This study employed the Weather Research and Forecasting (WRF) model to analyze variations in the PBL structures over a subtropical region (Hong Kong) and a mid-high latitude region (southeast England), predicted by different PBL schemes over a range of stability conditions. Evaluated were two nonlocal mixing PBL schemes, YSU and ACM2, and three local mixing PBL schemes, MYJ, Boulac and MYNN2. The PBL height predictions exhibit large intrascheme variance ( 20%). ACM2 diagnoses the PBL height thermodynamically using the bulk Richardson number method, which leads to a good agreement with the lidar data. The modeled vertical profiles, such as wind speed, exhibit large spreads across the PBL schemes. The turbulent kinetic energy (TKE) predicted by MYJ were found to be too small and...[ Read more ]

This study employed the Weather Research and Forecasting (WRF) model to analyze variations in the PBL structures over a subtropical region (Hong Kong) and a mid-high latitude region (southeast England), predicted by different PBL schemes over a range of stability conditions. Evaluated were two nonlocal mixing PBL schemes, YSU and ACM2, and three local mixing PBL schemes, MYJ, Boulac and MYNN2. The PBL height predictions exhibit large intrascheme variance (> 20%). ACM2 diagnoses the PBL height thermodynamically using the bulk Richardson number method, which leads to a good agreement with the lidar data. The modeled vertical profiles, such as wind speed, exhibit large spreads across the PBL schemes. The turbulent kinetic energy (TKE) predicted by MYJ were found to be too small and show much less diurnal variation as compared with observations over London. MYNN2 produces better TKE predictions at low levels (0-200 m AGL) than MYJ, but its turbulent length scale increases with height in the upper part of the strongly convective PBL. The local PBL schemes considerably underestimate the entrainment heat fluxes for convective cases.

This study also compares the predictions for momentum mixing from two nonlocal closure PBL models, i.e., the YSU and the modified Frech and Mahrt (FMX) PBL models, and from one local closure PBL model (YSU-local), using the WRF model. The YSU model, in which the nonlocal momentum flux is aligned with the surface wind shear, often predicts larger vertical wind shear than YSU-local in the interior of the convective PBL. In contrast, the FMX model produces more well-mixed wind profiles that agree better with observations and LES results than the YSU and YSU-local models, especially when the sign of the bulk wind shear in the convective PBL is opposite to that of the surface wind shear.