The 2020 Summer Extreme Dust Event: Effects of the Albedo Drag Partition on the FENGSHA Dust Emission Parameterization in GEFS-Aerosol

Abstract:

Aerosols have both direct and indirect effects on meteorology, atmospheric chemistry, human health, and ultimately the global energy budget with dust being a major contributor to the atmospheric aerosol burden. A great effort has been made to characterize the sources and mobilization of dust, however, current models still show large uncertainty as the modeling of mineral dust in the atmosphere is complex. The FENGSHA dust emission model, implemented into the operational NOAA National Air Quality Forecast Capability (NAQFC), and the new Global Ensemble Forecast System with Aerosols (GEFS-Aerosols), is a flexible emission model capable of predicting dust emissions across forecast scales. In this study, we focus on the summer 2020 extreme dust event that originated in northern Africa and affected the Caribbean and North America. Multiple dust events were active within this region and the plumes mixed as they were transported creating a complex and massive dust event. The planned operational version of GEFS-Aerosols adequately captured the transport and spatial pattern of the dust plumes, while underpredicting their magnitude. The underprediction is thought to be due to an overestimation of the drag partition over the dust sources creating an artificially high threshold friction velocity. Therefore a new drag partition based on the MODIS Black-Sky Albedo is implemented into FENGSHA. A comparison is done between the traditional, z0 based, drag partition and dynamic, albedo based, drag partition and its effect on the FENGSHA dust emission scheme. Results show that the albedo drag partition better captured the spatial pattern of the extreme event as well as the magnitude of the dust plume transported across the ocean.