Simulation of dust aerosol radiative feedback using the Global Transport Model of Dust: 1. Dust cycle and validation

We have developed a Global Transport Model of Dust (GMOD) within a general circulation model, using comprehensive parameterizations of the emission and deposition processes from Wang et al. (2000). These parameterizations are modified to match the surface conditions and meteorological fields of the climate model. A 20-year simulation from the dust model predicts an average dust emission of 1935 +/- 51 Tg a(-1) and a global dust burden of 27.8 +/- 0.8 Tg for particles whose radii are smaller than 10 mu m. Comparisons with observations show that the GMOD reproduces reasonably well dust concentrations (mean bias MB of -0.67 mu g m(-3), normalized mean bias NMB of -8.0%, correlation coefficient of 0.96 at 18 sites), logarithmic total deposition (-0.62 g m(-2) a(-1), -36.0%, 0.84 at 251 sites), and aerosol optical thickness (-0.04, -26.7%, 0.80 at 16 sites). The simulated dust particle size distribution is consistent with observations; both have a volume median radius in the range 1.0-4.0 mu m. We examine the temporal variation of dust transport on different timescales. The simulated interannual variability is small, but the seasonal variation is quite large in the Sahara Desert and central Asia. We pay special attention to the diurnal variation of dust; both observations and simulations show that dust mobilization is more active during the local daytime than nighttime. On a global and annual mean basis, the simulated ratio of the daytime maximum uplift to the nighttime minimum is 75. Both the dust burden and dry deposition of dust show a similar diurnal cycle peaking in the late afternoon.