Characteristics of turbulence over the semi-fixed desert area north of Xinjiang, China

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 analysed 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, and different wind speed thresholds were observed at each level. These parameters follow a seasonal pattern of summer (July) > spring (April) > autumn (October) > winter (January) in terms of magnitude. The mean turbulence intensities of the along-wind, cross-wind and vertical wind are 0.5, 0.47 and 0.14, respectively, with I-u > I-v > I-w. The normalized standard deviation of the wind velocity components (sigma(u), sigma(v) and sigma(w)) generally satisfies a 1/3 power-law relation. Our results show that the night-time turbulence regime classification for the Gurbantunggut Desert strongly depends on meteorological and orographic features, and the intermittent turbulent events have the non-stationarity of the flow in common. The results can contribute to the study of land surface processes, climate change and desertification in inland arid desert areas.

Automated summary

This study investigated the turbulence characteristics of different surface boundary layers in the hinterland of the Gurbantunggut Desert, the largest fixed and semi-fixed desert in China. The results revealed the presence of stable atmospheric conditions exclusively during the early morning and at night in the desert, with two regimes of intermittent turbulence occurring during the night. Additionally, the study highlighted the seasonality and varying wind speed thresholds in the desert.