The characteristics of the atmospheric boundary layer turbulence over the Tibetan Plateau based on the ground-based C-band vertical radar

Based on observations of C-band frequency modulated continuous wave radar (BLH_Z), L-band radiosonde data (BLH_SD), gradient tower data and reanalysis data set (BLH_ERA5) at Naqu station in July and August 2014, the boundary layer height (BLH), turbulent statistical characteristics and turbulent spectrum in surface layer and mixing layer under different sensible heat fluxes (SH) and stability (z/L or BLH_Z/L) conditions are analyzed. The main results are as follows: (1) There are significant correlation among BLH_Z , BLH_SD and BLH_ERA5, and the root mean square deviations among them are about 0.6 km. The BLH_Z have significant daytime variation at Naqu, and the daily range of the median of BLH_Z is approximately 0.7—0.8 km. At around 16:00 BT, BLH_Z reaches its maximum value with a median value of approximately 1.2 km. (2) All of \sigma _\mathrmw,\sigma _\mathrmT and R_wT in surface layer gradually increase with increased SH. The \sigma _\mathrmT generally increases linearly, and the increase rates of \sigma _\mathrmw and R_wT gradually decrease when SH exceeds a certain threshold. When −z/L＜0.3, both \sigma _\mathrmT and R_wT rapidly increase with the increase of −z/L; when −z/L≥0.3, the increase rate significantly decline. (3) The maximum value of \sigma _\mathrmw^2 in mixing layer occurs at a height of approximately (0.25—0.3)×BLH_Z, with an average value of approximately 1.2—1.3 m²/s². The \sigma _\mathrmw^2 in mixing layer under strongly unstable stratification is slightly less than that under weakly unstable stratification; the average value of \sigma _\mathrmw^2 in mixing layer increases with the increasing of SH. With the increase of z/BLH_Z, \sigma _\mathrmw^2 / w_*^2 presents a first rapid increase and then gradually decreases, with the maximum value occurring at around 0.35×BLH_Z. (4) With the increase of unstable stratification, the peak frequency of the normalized vertical velocity spectrum both in surface layer and mixing layer moves towards low frequency and its corresponding value (normalized power spectral density) increase. Both the scale of the turbulent vortex and turbulent intensity increase for strongly unstable stratification.