A Comparison Study of Bias-Corrected Model Dust Particle Size Distributions with In Situ Measurements

Desert dust particles in the atmosphere can directly scatter and absorb radiation during their lifetimes. Size distribution of dust varies temporally and spatially, partly due to longer lifetimes of smaller particles as they settle more slowly. An overestimation in emitted size distribution in clay size range and an underestimation in coarse size range by current general circulation models (GCMs) have led to uncertainties in aerosol radiative effect because size determines the wavelengths at which particles produce the greatest radiative effect. One cause is the imprecise parametrization of non-linear small-scale processes that large-scale GCMs cannot resolve. An analytical framework was previously developed to minimize the resulting uncertainties by imposing an experimental constraint on the globally-averaged emitted dust size distribution. Here we validate this framework by comparing model outputs under this constraint with in situ size distribution data. Six GCMs, including CESM (Community Earth System Model), CNRM (Centre National de Recherches Météorologiques), GEOS-Chem (Goddard Earth Observing System Chemical Model), GISS GCM (Goddard Institute for Space Studies General Circulation Model), IMPACT (International Model for Policy Analysis of Agricultural Commodities and Trade), and WRF-Chem (Weather Research and Forecasting model coupled with Chemistry), were employed to generate dust size distributions as a function of location, season, and height. In addition, a statistical method was applied to the above models to minimize errors due to individual model assumptions. Over 20 sets of measurements from African and Asian source regions were used for location-based comparison. Quantitative and qualitative results show that the bias-corrected model size distributions reproduce the measurements with less error than the original model estimates.