Added Value of Three‐Dimensional Planetary Boundary Layer Schemes for Simulating Local‐Scale Circulations Over Complex Terrain on the Tibetan Plateau

Abstract

Complex terrain and heterogeneous land surfaces on the Tibetan Plateau (TP) induce local‐scale circulations such as mountain‐valley winds and lake‐land breezes. Most numerical models employ one‐dimensional (1D) planetary boundary layer (PBL) schemes that inadequately represent horizontal turbulent mixing, resulting in poorly represented local‐scale circulations. In contrast, three‐dimensional (3D) PBL schemes account for turbulent mixing in both the vertical and horizontal directions. In this study, we assessed the performance of six PBL schemes, including 1D and 3D schemes, in the Weather Research and Forecasting (WRF) model for simulating local‐scale circulations validated against in situ observations. The results demonstrate that 3D PBL schemes outperform 1D PBL schemes in capturing key features of local‐scale circulations. The 3D PBL schemes accurately reproduce the intensity and duration of strong afternoon winds in the Mt. Qomolangma region, as well as the vertical structure and temporal evolution of lake breezes in the Nam Co region on the TP. In the Mt. In the Qomolangma region, the 3D schemes successfully simulate the observed southwesterly afternoon winds. They achieve this by incorporating a westerly momentum component from the western slopes into the local valley wind through horizontal turbulent mixing, a process absent in 1D schemes. However, a critical limitation of 3D schemes is their excessive horizontal diffusion under stable nighttime conditions in the Nam Co region, which smooths out thermal gradients and leads to a complete failure in capturing the land breeze's defining southerly flow with wind speed increasing with height. These findings highlight that while accounting for horizontal turbulent mixing through 3D PBL schemes is essential for daytime convective boundary‐layer circulations over complex terrain, its treatment requires careful consideration during stable conditions.