Desert dust puzzle solved

(PhysOrg.com) -- Pioneering measurements by University of Reading scientists are helping to unravel a mystery over strange properties of atmospheric dust.

Why some airborne dust particles clump together to let energy through like a ‘venetian blind' has been a puzzle, which the Reading researchers set out to explain using a balloon measurement campaign off west Africa.

Working with collaborators from the University of Hertfordshire, the Reading researchers found that the dust blown hundreds of miles from the Sahara desert carried electric charge, which provides a possible explanation for the clumping phenomenon.

Dr. Keri Nicoll, from the Department of Meteorology at Reading, led the expedition to the Cape Verde Islands, which experience frequent Saharan dust clouds, to measure the electrical properties of the particles high in the atmosphere above. While dust charges have been measured in the atmosphere near the Earth's surface, there is little direct information on dust aloft.

A weather balloon sounding system, designed by Reading's Professor Giles Harrison and Dr. Nicoll, measured dust clouds up to 4km in altitude and found that charge was present inside the dust clouds. Dust charging affects the behaviour of dust, such as the removal of dust by cloud droplets, particularly for small particles. Sometimes Saharan dust is even found as far afield as the southern UK, washed out by rain.

Dr. Nicoll said: "Whilst it is known that dust can charge near the ground, these measurements of charged dust well above the surface are unusual and may even be the first of their kind."

Professor Harrison said "An accurate knowledge of dust's properties is important to characterise it properly for climate simulations. There is a broader relevance of this understanding too as charging is also suspected to affect dust elsewhere in the solar system, such as on Mars. "