On the investigation of the typology of fog events in an arid environment and the link with climate patterns

Abstract

The central aim of this work is to investigate the characteristics of fog events over the United Arab Emirates (UAE) and identify the underlying physical processes responsible for fog initiation and dissipation. To achieve this, hourly meteorological measurements at eight airport stations, along with ERA5 reanalysis data (1995- 2018), are utilized. The analysis indicates the dominance of radiation fog (RAD) as, on average, 70% of the observed events fall under this category. Fog in theUAE typically forms between 2000 and 0200 local time (LT) and dissipates between 0600 and 0900 LT. During a typical dense fog event recorded during 22-23 December 2017, cooling and moistening tendencies of up to 1.2Kh-1 and 0.7 g kg-1 h-1 are observed ;5-6 h before fog onset. In the vertical, a dry andwarmlayer above 750 hPa gradually descends fromabove 500 hPa to promote the development of fog. Similar conclusions are reached when analyzing composites of fog events. Further, the variability of fog occurrence associated with El Niño-Southern Oscillation (ENSO) patterns is explored. It is concluded that the El Niño (warm) and La Niña (cold) phases exhibit very different spatial characteristics with respect to surfacemeteorological variables. In particular, during El Niño events, the near-surface atmosphere is cooler andmoister compared to La Niña events, favoringRADfog formation over theUAE.Besides, fog events during El Niño years tend to last longer compared to La Niña years due to an earlier onset.