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

Abstract

We assess the sensitivity of the Weather Research and Forecast (WRF) model to the use of different planetary boundary layer (PBL) parameterizations focusing on air temperature and extreme heat conditions. This work aims to evaluate the performance of the WRF model in simulating temperatures across the Middle-East - North Africa (MENA) domain, explain the model biases resulting from the choice of different PBL schemes, and identify the best performing configuration for the MENA region. Three different PBL schemes are used to downscale the ECMWF ERA-Interim climate over the MENA region at a horizontal resolution of 24 km, for the period 2000–2010. These are the Mellor–Yamada–Janjic (MYJ), Yonsei University (YSU) and the Asymmetric Convective Model, version 2 (ACM2). For the evaluation of the WRF runs we used related meteorological variables from the ERA5 reanalysis including summer maximum and minimum 2-meter air temperature and heat extreme indices. Our results indicate that simulations tend to overestimate maximum and underestimate minimum temperatures, while we find that model errors are very dependent on the geographic location. The possible physical causes of model biases are investigated through the analysis of additional variables (such as boundary layer height, moisture and heat fluxes). It is shown that differences among the PBL schemes are associated with differences in vertical mixing strength which alters the magnitude of the entrainment of free-tropospheric air into the PBL. The YSU is found to be the best performing scheme and it is recommended in WRF climate simulations for the MENA region.