Microlidar observations of biomass burning aerosol over Djougou (Benin) during African Monsoon Multidisciplinary Analysis Special Observation Period 0: Dust and Biomass-Burning Experiment

Abstract : Microlidar observations have been performed at the Djougou-Nangatchori site in northern Benin during the African Monsoon Multidisciplinary Analysis (AMMA) Special Observation Period 0 in the dry season, combined with the Dust and Biomass-Burning Experiment (DABEX) from mid-January to mid-February 2006. During the dry season, the Djougou area is a region where biomass burning aerosols are heavily produced from agriculture fires. The aerosol vertical distribution is also controlled by dynamics, and the penetration of the winter monsoon flux to the north and northern winds bringing mineral dust to the South leads to a frontal discontinuity location close to Djougou latitude. During the early dry season, the aerosol vertical distribution was observed to be structured in two layers, the lower being the boundary layer reaching altitudes up to 2 km and the upper one corresponding to the trade wind layer extending up to 5 km. Lidar data are used to retrieve the time evolution and vertical profile of extinction and discuss transport processes during the period analyzed. As the monsoon flux during the dry season is steadily progressing to the north but also moving back and forth according to shorter timescale forcings, biomass burning particles are transported from the boundary layer into the upper troposphere. This transport has a strong impact on the distribution of aerosol particles on the vertical, and extinction values larger than 0.3 km−1 have been retrieved at altitudes close to 3 km. A particular event of biomass burning air mass outbreak associated with a synoptic forcing is studied, where satellite observations are used to discuss observations of biomass burning particles over Djougou and at the regional scale.