Sensitivity of Atmospheric Soil Dust and Radiative Forcing by Dust to the Emitted Dust Size Distribution in GISS ModelE2.1

Soil/Mineral dust emitted from deserts and semi-arid source regions is a major atmospheric aerosol that affects weather, climate, and biogeochemical cycles in multiple ways. Despite decades of measurement and modeling efforts, the magnitude and variability of the dust cycle and its interactions in weather and climate are still very uncertain. One source of the uncertainty is the poorly constraint size distribution of the dust aerosol particles emitted from the parent soils. We carry out climatological simulations with NASA GISS Earth system model ModelE2.1, using different assumptions for the emitted size distribution of dust aerosols. These include the currently used default size distribution in the model with a silt to clay ratio optimized toward AERONET measurements and a mass distribution in the silt size range that is constant with the logarithm of the particle diameter, a size distribution that is based on the Aerosol Intercomparison project (AeroCom), and a size distribution that is derived from Brittle Fragmentation Theory (BFT) augmented with large particle emission. We study the sensitivity of the simulated mean dust cycle and estimates of the radiative forcing by dust to the assumptions on the emitted dust size distribution. We also discuss how the results need to be analyzed in the context of the calibration of the simulated dust cycle in the model, which is required to avoid a large mismatch with data from observations.