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Skonieczny C.,French National Center for Scientific Research | Bory A.,French National Center for Scientific Research | Bout-Roumazeilles V.,French National Center for Scientific Research | Abouchami W.,Max Planck Institute for Chemistry | And 11 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2011

Mineral dust deposits were collected at Mbour, Senegal, throughout the spring of 2006 and especially during the well-documented March 7-13 large Saharan dust outbreak. During this 7-day period, significant changes in mass flux, grain-size, clay mineralogy and Sr and Nd isotopic compositions were recorded, indicating distinct provenances for the dust transported and deposited during and outside the event. All these terrigenous proxies, as well as freshwater diatom taxa, also showed significant temporal variations during the outbreak, implying contributions from at least two different provenance regions. Tri-dimensional back-trajectories and satellite imaging enabled us to link those distinct signatures to regions increasingly to the southeast within a large area covering Mauritania, Mali and southern Algeria, identified by the Total Ozone Mapping Spectrometer (TOMS) as the main source of the prominent winter/spring plume over the tropical Atlantic. The multiproxy characterization of the March 7-13 dust fall therefore enables us to typify the terrigenous signature of two different regions supplying dust off West Africa, and provide valuable clues for the interpretation of Northeastern Tropical Atlantic Ocean dust sedimentary records in terms of changes in provenance regions and transport systems. Additionally, because dust deposition data are scarce, flux and grain size data obtained in this study, among other parameters such as clay assemblages, provide important constraints for atmospheric transport models and dust deposition budget estimates in this area. © 2011 by the American Geophysical Union.

Kaly F.,LTI | Marticorena B.,LISA | Chatenet B.,LISA | Rajot J.L.,LISA | And 12 more authors.
Atmospheric Research | Year: 2015

The "Sahelian belt" is known as a region where mineral dust content is among the highest in the world. In the framework of the AMMA international Program, a transect of three ground based stations, the "Sahelian Dust Transect" (SDT), has been deployed in order to obtain quantitative information on the mineral dust content over the Sahel. These three stations: Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) are aligned at 13°N along the east-west main pathway of the Saharan and Sahelian dust toward the Atlantic Ocean. The SDT provides a set of aerosol measurements and local meteorological parameters to describe and understand the mechanisms that control the temporal and regional variability of mineral dust content in these regions. In this work we analyze the seasonal and diurnal variability of the dust concentrations over the period 2006-2010. The analysis of the dust concentrations measured between 2006 and 2010 confirmed a regional seasonal cycle characterized by a maximum in the dry season, with median concentration ranging from 205μgm-3 at Banizoumbou to 144μgm-3 at M'Bour, and a minimum (11-32μgm-3) in the wet season. The five year data set allowed the quantification of the variability of the monthly concentrations. The range between the percentiles 75 and 25 varies linearly with the median concentration: it is of the same order than the median value in M'Bour, 17% slightly higher in Cinzana and 50% higher in Banizoumbou. The range between the accepted maximum and minimum is also correlated with the median value, with slopes ranging from 14 in Banizoumbou to 7 in M'Bour. Part of the variability of the concentration at the monthly scale is due to interannual variability. Extremely high or low monthly concentration can be recorded that significantly impacts the five year median concentration and its range. Compared to the 3-year data set analyzed by Marticorena et al. (2010), the two additional years used in this work appear as the less dusty year (2009) and one of the dustier years (2010).The sampling time step and the high recovery rates of the measurement stations allowed to investigate the diurnal cycle of the dust concentration for the first time. During the dry season, the hourly median concentrations range from 80 to 100μgm-3 during the night to 100-160μgm-3 during the day-time maximum. The diurnal cycle of the PM10 concentrations is phased with the diurnal cycle of the surface wind speed and thus modulated by the interactions between the nocturnal lower level jet (NLLJ) and the surface boundary layer. The NLLJ appears as a major agent to transport Saharan dust toward the Sahel. During the wet season, the median PM10 concentrations are maximum at night-time (<50μgm-3). The night-time concentrations are associated with a large range of variability and coincide with the periods of higher occurrence of meso-scale convective systems. The amplitude of the diurnal cycle is of the order of 60μgm-3 in the dry season and 20μgm-3 in the wet season. Both in the dry and in the wet season, despite a month to month variability of the daily dust concentration, a typical diurnal pattern has been established suggesting that this temporal pattern is mainly driven by local meteorological conditions. © 2015 Elsevier B.V.

Alory G.,Toulouse 1 University Capitole | Delcroix T.,Toulouse 1 University Capitole | Techine P.,Toulouse 1 University Capitole | Techine P.,French National Center for Scientific Research | And 16 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2015

Sea Surface Salinity (SSS) is an essential climate variable that requires long term in situ observation. The French SSS Observation Service (SSS-OS) manages a network of Voluntary Observing Ships equipped with thermosalinographs (TSG). The network is global though more concentrated in the tropical Pacific and North Atlantic oceanic basins. The acquisition system is autonomous with real time transmission and is regularly serviced at harbor calls. There are distinct real time and delayed time processing chains. Real time processing includes automatic alerts to detect potential instrument problems, in case raw data are outside of climatic limits, and graphical monitoring tools. Delayed time processing relies on a dedicated software for attribution of data quality flags by visual inspection, and correction of TSG time series by comparison with daily water samples and collocated Argo data. A method for optimizing the automatic attribution of quality flags in real time, based on testing different thresholds for data deviation from climatology and retroactively comparing the resulting flags to delayed time flags, is presented. The SSS-OS real time data feed the Coriolis operational oceanography database, while the research-quality delayed time data can be extracted for selected time and geographical ranges through a graphical web interface. Delayed time data have been also combined with other SSS data sources to produce gridded files for the Pacific and Atlantic oceans. A short review of the research activities conducted with such data is given. It includes observation-based process-oriented and climate studies from regional to global scale as well as studies where in situ SSS is used for calibration/validation of models, coral proxies or satellite data. © 2015 Elsevier Ltd.

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