Abstract/Summary

Distinct differences in electrical characteristics of the atmosphere are observed during clear and foggy laden air. The presence of droplets in the air causes the removal of natural cluster ions and hence, a change in the electrical properties, which is useful for fog detection, and potentially fog forecasting. In this study, we report on some of the first electrical measurements conducted during fog in the United Arab Emirates (UAE). The analysis indicates that the Potential Gradient (PG) values observed during fog in the UAE were substantially higher than those previously reported in the literature (ranging from −1247 V/m to 1400 V/m). Furthermore, the PG during fog was often negative, with 93% of cases recording negative PG values (with median PG value of −397 V/m), particularly during wintertime fog events. A comparison with fog measurements conducted in the UK showed a stark contrast in PG behaviour between the two sites, with only positive PG values reported during fog in the UK (as is the case for the majority of PG fog studies reported in the literature), and higher PG variability in the UAE fogs. It is hypothesized that the unusual polarity of PG observed in UAE fog events may be attributed to the deposition of fog droplets, during which positive charges are transported from the top of the fog layer downwards towards the surface, thereby modifying PG. This deposition process is expected to be particularly active during the latter stages of the fog, when the droplet size distribution has fully evolved.