New insights into dust aerosol entrainment mechanisms from satellite/ground-based data, climate modeling, and wind-tunnel experiments
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Atmospheric dust aerosols have implications for Earth’s radiation budget, biogeochemical cycles, hydrological cycles, human health, and visibility. Currently, there is a considerable mismatch between climate model simulations and observations in representing the dust cycle in terms of emission, transport, and deposition. This mismatch is related partly to our inadequate understanding of the complex dust emission processes and partly to the way these processes are represented in climate models. In this work, we examine these problems from various perspectives with an interdisciplinary approach by integrating wind-tunnel experiments, geomorphological mapping, satellite observations, land surface modeling, atmospheric reanalysis, and fully coupled earth system modeling. The primary science contributions of this work are summarized here. First, we developed a detailed regional land cover map of the dust belt, the Middle East and North Africa. The developed map can be integrated in any regional dust models for better representing the spatial variation in dust source erodibility. We also developed a new observation-based soil erodibility map in global scale based on the correlation between reanalysis surface winds and satellite-observed aerosol optical depth data (AOD). Second, we integrated the developed observation-based erodibility map into the Community Earth System Model (CESM) and evaluated CESM’s performance in simulating mineral dust emission over the dust belt. Results show that the new erodibility map improves dust simulations in terms of AOD/dust optical depth (DOD) and the CESM captures large scale dust storms reasonably well when the winds are nudged towards ERA-Interim reanalysis data. Third, we conducted wind tunnel experiments and explored some of the lesser understood physical mechanisms of dust emission in sandblasting and direct aerodynamic entrainment. Results indicate that surface roughness can control dust emission in direct aerodynamic entrainment and that dust emission by direct aerodynamic entrainment can be significant under certain conditions compared to sandblasting. Lastly, we develop a principal component analysis based technique to extract locally mobilized dust component from the AOD data, which otherwise represent a mixture of several aerosol types and advected dust/aerosols.