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WRF Ensemble Simulations Help Researchers Predict Optimal Conditions for Summer Time Precipitation Events Over UAE’s Eastern Region

The climate of the UAE, much like the rest of the Arabian Peninsula, is characterized by high temperatures and low precipitation amounts. These conditions result in annual precipitation amounts between 20 and 130 mm from west to east, which are produced mainly during the winter–spring period, whereas the summer time precipitation is only around 20% of the annual precipitation.

Despite the low amount of natural summer time rainfall over UAE, favorable conditions for rain enhancement through cloud seeding can still exist. This led Prof. Volker Wulfmeyer, a First Cycle Awardee of UAE Research Program for Rain Enhancement Science (UAEREP) and Managing Director and Chair of Physics and Meteorology at the Institute of Physics and Meteorology of the University of Hohenheim in Stuttgart and his team to study a typical precipitation event occurring during summer time over the eastern part of the country. The understanding and correct simulation of these effects is crucial for the prediction of extreme events and for the application of weather modification efforts like cloud seeding and rain enhancement.

Prof. Volker and his team used a five‐member Weather Research and Forecasting (WRF) physics ensemble on the convection‐permitting (CP) scale and investigated its ability to simulate convection and precipitation by varying the applied cloud microphysics and planetary boundary layer (PBL) parametrizations.

The results of this study showed that the application of water‐ and ice‐friendly aerosols in combination with an aerosol‐aware cloud microphysics and the Mellor‐Yamada‐Nakanishi‐Niino (MYNN) PBL parametrization is the most suitable combination to simulate convection over the UAE. It also found that even a small physics ensemble is able to simulate the pre-convective and convective environment reasonably. This will help increase the reliability of potential cloud‐seeding applications over the UAE.

The study investigated the potential of the WRF model to resolve a convective event during July, 2015 over the UAE. Future work will include a refinement of the ensemble design by adding more members, by not only changing the applied physics scheme but also varying parameters such as surface roughness length, aerosol concentrations, and mixing length‐scales. To enhance the process, more summer time case studies and the application of variational data assimilation procedures have to be considered. This will help further enhance our understanding of the predictability of clouds and precipitation for cloud‐seeding applications.

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