A dust outbreak episode in sub-Sahel West Africa

Wind blown dust is a major contributor to the tropospheric aerosol mass loa ding and has a significant effect on the local radiative forcing. Informati on on aerosol optical properties and their temporal and spatial distributio n is very limited. Attempts to derive such information from space, in parti cular, over land, are in a preliminary stage. Recently, information on aero sol optical properties is becoming available from ground networks within on e day from the time the observations are made. In this study, use was made of such "real-time" aerosol observations, to characterize their optical pro perties, during a heavy dust event in the sub-Sahel in January 2000. Aeroso l optical depths at all wavelengths showed a sharp increase when compared t o the average for the season, reaching values up to 3.5 at 500 nm. The Angs trom exponent was reduced from 1.2 to 0.3, and a sharp increase in the sing le-scattering albedo was found. The aerosol optical properties differed sig nificantly from climatologically available information on dust aerosols, an d therefore their timely assimilation into transport models or weather pred iction models could be of great relevance. Developments in the ways aerosol are presently observed could influence future treatment of aerosols in cli mate research.