmosphérique. Celle-ci dépend de la pression, la température et l'humidité. Les échos exploitables proviennent en général des cibles fixes telles que des châteaux d'eau, des tours ou des pylônes électriques. Pendant la campagne HyMeX (Hydrological cycle in Mediterranean expriment), cette mesure a été implémentée avec succès sur les radars bande S du réseau opérationnel de Météo-France. Afin de mieux comprendre les sources d'erreur autour de cette mesure, en particulier lorsque l'on monte en fréquence, Besson et al. 2012 a mené une simulation à partir des données de stations météorologiques automatiques. Cela a permis de mettre en avant une plus forte variabilité du signal l'été et en fin d'après-midi, quand la réfractivité est très sensible aux changements d'humidité. Cette simulation a ensuite été confirmée par des mesures radar. Est-il alors possible d'obtenir une information sur la turbulence à partir de cette mesure ? Pour échantillonner la variabilité spatiale et temporelle de la réfractivité, une analyse a été menée sur un an de données provenant du radar en bande C de Trappes, conjointement à une comparaison avec les stations automatiques alentours. L'étude présentée ici a permis de montrer qu'un lien qualitatif et quantitatif peut être établi entre les variabilités de la réfractivité mesurée par radar ou par les stations automatiques, qui sont liées à la turbulence atmosphérique de basses couches

BASTA : a 95GHz FM-­‐CW Cloud radar

International audienceGround-based continuous observation of non-precipitating clouds and fo

Use of multi-sources 10-years quantitative precipitation estimation re-analyses in a lumped rainfall-runoff model

International audienceL'objectif principal de ce projet est de produire une base de donnée de référence couvrant une période de 10 ans pour l'estimation quantitative de lames d'eaux précipitées (LEP). L'objectif est d'utiliser de façon optimale l'ensemble des informations disponibles (radars, pluviomètres horaires et journaliers, données atellite....) afin d'obtenir la meilleure estimation possible de la pluie précipitée. La base de données résultante sera une série de LPE horaire, de 1km2, associée a une estimation des incertitudes sur l'ensemble du territoire français. Cela sera une référence commune pour les hydrologues, permettant des applications telles que le calage des paramètres de modèles, l'evaluation de la valeur ajoutée d'une entrée spatio-temporelle haute résolution pour les modèles hydrologiques ect... / This project main objective is to produce a 10-year reference database of Quantitative Precipitation Estimations (QPE). The objective is to make use optimally at any time of all the available information (radars, hourly and daily rain gauges, satellite data, etc) to obtain the best possible surface precipitation estimation. The resulting data base, will consist of hourly, 1km² gridded QPE and associated estimation uncertainties over the entire French territory. This will represent a common reference for hydrologists useful for various applications such as the calibration of the hydrological model parameters, the assessment of the the added value of high space-time resolution input for hydrological models, etc

Effectiveness of Meningococcal B Vaccine against Endemic Hypervirulent Neisseria meningitidis W Strain, England

Serum samples from children immunized with a meningococcal serogroup B vaccine demonstrated potent serum bactericidal antibody activity against the hypervirulent Neisseria meningitidis serogroup W strain circulating in England. The recent introduction of this vaccine into the United Kingdom national immunization program should also help protect infants against this endemic strain

The catastrophic flash-flood event of 8–9 September 2002 in the Gard region, France: a first case study for the Cévennes–Vivarais Mediterranean Hydrometeorological Observatory

The Cévennes–Vivarais Mediterranean Hydrometeorological Observatory (OHM-CV) is a research initiative aimed at improving the understanding and modeling of the Mediterranean intense rain events that frequently result in devastating flash floods in southern France. A primary objective is to bring together the skills of meteorologists and hydrologists, modelers and instrumentalists, researchers and practitioners, to cope with these rather unpredictable events. In line with previously published flash-flood monographs, the present paper aims at documenting the 8–9 September 2002 catastrophic event, which resulted in 24 casualties and an economic damage evaluated at 1.2 billion euros (i.e., about 1 billion U.S. dollars) in the Gard region, France. A description of the synoptic meteorological situation is first given and shows that no particular precursor indicated the imminence of such an extreme event. Then, radar and rain gauge analyses are used to assess the magnitude of the rain event, which was particularly remarkable for its spatial extent with rain amounts greater than 200 mm in 24 h over 5500 km2. The maximum values of 600–700 mm observed locally are among the highest daily records in the region. The preliminary results of the postevent hydrological investigation show that the hydrologic response of the upstream watersheds of the Gard and Vidourle Rivers is consistent with the marked space–time structure of the rain event. It is noteworthy that peak specific discharges were very high over most of the affected areas (5–10 m3 s−1 km−2) and reached locally extraordinary values of more than 20 m3 s−1 km−2. A preliminary analysis indicates contrasting hydrological behaviors that seem to be related to geomorphological factors, notably the influence of karst in part of the region. An overview of the ongoing meteorological and hydrological research projects devoted to this case study within the OHM-CV is finally presented

Definition and characterization of localised meningitis epidemics in Burkina Faso: a longitudinal retrospective study

<p>Abstract</p> <p>Background</p> <p>The epidemiology of meningococcal meningitis in the African meningitis belt is characterised by seasonality, localised epidemics and epidemic waves. To facilitate research and surveillance, we aimed to develop a definition for localised epidemics to be used in real-time surveillance based on weekly case reports at the health centre level.</p> <p>Methods</p> <p>We used national routine surveillance data on suspected meningitis from January 2004 to December 2008 in six health districts in western and central Burkina Faso. We evaluated eight thresholds composed of weekly incidence rates at health centre level for their performance in predicting annual incidences of 0.4%and 0.8% in health centre areas. The eventually chosen definition was used to describe the spatiotemporal epidemiology and size of localised meningitis epidemics during the included district years.</p> <p>Results</p> <p>Among eight weekly thresholds evaluated, a weekly incidence rate of 75 cases per 100,000 inhabitants during at least two consecutive weeks with at least 5 cases per week had 100% sensitivity and 98% specificity for predicting an annual incidence of at least 0.8% in health centres. Using this definition, localised epidemics were identified in all but one years during 2004-2008, concerned less than 10% of the districts' population and often were geographically dispersed. Where sufficient laboratory data were available, localised epidemics were exclusively due to meningococci.</p> <p>Conclusions</p> <p>This definition of localised epidemics a the health centre level will be useful for risk factor and modelling studies to understand the meningitis belt phenomenon and help documenting vaccine impact against epidemic meningitis where no widespread laboratory surveillance exists for quantifying disease reduction after vaccination.</p

Molecular Characteristics and Epidemiology of Meningococcal Carriage, Burkina Faso, 2003

Meningococcal serogroups are genetically diverse and short-lived in the African meningitis belt

Characteristics and conditions of production of transient luminous events observed over a maritime storm

International audienceOn the night of 15/16 November 2007, cameras in southern France detected 30 transient luminous events (TLEs) over a storm located in the Corsican region (France). Among these TLEs, 19 were sprites, 6 were halos, and 5 were elves. For 26 of them, a positive “parent” cloud‐to‐ground lightning (P+CG) flash was identified. The peak current of the P+CG flashes for the sprites had an average value of 63 kA and had a maximum value of 125 kA. The flashes for the halos and the elves had average values of 272 and 351 kA, respectively, and they had maximum values of 312 and 384 kA, respectively. No TLEs were detected after negative CG flashes with very large peak currents. Among the 26 P+CG flashes, 23 were located in a stratiform region with reflectivity values lower than 45 dBZ. The CG flashes in this region were classified into two groups according to the time interval separating them from the following flash: one group with values less than 2 s and one with values greater than 2 s. About 79% of all CGs were produced in a sequence of at least two flashes less than 2 s apart. For 65.5% of the sequences, the first flash was positive with an average peak current of 73 kA, while the later +CG flashes in a sequence had much lower peak currents. Several triangulated sprites were found to be shifted from their P+CG flashes by about 10 to 50 km and preferentially downstream. The observations suggest that the P+CG flashes can initiate both sprites and other CG flashes in a storm

Meningitis Dipstick Rapid Test: Evaluating Diagnostic Performance during an Urban Neisseria meningitidis Serogroup A Outbreak, Burkina Faso, 2007

Meningococcal meningitis outbreaks occur every year during the dry season in the “meningitis belt” of sub-Saharan Africa. Identification of the causative strain is crucial before launching mass vaccination campaigns, to assure use of the correct vaccine. Rapid agglutination (latex) tests are most commonly available in district-level laboratories at the beginning of the epidemic season; limitations include a short shelf-life and the need for refrigeration and good technical skills. Recently, a new dipstick rapid diagnostic test (RDT) was developed to identify and differentiate disease caused by meningococcal serogroups A, W135, C and Y. We evaluated the diagnostic performance of this dipstick RDT during an urban outbreak of meningitis caused by N. meningitidis serogroup A in Ouagadougou, Burkina Faso; first against an in-country reference standard of culture and/or multiplex PCR; and second against culture and/or a highly sensitive nested PCR technique performed in Oslo, Norway. We included 267 patients with suspected acute bacterial meningitis. Using the in-country reference standard, 50 samples (19%) were positive. Dipstick RDT sensitivity (N = 265) was 70% (95%CI 55–82) and specificity 97% (95%CI 93–99). Using culture and/or nested PCR, 126/259 (49%) samples were positive; dipstick RDT sensitivity (N = 257) was 32% (95%CI 24–41), and specificity was 99% (95%CI 95–100). We found dipstick RDT sensitivity lower than values reported from (i) assessments under ideal laboratory conditions (>90%), and (ii) a prior field evaluation in Niger [89% (95%CI 80–95)]. Specificity, however, was similar to (i), and higher than (ii) [62% (95%CI 48–75)]. At this stage in development, therefore, other tests (e.g., latex) might be preferred for use in peripheral health centres. We highlight the value of field evaluations for new diagnostic tests, and note relatively low sensitivity of a reference standard using multiplex vs. nested PCR. Although the former is the current standard for bacterial meningitis surveillance in the meningitis belt, nested PCR performed in a certified laboratory should be used as an absolute reference when evaluating new diagnostic tests