Characteristics of Turbulence Over the Semi-Fixed Desert Area in North of Xinjiang, China

Abstract

As the largest fixed and semi-fixed desert in China, the Gurbantunggut Desert undergoes a long period of snow cover in the winter and the rapid growth of ephemeral plants in the spring, presenting obvious seasonal changes in the underlying desert surface type, which can lead to variation in the turbulence of the near-surface boundary layer turbulence over the desert. In this study, gradient tower data and eddy covariance data from 2017 were analyzed to investigate the turbulence characteristics of the different surface boundary layers in the hinterland of the Gurbantunggut Desert. The results indicate that stable atmospheric conditions in the desert occur exclusively during the early morning and at night in the desert, and the onset and duration of this stable state varies seasonally. Two regimes of intermittent turbulence occur during the night; a weak turbulent regime that occurs when the wind speed is less than the threshold and a strong turbulent regime when the wind speed exceeds the threshold. The sensible heat flux and turbulent kinetic energy of the desert vary on a diurnal basis, with a single peak appearing at approximately 12:00 local standard time (LST). These parameters follow a seasonal pattern of summer > spring > autumn > winter in terms of the magnitude. The mean turbulence intensities of the along-wind, crosswind and vertical wind are 0.5, 0.47, and 0.14, respectively, with I u > I v > I w . The turbulence intensity is nearly constant when the wind velocity exceeds 6 m·s -1 . The normalized standard deviation of the wind velocity components (σ u , σ v and σ w ) generally satisfies a 1/3 power-law relation.