Evaluation of WRF model PBL schemes in simulating temperature extremes over the Middle-East – North Africa (MENA) region

A correct representation of the planetary boundary layer (PBL) is critical to achieve realistic simulations, especially regarding surface variables for regional climate simulations. In this study we examine the sensitivity of the performance of the Weather Research and Forecast (WRF) model to the use of three widely used PBL schemes with emphasis on heat extremes. This study aims (i) to explore the differences among the WRF simulated air temperature and heat extremes resulting from the choice of PBL schemes, (ii) to investigate the physical causes of model biases via the analysis of different variables and, finally, (iii) to reveal the most suitable scheme for application in the Middle-East - North Africa (MENA) domain. The schemes under evaluation are the Mellor–Yamada–Janjic (MYJ), Yonsei University (YSU), and the asymmetric convective model, version 2 (ACM2). We performed 11-year (2000-2010) simulations over the MENA region at 24km resolution. The simulations have been compared with the ERA5 reanalyses for several variables, including maximum and minimum 2-meter air temperature and indices of extremes. Results indicate that model biases strongly vary according to geographic area, with simulations showing good performance in some regions and substantial biases in others. Analysis of different variables like PBL height, moisture and heat fluxes show that differences among the schemes can be linked to differences in vertical mixing strength and entrainment of air from above the PBL.