Elucidating the boundary-layer turbulence profiles observed by a radar wind profiler network in the Tibetan Plateau

The planetary boundary layer (PBL) over the Tibetan Plateau (TP) imposes significant impact on regional and global climate, while its vertical structures and evolution features remain poorly understood. This study examines the evolution and possible mechanisms of daytime PBL turbulence profiles for cloud- and clear-sky conditions by using one-year observations from the radar wind profiler (RWP) network deployed over the TP, in combination with the measurements from the automatic weather station (AWS), millimeter-wave cloud radar (MMCR). The results show that the turbulence dissipation rate (e) are stronger and PBL height is higher in the norther part of TP (NTP), compared with those in the southern part of TP (STP). The presence of clouds inhibits turbulence transport within the PBL over the NTP, while the opposite effect was found over STP. Analysis of surface-air temperature difference and wind shear data shows that both the thermal and dynamical effects strengthen the turbulence within PBL, and the thermodynamic effect is more important over STP than the NTP. The probability of PBL-cloud coupling is higher over the STP, and the cloud is found to enhance the PBL turbulence due to the strong wind shear, even although clouds can reduce the PBL height through radiative cooling effect. The findings help fill our knowledge gap in the PBL turbulence profiles throughout the whole TP, and highlight the significant role of the interaction between PBL turbulence and cloud in affecting the development of PBL turbulence over the whole TP.