Narendra Nelli

Tropical cyclones (TC) are one of the biggest natural hazards with significant threat to life and property due to storm surge, flooding and extreme winds. Combined, these hazards substantially increase the potential for loss of life and damage especially in populated landfall‐locations such as the countries on the Arabian Gulf and Sea of Oman. Hence, it is important to identify the factors that modulate the trajectory of TC in order to better predict their lifetime and dynamics. Since 1900, only two TCs moved into the Sea of Oman and made landfall on the southeastern coast of the Arabian Peninsula (AP): TC Shaheen in 2021 and Gonu in 2007. In this study, the mechanisms behind the exceptional trajectories of these two TCs are investigated. Both TCs developed during the active phase of the Madden‐Julian Oscillation, and benefited from above‐average sea surface temperatures (SSTs), ocean heat content and reduced vertical wind shear. Their paths over the Indian Ocean were controlled by large‐scale forcings, whereas regional‐scale processes, such as the local SST gradients and the Arabian Heat Low (AHL) defined their trajectories near landfall location over the AP. An exceptionally deep AHL was present during these events. The AHL is found to interact two‐way with TCs: its associated circulation drags the TCs inland while the TCs, through the advection of cooler marine‐air inland, cause the collapse of the AHL. It is recommended to account for the AHL as fluctuations in its position and strength can determine where future TCs make landfall.

Fog 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.