Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2016-683
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
06 Dec 2016
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Seasonal cycle of desertic aerosols in West Africa: Analysis of the Coastal transition with passive and active sensors
Habib Senghor1, Éric Machu1,2, Frédéric Hourdin3, and Amadou Thierno Gaye1 1Laboratoire de Physique de l’Atmosphère et de l’Océan Siméon-Fongang (LPAO-SF), École Supérieure Polytechnique (ESP) de l’Université Cheikh Anta Diop de Dakar (UCAD), Sénégal
2Laboratoire de Physique des Océans (LPO), Institut Universitaire Européen de la Mer (IUEM), Brest, France
3Laboratoire de Météorologie Dynamique (LMD), CNRS/IPSL/UMPC, Paris, France
Abstract. The impact of desertic aerosols on climate, atmospheric processes and the environment is still debated in the scientific community. The extent of their influence remains to be determined and particularly requires a better understanding of the variability of their distribution. In this work, we studied the variability of these aerosols in West Africa using different types of satellite observations. SeaWiFS and OMI data have been used to characterize the spatial distribution of mineral aerosols from their optical and physical properties over the period 2005–2010. In particular, we focused on the variability of the transition between the West African continent and the Eastern Atlantic Ocean. Data provided by the Lidar scrolling CALIOP onboard the satellite CALIPSO (Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) for the period 2007–2013 were then used to assess the seasonal variability of the vertical distribution of desertic aerosols. We first obtained a good representation of Aerosol Optical Depth (AOD) and Single Scattering Albedo (SSA) by satellites (SeaWiFS and OMI, respectively) in comparison with AERONET estimates, both above the continent and the ocean. Dust occurrence frequency is higher in spring and boreal summer. In spring, the highest occurrences are located between the surface and 3 km above sea level, while in summer the highest occurrences are between 2 and 5 km altitude. The vertical distribution given by CALIOP also highlights an abrupt change at the coast from spring to fall with a layer of desertic aerosols confined in an atmospheric layer uplifted from the surface of the ocean. This uplift of the aerosol layer above the ocean contrasts with the winter season during which mineral aerosols are confined in the atmospheric boundary layer. Radiosondes at Dakar Weather Station (17.5° W, 14.74° N) provide basic thermodynamic variables which partially give causal relationship between the layering of the atmospheric circulation over West Africa and their aerosol contents throughout the year. A SSA increase is observed in winter and spring at the transition between the continent and the ocean. The analysis of mean NCEP winds at 925 hPa between 2000 and 2012 suggest a significant contribution of coastal sand sources from Mauritania in winter which would increase SSA over the ocean.

Citation: Senghor, H., Machu, É., Hourdin, F., and Gaye, A. T.: Seasonal cycle of desertic aerosols in West Africa: Analysis of the Coastal transition with passive and active sensors, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-683, in review, 2016.
Habib Senghor et al.
Habib Senghor et al.
Habib Senghor et al.

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Short summary
This work focus on the distribution of dust particles emitted in West Africa and having consequences on human health and marine ecosystems. The understanding of their fate requires a better understanding of the processes governing their variability. Using satellite observations and ground measurements, we present the seasonality of their distribution and explain the processes responsible for this distribution as well as their transition from the African continent towards the Atlantic ocean.
This work focus on the distribution of dust particles emitted in West Africa and having...
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