The First Characterization of Fog Microphysics in the United Arab Emirates, an Arid Region on the Arabian Peninsula

Abstract

AbstractFog microphysics characteristics play an important role in fog life cycle, radiation and visibility. Measurements of fog microphysics are important in understanding these processes and improving existing model parameterization schemes. From 28 January to 17 February 2021, we carried out the first measurements of fog microphysics in the arid region of the United Arab Emirates and present initial results in this paper. Five events occurred, the longest lasting about 4 hr 28 min and the remaining lasting 2 hr or less. In this study, the meteorological conditions at synoptic scale associated with the formation of fog, are presented as well as the microphysics characteristics of fog. Maximum cloud droplet count ranged from 80 to 700 cc, Liquid Water Content (LWC) from 0.06 to 0.58 g m−3 and the Median Volume Diameter reached 25 μm in all the cases. The estimated Liquid Water Path reached a maximum of 100 g m−2. The size distribution was bimodal for all visibility classes of mist, fog and thick fog with modes at around 4.5 μm and between 22 and 25 μm. The droplet size distribution broadened as the mature phase progressed, demonstrating a decrease in droplets in the 6–16 μm range and an increase in droplets above 19 μm. During the mature stage, droplet growth was observed with no associated decrease in LWC, suggesting growth by collision and coalescence was occurring. However, LWC did increase concurrently suggesting droplet growth by condensation was also taking place.