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Scaling of Dust Flux With Friction Velocity: Time Resolution Effects
Author(s) -
Dupont S.
Publication year - 2020
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2019jd031192
Subject(s) - intermittency , scaling , aeolian processes , flux (metallurgy) , wavelet , resolution (logic) , shear velocity , turbulence , covariance , eddy covariance , momentum (technical analysis) , mechanics , physics , mathematics , geology , materials science , statistics , geometry , geomorphology , ecology , finance , artificial intelligence , ecosystem , computer science , economics , metallurgy , biology
The intermittency of aeolian soil erosion has motivated studies to extend to small time resolution (less than 15–30 min) the scaling property of erosion fluxes with the friction velocityu * . However, common methods used to estimateu *such as the law of the wall or the eddy covariance are only valid for stationary conditions, that is, long periods of 15–30 min. Unlike these methods, the wavelet transform method is applicable for nonstationary conditions. Here, this method is used to investigate the scaling property of the dust fluxF w dwithu *at 1‐min and 10‐s resolutions, during erosion events. At 15‐min resolution,u *andF w destimated from the wavelet transform are identical to those obtained by eddy covariance. At smaller resolution,u *andF w dexhibit strong fluctuations around their 15‐min trend, reflecting the nonstationarity of the flow and the intermittency of dust emission, respectively. While the 15‐min resolutionF w dappears as correlated withu *as with the mean wind speed U , with decreasing resolution,F w dbecomes less correlated withu *but still significantly correlated with U . Our results suggest thatu *is a suitable scaling parameter ofF w dover usual 15‐ to 30‐min periods with the advantage of being height independent compared to U . However, at small time resolution, U becomes more relevant to scaleF w d , the surface friction velocity becoming hardly accessible due to the absence of a constant momentum flux layer. Our study demonstrates the suitability of the wavelet transform to estimate dust fluxes at small time resolution or during nonstationary events.