Simulations of spatial variability in particle-size emissions during wind erosion events

Abstract

This study simulates how spatial variations in particle-size emissions from a playa affect bulk and size-resolved dust concentration profiles during two contrasting wind erosion events (a small local and a large regional event) in the Channel Country, Lake Eyre Basin, Australia. The regional event had higher dust concentration as a result of stronger frontal winds and higher erodibility across the playa. For each event, two emission scenarios are simulated to determine if measured size-resolved dust concentration profiles can be explained by spatial variability in source area emissions. The first scenario assumes that particle-size emissions from source areas occur at a uniform rate, while the second scenario assumes that particle-size emissions vary between and within source areas. The uniform emission scenario, reproduced measured bulk dust concentration profiles (R2=0 93 regional and R2=0 81 local), however simulated size-resolved dust concentration profiles had poor statistical fits to measured size-resolved profiles for each size class (the highest were R2=0 5 regional and R2=0 3 local). For the differential particle-size emission scenario, the fit to the measured bulk dust concentration profiles is improved (R2=0 97 regional and R2=0 83 local). However, the fit to the size-resolved profiles improved dramatically, with the lowest being R2=0 89 (regional) and R2=0 80 (local). Particle-size emission models should therefore be tested against both bulk and size-resolved dust concentration profiles, since if only bulk dust concentration profiles are used model performance may be over-stated. As the source areas in the first 90m upwind of the tower were similar for both events, the percentage contributions of each particle-size class to total emissions can be compared. The contribution of each particle-size class was similar even though the wind speed, turbulence and dust concentrations were significantly different; suggesting that the contribution of each particle-size to the total emitted dusts is not related to wind speed and turbulence.