Development of a MODIS/VIIRS Base Estimation of Lateral Cover for Low Vegetation: Applications to Dust and Land Surface Modeling within NOAA’s Air Composition Forecasts

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. One of the key parameters to model aeolian emissions within weather, climate, and air quality models is the drag partition (the ratio of the momentum stress directly on the surface to that of the boundary layer stress). Previous studies have used in situ and/or remote sensing scatterometer measurements to quantify the small-scale land-surface momentum roughness (e.g., Greeley et al., 1997; Roujean et al., 1997; Marticorena et al., 2004; Prigent et al., 2005, 2012), especially over arid desert regions over which rocks, pebbles, and gravel dominate the roughness. There have recently been several attempts to update the drag partition definition to include the effects of both rocky terrain and vegetation within dust models (e.g. Chappel and Webb 2016, Leung et al (2023,2024)). Furthermore, Marticorena et al. (2004) and King et al. (2005) showed that using Bidirectional Reflectance Distribution Function (BRDF) measurements from the Polarization and Directionality of the Earth’s Reflectances (POLDER) satellite instrument the lateral cover and therefore roughness can be derived using both the isometric and geometric parameters. Within this work the BRDF algorithm is adapted to VIIRS and MODIS measurements, which allow for a longer time series as well as higher spatial and temporal resolution. The derived lateral cover is adapted to the FENGSHA dust emission scheme following the Raupach (1993) and Darmenova (2011) formulations and implemented into the UFS-GOCART model, which is used for the upcoming GEFSv13 operational NOAA implementation. The effects of the new drag partition on dust simulations are compared to baselines of the Chappel and Webb (2016) and Prigent et al (2012) methods are shown and compared to aeronet and satellite optical depth measurements as well as in-situ tower measurements of the momentum roughness length within low vegetated areas. Drag partition and later cover long term time series are also presented to demonstrate the evolving change and contribution that the land surface representation in low vegetated areas can have on the overall dust load within Earth’s atmosphere.