Temporal variability of mineral dust concentrations over West Africa: analyses of a pluriannual monitoring from the AMMA Sahelian Dust Transect
1LISA, Universités Paris Est-Paris Diderot-Paris 7, UMR 7583, Créteil, France
2IRD – UR 176 SOLUTIONS, Niamey, Niger
3IRD – UMR 211 Bioemco, Niamey, Niger
4IER – SRAC, Bamako, Mali
5IRD – Dakar, Senegal
Abstract. The Sahelian belt is known to be a region where the mineral dust content is among the highest observed on Earth. In the framework of the AMMA (African Monsoon Multidisciplinary Analysis) International Program, a transect of 3 ground based stations, the "Sahelian Dust Transect" (SDT), has been deployed in order to obtain quantitative information on the mineral dust content and its variability over the Sahel. The three stations, namely Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) are aligned around 14° N along the east-west main pathway of the Saharan and Sahelian dust towards the Atlantic Ocean.
We discuss data collected between January 2006 and December 2008 to investigate the main characteristics of the mineral dust concentration over West Africa and their connection with the dominant meteorological situations. The succession of the dry season during which the Sahel is under the influence of the dry Harmattan wind and the wet season induced by the entrance of the monsoon flow is clearly identified from the basic meteorological parameters (air temperature and moisture, wind direction). Atmospheric dust concentrations at the three stations exhibit a similar seasonal cycle, with a monthly maximum during the dry season and a minimum occurring during the rainy season, indicating that the general pattern of dust concentration is similar at regional scale. This seasonal cycle of the dust concentrations is not phased with the seasonal cycle of surface wind velocity suggesting that it is mainly controlled by Saharan dust transport. A decrease in the dust concentration is observed when moving from Niger to Senegal. However, local dust emissions induced by strong surface winds are responsible for the occurrence of extremely high daily concentrations observed at the beginning of the rainy season.