Published 12 August 2020 • © 2020 The Author(s). Published by IOP Publishing Ltd
https://iopscience.iop.org/article/10.1088/1748-9326/ab9e20
Environmental Research Letters
LETTER • THE FOLLOWING ARTICLE ISOPEN ACCESS
Consistent dust electrification from Arabian Gulf sea breezes
Keri Nicoll1,2, Giles Harrison1, Graeme Marlton1 and Martin Airey1
Abstract
The Arabian Gulf region experiences regular thermally driven sea breeze circulations which occur all year round, penetrating hundreds of kilometres inland.
As a sea breeze front moves inland, substantial electric fields are generated by separation of charged desert dust.
In the first surface electric field measurements made in the United Arab Emirates (UAE), consistent and repeatable substantial electric field changes with magnitudes up to 7 kV m−1 have been detected at Al Ain (170 km from the western coast), during 80 separate sea breeze events in 2018. Every sea breeze frontal passage shows the same characteristic signature of a transient maximum peak in electric field lasting tens of minutes. Electric field changes during these events were always negative (i.e. enhancing the existing negative 'fair weather' electric field), in contrast to many other reported observations in dust storms in which conditions were less repeatable.
The regular and substantial dust electrification found demonstrates that accurate representation of dust in climate and weather models requires electrical effects to be addressed, both in the generation process, and by considering aggregates in radiative transfer calculations as electrically aligned rather than randomly ordered.
Furthermore, satellite aerosol retrievals are affected by the changed attenuation of electromagnetic radiation when dust particles are charged, for which corrections may be needed.
1. Introduction
Electrification of dust in the atmosphere occurs readily, with its effects made apparent in sparks from barbed wire fences during the 1930s 'Dust Bowl' in the US [1], and helicopter blades glowing from corona discharge in dusty environments [2].
Dust electrification can result from contact charging/triboelectrification [3, 4], during dust generation or its atmospheric transport [5, 6]. Charging of dust particles, and separation of the charge by mechanical processes yields large electric fields (E-fields), which can be several orders of magnitude larger (up to tens of kV m−1) than those more typical of fair weather conditions in non-desert regions.
These fields are substantial enough to alter the properties of insulators on transmission lines in desert areas, reducing the flashover voltage [7].
Dust electrification also has applications to climate studies, through electrical influences on the behaviour of dust, and its radiative behaviour in particular [8].
Satellite remote sensing of dust is based on measurements of electromagnetic wave propagation which are attenuated by large electric fields [9], thereby the accuracy of dust measurements can be affected by electric fields arising from charge separation in dusty environments. Large E-fields associated with charge separation in dust layers are also expected to alter the orientation of dust particles, changing the effective optical depth of dust layers [10], existing calculations for which assume randomly oriented particles.
Further consequences associated with dust electrification are that the dust lofting process itself can be altered when the E-field intensity exceeds a threshold value (thought theoretically to be 150 kV m−1 in the few cm closest to the surface) [11]. This results in a sudden increase in the concentration of lofted particles at a given wind speed [12], unaccounted for in dust source modelling.
Finally, electrification of dust particles has also been suggested to alter the transport of the dust particles by increasing the time spent aloft through interaction with the background E-field [5, 8]. Due to the developing knowledge concerning dust charging processes in the real atmosphere, no attempts have yet been made to incorporate the role of dust charging into satellite retrievals of dust, or in modelling the dust source regions which are key to accurate predictions from weather and global climate models.
Study continues at: https://iopscience.iop.org/article/10.1088/1748-9326/ab9e20
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