Team investigates freak winds
By Alison Ayres
UK engineers are employing wind tunnel experiments to study a destructive wind known as a thunderstorm downburst.
The wind occurs when a pocket of cold air up to two kilometres across falls rapidly to the ground during a storm.
As it falls, it curls in on itself like a mushroom cloud in reverse, sending air at hurricane speeds in all directions, with destructive force.
University of Surrey researchers hope their work will help improve aircraft safety and open structures like pylons.
Aviation danger
The man running the experiments in the wind tunnel at the Silsoe Research Institute (SRI) in Bedfordshire is Adam Robertson.
"Unlike tornadoes, downbursts are difficult to spot in the real world because they only last a few minutes. Very few have actually been witnessed," he told BBC Radio 4's Leading Edge programme.
One famous downburst was recorded in 1983 - and it nearly changed the course of history.
At Andrews Air Force base in Washington DC, US, instruments recorded a 150-mph (240 km/h) gust of wind - enough to cause a crash-landing.
Engineering cost
Only minutes earlier, Air Force One had landed carrying the then president of the US, Ronald Reagan.
More recently a Canadian downburst focussed minds even more sharply when it brought down an electricity pylon, resulting in a widespread blackout.
Gerry Parke is professor of civil engineering at Surrey University and believes that, ultimately, designing a structure to withstand these powerful and dynamic winds may prove too costly.
He says: "At the end of the day you might have to put so much steel into a pylon that it would be unacceptable visually".
The UK research contributes to a worldwide effort to tackle unanswered questions about the causes and impact of these winds.
Thunderstorm downbursts are known to occur in North America, Australia and South Africa, but may also threaten the UK.
Adam Robertson admits they are still something of a mystery. He says: "They are associated with thunderstorms. That's about the only thing we can be sure about. That's how they get their name."
http://news.bbc.co.uk/1/hi/sci/tech/3396173.stm
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