Evaluation of three planetary boundary layer schemes in the WRF Model

Accurate depiction of meteorology, especially in the planetary boundary layer (PBL), is important for air pollution modeling. The PBL parameterization schemes play a critical role in simulating the boundary layer meteorology. This study examines the sensitivity of the performance of the Weather Research and Forecast (WRF) model to the use of three different PBL schemes (MYJ, YSU, and ACM2). Comparison of 92 sets of daily, 36-hr cloud-resolving WRF simulations with different schemes over Texas in July-September 2005 shows that both the YSU and ACM2 schemes give significantly less bias than the MYJ scheme. The MYJ scheme, the only local closure scheme of the three, predicted systematically the coldest and moistest biases in the PBL, apparently due to weaker vertical mixing and underestimated entrainment processes. The importance of vertical mixing is investigated in experiments with the WRF model with altered vertical mixing strength. Similar PBL scheme differences appear to account for the difference in model performance found in other similar WRF applications. This study also provides guidance for future high-resolution modeling of air-pollution meteorology and facilitates future improvements in the PBL schemes.