Interactions of charged dust with fog and clouds

Dust readily becomes highly electrified in many situations. This can lead to changes in its transport and properties, the initiation of discharges and ignition hazards. There are many interdisciplinary examples and applications of this, e.g. – Martian dust devils are thought to be electrified – and the handling of industrial powders, as grain silos, flour mills and mines have been demolished by electrostatic explosions. In military desert operations, charged dust can even generate visible discharges (St Elmo’s fire) around complex objects such as army helicopters, revealing them as targets to hostile forces.

The physical behaviour of dust in the atmosphere can be substantially changed when the dust becomes electrified, which often occurs very easily through natural motion and particle-particle interactions. For example, charged dust is preferentially removed over uncharged dust by water droplets, small dust particles have their fall speeds modified by electric forces and electrical alignment of dust aggregates has been suggested to explain the poor radiative representation of dust in models, which assume random orientations. Despite the expectation that electrification plays in these processes, research has been hampered by a lack of detailed observations and limited representation of the physical mechanisms. This project will utilize newly-developed instrumentation to provide pioneering new measurements of dust electrification, for use in constraining parameterizations of dust transport and removal. It will focus on investigating electrified dust interactions with cloud, as part of a major project in the Middle East to investigate the broader role of charge in cloud processes and rain generation.

Water clouds in the United Arab Emirates, where this work is being done, have been shown to have stable droplet size distributions, in which small droplets rarely grow into drops able to fall as rain. One explanation for this is the abundance of lofted dust which becomes entrained into clouds. Constraining the cloud water to small droplets is influenced by the collision efficiency between dust particles and cloud droplets, which is strongly affected by charge.

This project will characterize the electrification associated with dust transported into clouds, by a combination of direct measurements at the surface, remote sensing methods from the surface, and in-situ measurements using balloon and UAV (Unmanned Aerial Vehicle) platforms. The measurements will feed directly into modelling studies already underway in another strand of the international project, which are representing the turbulent mixing processes of charged droplets within clouds in unprecedented detail.

To provide more detail on the origins of the measured dust, the student will also utilize the Met Office dispersion model, NAME, to simulate case-studies of dust events. Comparison with the measurements will allow the evaluation of the modelled dust properties, as well as investigation into the source of the dust, and its subsequent transport. The combination of new physical understanding from the dust electrification measurements, and use of the NAME model, will ultimately allow the first implementation and testing of a charge parameterisation scheme. This is of great interest to the international dust modelling community and will provide new insight into dust transport processes.

TRAINING:
This predominantly experimental project will provide training and experience in instrumentation and fieldwork, and the analysis of data which can inform improvements in numerical models. Through the field work deployment in the Middle east, the student will interact closely with researchers from the Emirates, providing them first-hand experience of working in an international setting at an early stage in their career. Training in instrument science will occur through the courses at Reading in Measurements and Instruments (MSc), and Advanced Measurements (BSc). Further fundamental training key to the project will occur through the Atmospheric Chemistry and Transport module, Atmospheric Electricity module, and the Atmospheric Physics and Dynamical Meteorological provision. The student will also be strongly encouraged to attend the NERC short course on Practical use of unmanned aerial vehicles for atmospheric sciences, which Dr Nicoll (lead supervisor) co-organises.

To hear more about this project please follow the link: https://www.youtube.com/watch?v=o-yCyjra5dk&list=PLZWYaq_mWwsEM5dH1abHjYIgU2EVaegT9&index=4

To read more about this project please follow the link: http://www.met.reading.ac.uk/nercdtp/home/available/desc/entry2018/SC201832.pdf