A field observation array for the atmospheric surface layer (ASL) was built on a dry flat bed of Qingtu Lake in Minqin (China) as the Qingtu Lake Observation Array (QLOA) site, which is similar to the Surface Layer Turbulence and Environmental Science Test (SLTEST) site in the Utah (USA) Western desert. The present observation array can synchronously perform multi-point measurements of wind velocity and temperature at different vertical and streamwise positions. In other words, three-dimensional turbulent ASL flows can be measured at the QLOA station and Reynolds numbers as high as $Re_{\unicode[STIX]{x1D70F}}\sim O(10^{6})$ can be achieved with steady wind conditions. By careful selection and pretreatment for measured data of more than 1200 h, the QLOA data have been validated to be reliable for high Reynolds number turbulent boundary layer research. Results from correlation and spectral analysis confirm that very large scale motions (VLSMs) exist in the ASL at a Reynolds number up to $Re_{\unicode[STIX]{x1D70F}}\approx 4\times 10^{6}$ . Through premultiplied spectral analysis, it is revealed that the spectral energy in the high-wavenumber region decreases with height, similar to turbulent boundary layers at low or moderate Reynolds numbers, while it increases with height in the low-wavenumber region resulting in a log–linear increase of VLSMs energy with height, which is different from turbulent boundary layers at low or moderate Reynolds numbers. The present analyses support the view that the evolution of the VLSMs cannot be fully attributed to a ‘bottom-up’ mechanism alone, and probably other mechanisms, including a ‘top-down’ mechanism, also play a role.

Long-term measurements were performed at the Qingtu Lake Observation Array site to obtain high-Reynolds-number atmospheric surface layer flow data ( $Re_{\unicode[STIX]{x1D70F}}\sim O(10^{6})$ ). Based on the selected high-quality data in the near-neutral surface layer, the amplitude modulation between multi-scale turbulent motions is investigated under various Reynolds number conditions. The results show that the amplitude modulation effect may exist in specific motions rather than at all length scales of motion. The most energetic motions with scales larger than the wavelength of the lower wavenumber peak in the energy spectra play a vital role in the amplitude modulation effect; the small scales shorter than the wavelength of the higher wavenumber peak are strongly modulated, whereas the motions with scales ranging between these two peaks neither contribute significantly to the amplitude modulation effect nor are strongly modulated. Based on these results, a method of decomposing the fluctuating velocity is proposed to accurately estimate the degree of amplitude modulation. The corresponding amplitude modulation coefficient is much larger than that estimated by establishing a nominal cutoff wavelength; moreover, it increases log-linearly with the Reynolds number. An empirical model is proposed to parametrize the variation of the amplitude modulation coefficient with the Reynolds number and the wall-normal distance. This study contributes to a better understanding of the interaction between multi-scale turbulent motions and the results may be used to validate and improve existing numerical models of high-Reynolds-number wall turbulence.

Field measurements at the Qingtu Lake Observation Array site were performed to explore the features of large scale structures relevant to very large scale motions (VLSMs) and large scale motions (LSMs) in the atmospheric surface layer during dust weather events. The three velocity components, PM10 concentrations (particles with size less than 10 μm), and sand saltation fluxes at different heights were measured synchronously. By comparing with the results in clean-air flows, the influences of sand particles on the VLSMs were investigated. The present results indicate that the streamwise turbulent kinetic energy across all scales is enhanced in the sand-laden flows. However, the energy enhancement of small-scale motions is more pronounced than that of large scale structures, resulting in a decreased energy fraction of the large scale structures in the sand-laden flows. The inclination angles of the large scale structures are found to increase with sand concentration, owing to the decreased velocity gradient. The streamwise length scale of large scale structures and the size of the most energetic turbulent structures are found to be unchanged in the sand-laden flows relative to those in the clean-air flows. This is the study on the particle-laden wall turbulence at the largest Reynolds number to date, and the results demonstrate that the dispersed tiny particles in very dilute particle–gas flows can affect the turbulence even for the large scale structures.

In this letter, the concentration of particles with size less than 10 μm (PM10) and flow velocities are measured synchronously at different heights in a sand storm, a high-Reynolds number multi-phase turbulent boundary layer. It is revealed that the low-speed very large scale motions (VLSMs) are recurrent with a frequency dominating the streamwise velocity power spectra and modulate the streamwise distribution of PM10 concentration. In the logarithmic layer, the low-speed VLSMs correspond to weak shear stress on the bottom surface and hence decrease the PM10 upward flux. In the higher region, the high-speed VLSMs enhance both the streamwise and the upward transportation of PM10 because of the positive correlation between the velocity and the particle concentration perturbations.

Synchronous multipoint measurements were performed in the atmospheric surface layer at the Qingtu Lake Observation Array site to obtain high-Reynolds-number $[{\mathrm{Re}}_{\tau }\sim O\left({10}^6\right)]$ data. Based on the selected high-quality data in the near-neutral surface layer, the spatial length scales of the large-scale dominant structures in the outer region of the turbulent boundary layer are investigated. The characteristic length scales are extracted from the two-point streamwise velocity correlations. Results show that the spatial length scales are invariant over a three order of magnitude change in Reynolds number $[{\mathrm{Re}}_{\tau }\sim O\left({10}^3\right)-O\left({10}^6\right)]$. However, they increase significantly with the wall-normal distance, showing reasonable collapses on outer-scaled axes. The variation of the spanwise width scale in the logarithmic region follows a linear increase, with the rate of increase much larger than that in the wake region. Moreover, the variation of the wall-normal length scale is also revealed, which displays a qualitative behavior similar to that of the spanwise width scale. The universal laws revealed in the present work contribute to a better understanding of the dominant structures in the outer region of the turbulent boundary layer at high Reynolds numbers.