Abstract/Summary

Measurements of atmospheric electrical variables in arid desert environments provide a route to assessing dust charging, which affects dust lofting; satellite remote sensing of dust particles; long range transport of elevated dust layers; and may also influence rain droplet size. This paper analyses a new dataset of atmospheric electric field (or Potential Gradient, PG) measurements from an arid site, at Al Ain in the United Arab Emirates (UAE), to investigate the influence of local meteorological and dust processes on the PG, and assess whether global atmospheric electric signals are detectable. With no data selection applied, the diurnal PG variation has a single maximum around 14UT (18LT), which is likely to be associated with the sea breeze, present on 77% of days in the central UAE. Despite the abundance of apparently fine days meteorologically, conventional atmospheric electricity fair weather selection criteria are not effective at removing all locally generated PG variability. Even applying much stricter selection criteria (10m wind speed U10 between 1 and 5m/s, visual range >25km, and no present weather), a diurnal variation in PG with a single maximum at 07UT (11LT) remains, likely due to local convection at sunrise. Although the stricter criteria can remove the sea breeze effect – associated with a visual range change - the PG measurements remain dominated by local meteorological and dust processes. This obscures the usual behaviour of the Global Electric Circuit. Exceptionally large PG values (~kV/m, even for U10<8m/s when no dust events are detectable visually) indicate that such desert regions can be a highly electrified environment, at least during daytime and during the summer convective months. The regular generation of highly charged dust observed is relevant to evaluating charge effects on large range transport of dust, preferential scavenging of charged dust by water droplets and obtaining accurate satellite retrievals of dust concentration.