WRF Gray‐Zone Simulations of Precipitation Over the Middle‐East and the UAE: Impacts of Physical Parameterizations and Resolution

Abstract

AbstractSeveral single‐year‐long (2017) simulations with different configurations of the Weather Research and Forecasting (WRF) model over the United Arab Emirates (UAE) and the Middle‐East at the convective gray‐zone resolution (9 km) are evaluated in their ability to capture the temporal and spatial distributions of precipitation. Annual rainfall over the Middle‐East is dominated by wintertime precipitation and is mostly initiated by the frontal systems intrusion. WRF at 9 km resolution shows good skill in capturing the synoptic and meso‐scale precipitation distributions. The aerosol‐aware Thompson microphysics scheme outperforms the WRF double moment 6 class microphysics by about 20% in annual mean precipitation over the Middle‐East. Different Planetary Boundary Layer (PBL) physics leads to large differences in the annual rainfall over both the Middle‐East (about 30%) and the UAE (about 45%). The Quasi‐Normal Scale Elimination (QNSE) PBL scheme produces stronger precipitation than the Asymmetrical Convective Model and is in better agreement with observations. This difference is attributed to the former scheme producing a warmer and moister lower‐level atmosphere that builds more substantial instability. Regions of stronger instability also depict decreases in lifting condensation level heights and increases in boundary layer height, suggesting that the boundary layer reaching the cloud base helps to trigger the convection and increase precipitation. Refinement in grid spacing (5 km) marginally improves the summertime precipitation over the Middle‐East but significantly increases the computational cost. Current study also indicates that gray‐zone simulations can perform as good as convection‐permitting simulations by carefully choosing the right model physics packages for the synoptic and meso‐scale precipitation.