An Improved Non-local Planetary Boundary Layer Parameterization Scheme
in Weather Forecasting and Research Model Based on a 1.5-order
Turbulence Closure Model
Abstract
Planetary boundary layer (PBL) modeling is a primary contributor to
uncertainties in a numerical weather prediction model due to
difficulties in modeling the turbulent transport of surface fluxes. The
Weather Research and Forecasting model (WRF) has included many PBL
schemes which may feature a non-local transport component driven by
super-grid eddies or a one-and-half order turbulence closure model. In
the present study, a turbulent kinetic energy (TKE)-based turbulence
closure model is integrated into the non-local Asymmetric Convective
Model version 2 (ACM2) PBL scheme and implemented in WRF. Non-local
transport is modeled the same as ACM2 using the transilient matrix
method. The new TKE-ACM2 PBL scheme is evaluated by comparing it with
high spatiotemporal Doppler LiDAR observations in Hong Kong over 30 days
each for summer and winter seasons to examine its capability in
predicting the vertical structures of winds. Scatter plots of measured
versus simulated instantaneous wind speeds show that TKE-ACM2 is able to
reduce the root mean square error and mean bias and improve the index of
agreement, especially at the urban observational site. The diurnal
evolution of monthly averaged wind profiles suggests TKE-ACM2 can better
match both the magnitudes and vertical gradients, revealing its
superiority compared to ACM2 at stable atmospheric conditions. Other
meteorological parameters including the potential temperature profiles,
PBL heights, and surface wind speeds have also been investigated with
references to various sources of observations.