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

Abstract

ABSTRACTThis 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 90 m 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. Copyright © 2012 John Wiley & Sons, Ltd.