ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-3881-2009 Size resolved dust emission fluxes measured in Niger during 3 dust storms of the AMMA experiment Sow M. 1 3 Alfaro S. C. 1 Rajot J. L. 3 Marticorena B. 2 Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR CNRS/INSU 7583, IPSL, Université de Paris 12-Val de Marne, Créteil, France Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR CNRS/INSU 7583, IPSL, Université de Paris 7-Denis Diderot, Paris, France Institut de Recherche pour le Développement (IRD), UMR IRD 211 Bioemco, Niamey, Niger 15 06 2009 9 12 3881 3891 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/3881/2009/acp-9-3881-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/3881/2009/acp-9-3881-2009.pdf

During the 2006 and 2007 special observing periods of the African Monsoon Multidisciplinary Analysis campaign an original experimental system has been implemented in Banizoumbou (Niger) for measuring the size-resolved dust emission flux in natural conditions and documenting the possible influence of wind speed on its size distribution. The instrumental set-up, associated methodology, and the quality tests applied to the data set are described before the results acquired during 2 events of the Monsoon type and 1 of the convective type are analyzed in detail. In good agreement with the theory of sandblasting, it is found in all cases that saltation must take place for a vertical emission flux to be detected. During a particular erosion event, the magnitude of the vertical flux is controlled by the surface roughness, which conditions the saltation threshold, and by the wind friction velocity. The dust flux released by the high energy convective event is also found to be much richer in very fine (&lt;2 &micro;m) particles than those of the relatively moderate Monsoon event, which shows that aerodynamic conditions definitely influence the initial size distribution of the erosion flux as previously suggested by wind tunnel experiments. However, the size distribution of the dust released by a given event is fairly constant and insensitive to even relatively important variations of <i>u*</i>. This is interpreted as a possible result of the rather long duration (15 min) over which wind fluctuations must be averaged for computing <i>u*</i>, which could make it an inadequate parameter for representing the very short response-time physical processes that are at the origin of fine dust emission at the measurement sites.

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