Online simulations of mineral dust aerosol distributions: Comparisons to NAMMA observations and sensitivity to dust emission parameterization

A key uncertainty within Earth system modeling lies in the parameterization of the emission process for mineral aerosols, where emission scheme choice can have implications for emitted dust fluxes. For our study, we include versions of dust emission schemes from the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) and Dust Entrainment and Deposition (DEAD) models in the new NASA Goddard Earth Observing System version 4 model, to identify differences in simulated dust distributions caused by varying the emission scheme. The GOCART and DEAD schemes differ in their parameterization of the mobilization process, including their sensitivity to meteorological variables and the determination of the emitted particle size distribution. We focus on Saharan dust events during the NASA African Monsoon Multidisciplinary Analyses field campaign (August-September 2006) to compare with in situ, ground-based, and remote sensing observations. We find that the emission schemes produce comparable aerosol optical thickness and vertical extinction profiles, and their distributions compare well with observations from the space-based MODIS, OMI, MISR, and CALIPSO sensors, and the airborne LASE lidar. Neither emission scheme does especially well at capturing the variability or magnitude of specific dust events over the source region when compared to AERONET and MISR observations, but both improve downwind of the dust sources. Despite the similarities in the optical comparisons, the schemes differ in mass loadings owing to differences in their emitted dust particle size distributions over the source region. Our findings suggest that emission scheme choice for general circulation models is important only over the source region, where the emitted particle size distributions and corresponding mass budgets of emissions are influenced.