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 plays a critical role in a numerical weather forecasting model. 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 the numerical method to couple one of the recently validated PBL schemes, TKE-ACM2, with the multi-layer Building Effect Parameterization (BEP) model in WRF. Subsequently, the performance of TKE-ACM2+BEP has been examined under idealized convective atmospheric conditions with a simplified building layout. Furthermore, its reproducibility is benchmarked with one of the state-of-the-art large-eddy simulation models, PALM, which can explicitly resolve the building aerodynamics. The result indicates that TKE-ACM2+BEP outperforms the other operational PBL scheme (Boulac) coupled with BEP by reducing the bias in both the potential temperature (θ) and wind speed (u). Following this, real case simulations are conducted for a highly urbanized domain, i.e., the Pearl River Delta (PRD) region in China. The high-resolution wind speed LiDAR observations suggest that TKE-ACM2+BEP can mitigate the overestimation in the lower part of the boundary layer compared to the Bulk method at a LiDAR site located in a densely built environment. In addition, the surface temperature and relative humidity can be improved in TKE-ACM2+BEP at surface stations in urbanized areas compared to TKE-ACM2 without BEP. However, it is revealed that BEP may not always imply a better reproduction of surface wind speed as it could exert excessive aerodynamic drag.