Saharan dust plume charging observed over the UK

R Giles Harrison, Kerianne Nicoll, Graeme J. Marlton, Claire L. Ryder, A. J. Bennett

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Abstract

A plume of Saharan dust and Iberian smoke was carried across the southern UK on 16th October 2017, entrained into an Atlantic cyclone which had originated as Hurricane Ophelia. The dust plume aloft was widely noticed as it was sufficiently dense to redden the visual appearance of the sun. Time series of backscatter from ceilometers at Reading and Chilbolton show two plumes: one carried upwards to 2.5 km, and another below 800 m into the boundary layer, with a clear slot between. Steady descent of particles at about 50 cm s-1 continued throughout the morning, and coarse mode particles reached the surface. Plumes containing dust are frequently observed to be strongly charged, often through frictional effects. This plume passed over atmospheric electric field sensors at Bristol, Chilbolton and Reading. Consistent measurements at these three sites indicated negative plume charge. The lower edge plume charge density was (-8.0 ± 3.3) nC m-2, which is several times greater than that typical for stratiform water clouds, implying an active charge generation mechanism such as turbulent triboelectrification. A meteorological radiosonde measuring temperature and humidity was launched into the plume at 1412 UTC, specially instrumented with charge and turbulence sensors. This detected charge in the boundary layer and in the upper plume region, and strong turbulent mixing was observed throughout the atmosphere’s lowest 4 km. The clear slot region, through which particles sedimented, was anomalously dry compared with modelled values, yet water clouds were forming intermittently in the air beneath. We conclude that charging enhanced the particle hygroscopicity, drying the atmosphere and transporting water vapour into the cloud-forming region beneath. Inclusion of the electrical aspects in numerical models is required in order to accurately represent particle transport, and its effects in the atmosphere, particularly concerning cloud microphysical properties.

Original languageEnglish
Article number054018
Number of pages9
JournalEnvironmental Research Letters
Volume13
Issue number054018
DOIs
Publication statusPublished - 4 May 2018

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Dust
Atmosphere
Cyclonic Storms
plume
dust
Reading
Wettability
Boundary layers
Water
Steam
Solar System
Humidity
Radiosondes
Smoke
Hurricanes
Sensors
Charge density
cloud water
Air
Sun

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Harrison, R. G., Nicoll, K., Marlton, G. J., Ryder, C. L., & Bennett, A. J. (2018). Saharan dust plume charging observed over the UK. Environmental Research Letters , 13(054018), [054018]. https://doi.org/10.1088/1748-9326/aabcd9

Saharan dust plume charging observed over the UK. / Harrison, R Giles; Nicoll, Kerianne; Marlton, Graeme J.; Ryder, Claire L.; Bennett, A. J.

In: Environmental Research Letters , Vol. 13, No. 054018, 054018, 04.05.2018.

Research output: Contribution to journalArticle

Harrison, RG, Nicoll, K, Marlton, GJ, Ryder, CL & Bennett, AJ 2018, 'Saharan dust plume charging observed over the UK', Environmental Research Letters , vol. 13, no. 054018, 054018. https://doi.org/10.1088/1748-9326/aabcd9
Harrison, R Giles ; Nicoll, Kerianne ; Marlton, Graeme J. ; Ryder, Claire L. ; Bennett, A. J. / Saharan dust plume charging observed over the UK. In: Environmental Research Letters . 2018 ; Vol. 13, No. 054018.
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