资源环境科技发展态势分析平台

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 velocity u(*). However, common methods used to estimate u(*) 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 flux Fwd with u(*) at 1-min and 10-s resolutions, during erosion events. At 15-min resolution, u(*) and Fwd estimated from the wavelet transform are identical to those obtained by eddy covariance. At smaller resolution, u(*) and Fwd exhibit strong fluctuations around their 15-min trend, reflecting the nonstationarity of the flow and the intermittency of dust emission, respectively. While the 15-min resolution Fwd appears as correlated with u(*) as with the mean wind speed U, with decreasing resolution, Fwd becomes less correlated with u(*) but still significantly correlated with U. Our results suggest that u(*) is a suitable scaling parameter of Fwd over 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 scale Fwd, 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.