Characteristics of summer turbulence and analysis of ozone sounding in the hinterland of the Taklimakan Desert, Northwest China
摘要
Due to the arid and sandy surface of the Taklimakan Desert (TD) in China, the turbulence structure and vertical distribution of ozone exhibit unique and complex characteristics. However, few studies have focused on these issues. To reveal the variation characteristics of summertime atmospheric turbulence and ozone concentration over the TD, we conducted joint detection experiments in July 2016 and July 2021 at Tazhong in the hinterland of the TD using an eddy covariance detection system, a GPS (Global Positioning System) sounding system, and a meteorological gradient tower. Using methods such as statistical analysis, nonlinear fitting, and Fast Fourier Transform, this study analyzed and processed parameters including temperature, relative humidity, wind speed, turbulence parameters, turbulence spectra, and ozone concentration. The high average temperature is accompanied by low relative humidity over the TD, showing a negative correlation between the two. The temperature of the 10.0-cm-deep sand layer lags the near-surface air temperature by nearly 4 h. From 09:30 to 21:00 (Beijing Time), under conditions where the sensible heat flux is positive but stability parameter (z/L, where z is the height and L is the Obukhov length) is negative, the atmosphere is heated by the land surface, with the occurrence of unstable stratification; however, the conditions are the opposite (sensible heat flux is negative and z/L is positive) after 22:00, which are accompanied with the cooling of the surface radiation, occurrence of temperature inversion in the lower atmosphere, and stable stratification. A positive correlation is identified between the diurnal variation of turbulent kinetic energy (TKE) and the atmospheric boundary layer (ABL) height, with significant contributions from both the buoyancy and shear terms during the daytime. Under unstable stratification, the normalized standard deviations of the three-dimensional wind speed, temperature, and humidity conform to the Monin–Obukhov Similarity Theory (MOST). As the stability parameter z/L transitions from strongly unstable to strongly stable, the energy of the dimensionless turbulent velocity spectra gradually decreases and conforms to the −2/3 power law within the inertial subrange. In the hinterland of the TD, the summertime tropospheric ozone concentration remains below approximately 0.70×10−6 (volume concentration). Above the troposphere, within the range of 16,500.0–30,000.0 m, a significant increasing trend is identified in the ozone concentration with altitude. At an altitude of 30,000.0 m, the maximum ozone concentration can reach up to 7.50×10−6. The research findings provide both theoretical and data foundations for future in-depth studies of turbulent motion and ozone concentration distribution in the TD, as well as in the similar areas around the world.