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Think
of tornadoes and you probably think of the Great Plains of America
- the setting for films such as the Wizard of Oz and Twister. That
is certainly where the deadliest of them originate. (The Tristate
Twister of 1925 travelled over 200 miles, killing almost 200 people
and injuring another 2000.)
We
get more than our fair share of tornadoes in the West Country.
Nature loves a vortex. |
| Richard
Angwin |
Whilst
the United States are home to the biggest and most destructive tornadoes,
they have been recorded on every continent - even Antarctica - and
the UK has the highest reported frequency per unit area, in the
world.
We
get more than our fair share of tornadoes in the West Country. Nature
loves a vortex.
Remember
the Richardson quotation:
"Big
whirls have little whirls that feed upon their velocity,
And little whirls have lesser whirls, and so on, to viscosity."
Vortices
are easy to induce in a column of water, but given the right atmospheric
conditions - moist, rising air, instability aloft and a change of
wind direction with height, we can produce some twisters of our
own.
The
footage of a funnel cloud captured by Bill
 |
| Full
tornado status occurs when the funnel 'touches down' |
Shackleton
at Pylle in Somerset in August 2002 didn't quite make it to full
tornado status as it didn't touch down.
But
tornadoes have been reported around the Chew Valley and over Salisbury
Plain in particular.
Even
if they don't build from the cloud down, vortices can develop from
the ground up as the dust devils that can frequently be seen over
the farmland across the region testify.
The
biggest tornadoes can be killers. Fortunately fatalities in this
country are rare which is just as well because we are still a long
way from being able to predict when and where they will occur. But
with global warming they could well become a more common sight in
the West in future.
by
Richard Angwin
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