Investigation on very large scale motions (VLSMs) and their influence in a dust storm

Based on the real-time synchronous measurements of the wind velocity, temperature, the PM10 concentration at 16 m and 47 m during a dust storm event, in which Reynolds number Re τ exceeds 6×10 6 , this study reveals the existence of the very large scale motions (VLSMs) during the stable stage both in the stream velocity and the temperature field at the two heights, whose streamwise scales reach up to 10 times the thickness of the boundary layer. The streamwise velocity and the PM10 concentration display a similar frequency corresponding to the peaks of their energy spectra, which implies that the VLSMs of streamwise flow have a significant role in dust transportation. In contrast, the salient deviations of the PM10 concentration at 47 m from the Gaussian distribution are revealed, which means that 47 m is not in the dust transportation layer, but is a region where the dust transportation layer and the outer flow intersect each other. Analysis demonstrates that the energy spectra of the PM10 concentrations at 16 m and 47 m display the “−1” scaling law feature, which has the same frequency range (0.001–0.1 Hz) as that of the wind velocity. This provides a new paradigm for the existence of the self-similarity scaling region in turbulent flow.