Abstract:

We present a model of the dust cycle that successfully predicts dust emissions as determined by land surface properties, monthly vegetation and snow cover, and 6-hourly surface wind speeds for the years 1982-1993. The model takes account of the role of dry lake beds as preferential source areas for dust emission; the occurrence of these preferential sources is determined by a water routing and storage model. The dust source scheme also explicitly takes into account the role of vegetation type as well as monthly vegetation cover. Dust transport is computed using assimilated winds for the years 1987-1990. Deposition of dust occurs through dry and wet deposition, where sub-cloud scavenging is calculated using assimilated precipitation fields. Comparison of simulated patterns of atmospheric dust loading to the TOMS satellite absorbing aerosol index shows the model produces realistic results from daily to interannual timescales. The magnitude of dust deposition agrees well with sediment flux data from marine sites. Emission of submicron dust from preferential source areas are required for the computation of a realistic dust optical thickness. Sensitivity studies show that Asian dust source strengths are particularly sensitive to the seasonality of vegetation cover. The explicit simulation of the dependency of dust emissions on vegetation type and cover, as well as on lake levels, is a pre-requisite to estimate dust emissions under changed climatic conditions.