Coupling the TKE-ACM2 Planetary Boundary Layer Scheme with the Building Effect Parameterization Model

Abstract. Understanding and modeling the turbulent transport of surface layer fluxes are essential for numerical weather forecasting models. The presence of heterogeneous surface obstacles (buildings) that have dimensions comparable to the model vertical resolution requires further complexity and design in the planetary boundary layer (PBL) scheme. In this study, we develop a numerical method to couple a recently validated PBL scheme, TKE-ACM2, with multi-layer Building Effect Parameterization (BEP) in the Weather Research and Forecasting (WRF) model. Subsequently, the performance of TKE-ACM2+BEP is examined under idealized convective atmospheric conditions with a simplified building layout. Furthermore, its reproducibility is benchmarked with a state-of-the-art large-eddy simulation model, PALM, which explicitly resolves the building aerodynamics. The results indicate that TKE-ACM2+BEP outperforms another operational PBL scheme (Boulac) coupled with BEP by reducing bias in both the potential temperature (θ) and wind speed (u). Following this, real case simulations are conducted for a highly urbanized domain, namely the Pearl River Delta (PRD) region in China. High-resolution wind speed LiDAR observations suggest that TKE-ACM2+BEP reduces overestimation in the lower part of the boundary layer compared with the Bulk method, which lacks an urban scheme, at a LiDAR site located in a densely built environment. In addition, the surface temperature and relative humidity given by TKE-ACM2+BEP at surface stations in urbanized areas are more accurate than those given by TKE-ACM2 without BEP. However, it is revealed that BEP does not always improve the accuracy of the surface wind speed, as it can introduce excessive aerodynamic drag.