MODELING THE ATMOSPHERIC DUST CYCLE .2. SIMULATION OF SAHARAN DUST SOURCES

A soil-derived dust emission scheme has been designed in order to prov ide simulation of mineral dust sources for atmospheric transport model s [Marticorena and Bergametti, 1995]. This physical scheme considers t he influence of surface features to compute the erosion threshold and the intensity of the dust emissions. It has been validated by comparis on with relevant experimental data. However, it was necessary to exten d its applicability and to test its capability to reproduce dust emiss ions over large arid areas. Specific methods have been developed to de termine the parameters required by the dust production model for large -scale applications. The surface features (dimensions of the roughness elements and soil mineralogy) and the wind velocity allow the computa tion of the roughness lengths of the surface, the size distribution of the erodible soils, and the wind friction velocity. A map of these su rface characteristics has been established for the western part of the Sahara. This map coupled to the Europan Center for Medium-Range Weath er Forecast (ECMWF) surface wind fields are used to simulate dust emis sions in this desert region. The simulated emissions have been compare d to the Infrared Difference Dust Index (IDDI), determined by means of the Meteosat thermal infrared imagery. The simulated dust event frequ encies are in good agreement with those observed by satellite. The com parison between the simulated fluxes and the satellite observations fo r 3 months of the year 1991 has revealed a linear relationship between the logarithm of the simulated flux and the IDDI. The annual and mont hly dust emissions for 1991 and 1992 have been estimated and compared to those established by d'Almeida [1986]. Both the frequencies and the intensities of the emissions are well reproduced by the model associa ted with the surface features map.