An Improved Non‐Local Planetary Boundary Layer Parameterization Scheme in Weather Forecasting and Research Model Based on a 1.5‐Order Turbulence Closure Model.

Planetary boundary layer (PBL) modeling is a primary contributor to uncertainties in a numerical weather prediction (NWP) model due to difficulties in modeling the turbulent transport of surface fluxes. The Weather Research and Forecasting model (WRF) has provided many PBL schemes that may feature a non‐local transport component driven by large eddies or a one‐and‐half order turbulence closure model, but few of them possess the two features at once. In the present study, a turbulent kinetic energy (TKE)‐based eddy diffusivity/viscosity method is integrated into the non‐local Asymmetric Convective Model version 2 (ACM2) PBL scheme and implemented in WRF. The original first‐order eddy‐diffusivity term in ACM2 is discarded and an extra prognostic equation for TKE, which considers the tendency of TKE by buoyancy, wind shear, vertical transport, and dissipative processes, is supplied to calculate the diffusivity/viscosity. Non‐local transport is modeled the same as ACM2 using the transilient matrix method. Idealized tests using prescribed surface heat flux and roughness length are performed. TKE‐ACM2 displays advantages over the PBL scheme developed by Bougeault and Lacarrère (hereinafter referred to as Boulac) and ACM2 in the wind speeds (WS) profile because it better matches large‐eddy simulations results in the surface momentum flux. Real case simulations show that TKE‐ACM2 generally outperforms in the diurnal vertical profiles of WS under stable conditions. TKE‐ACM2 also produces a better alignment under moderately unstable conditions in the early nighttime at the urban LiDAR station. However, the model exhibits discrepancies more apparently under a more unstable condition during the winter daytime. Plain Language Summary: Large uncertainties in a numerical weather prediction (NWP) model arise from difficulties in accurately modeling the planetary boundary layer because of the chaotic motions of air. An adequate representation of vertical turbulent mixing processes in an NWP model usually requires the consideration of turbulent transport due to large‐scale buoyant plumes and a realistic while efficient turbulence closure model. The widely used NWP model, the Weather Research and Forecasting model, offers several algorithms to represent the turbulent transport of scalars and momentum in the PBL, but further developments are needed for particular schemes due to their drawbacks. Furthermore, little investigation has been done to assess the simulated vertical structures of wind speeds mainly constrained by the lack of high spatiotemporal resolution Doppler wind LiDAR data. In this research, we derived a new algorithm for modeling the vertical turbulent mixing processes that is based on the turbulent kinetic energy turbulence closure model. Simulations using idealized and real atmospheric conditions are performed to examine the performance of the new PBL scheme. Key Points: A new non‐local planetary boundary scheme, turbulent kinetic energy (TKE)‐Asymmetric Convective Model version 2 (ACM2), based on the TKE is proposed and evaluated with large‐eddy simulations (LES) and observationsIdealized simulations are conducted for TKE‐ACM2 to examine its sensitivity to key parameters including the weighting factor between local and non‐local fluxes and turbulent Prandtl number. Furthermore, it is shown that TKE‐ACM2 aligns better with LES results than ACM2 and Boulac under a prescribed convective conditionHigh spatiotemporal resolution Doppler LiDAR observations are used to evaluate the performance of the new scheme over the summer and winter seasons in Hong Kong. TKE‐ACM2 shows improvements over ACM2, particularly under stable conditions. TKE‐ACM2 also predicts the surface wind speeds considerably more accurately than other schemes at the urban stations in the summer case simulation [ABSTRACT FROM AUTHOR]