On the analysis of a summertime convective event in a hyperarid environment

A summertime convective event that developed on 5 September 2017 over the United Arab Emirates (UAE) is investigated in this study. Atmospheric profiles from a ground-based microwave radiometer along with satellite observations and in situ data from three weather stations in the UAE were used. The event was simulated using the Weather Research and Forecasting (WRF) model, forced with four input datasets: Global Forecast System (GFS), Climate Forecast System Reanalysis (CFSR), and the European Centre for Medium-Range Weather Forecasts ERA-5 and ERA-Interim reanalyses. The afternoon and evening convection was triggered by the intrusion of a mid-level trough from midlatitudes and was favoured by the convergence over land of thermally forced maritime air masses. Near-surface observations at a weather station revealed a 7 °C drop in air temperature, a doubling of the wind speed to 9 m·s⁻¹ in 30 min, and a shift in wind direction from easterly, to southerly and then westerly in about 45 min, associated with the passage of the cold pool emanating from a Mesoscale Convective System (MCS). At the location where the microwave radiometer was deployed, the pre-squall low and wake low signatures are also captured, with a 5 m·s⁻¹ increase in the wind speed in just 5 min. The observed features of the studied MCS were found to compare with those reported for MCSs in the Tropics. The four experiments gave a similar performance, although the GFS simulation generally generated higher skill scores. The investigated MCS event was not captured by WRF, which was attributed to a misrepresentation of soil moisture in the model. This study highlights the difficulties regional models like WRF may have in reproducing MCSs over arid/hyperarid regions, which may result in a misrepresentation of their impacts in climate projection studies.