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Last Updated: Friday, 11 July, 2003, 16:17 GMT 17:17 UK
UK, Holland top twister league
By Paul Rincon
BBC Science

Britain has the highest frequency of tornadoes, or twisters, over its land surface of any country in Europe, a report confirms.

Tornado
British tornadoes rarely cause much damage
The figures also show that the number of tornadoes in Europe each year could be around seven times greater than previously thought.

The UK experiences an estimated 50 tornadoes on land each year, putting it top of the European twister league. The Netherlands is in second place, with an estimated 35 twisters each year over its comparatively small land area.

Twisters are usually associated with the American Midwest, particularly the states of Oklahoma, Kansas and Nebraska - which comprise an area nicknamed "Tornado Alley".

An average 1,170 twisters are observed on land each year in the US. The most violent can cause widespread destruction to property and lead to many fatalities.

Under-reporting

The average number of tornadoes reported each year in the UK is actually 33. But the figure of 50 tornadoes per year takes into account under-reporting.

The report's author, Dr Nikolai Dotzek, of the German Aerospace Center in Wessling, Germany, was sceptical that this high figure is due to the UK having a radically different climatology to other maritime regions.

UK TORNADO FACTS
UK twisters, BBC
Most UK tornadoes are light or moderate in strength
Average number reported each year is 33 twisters
The maritime location may influence frequency
He explained that Britain's long history of tornado reporting could partially account for the high frequency in the UK.

This view is disputed, however - notably by Torro, the UK tornado and storm research group. It says the UK's higher latitude makes the country prone to depressions, where advancing cold fronts undercut hot air currents, creating good conditions for tornado formation.

Torro contributed data to the new report. The group has previously claimed that when land area is taken into account, the UK has the highest frequency of reported tornadoes per unit area in the world.

But according to the latest figures from 28 European countries, the Netherlands now takes that accolade.

Frontal collisions

Dr Terence Meaden, the founder of Torro, said that the areas of the UK most prone to tornadoes are the south and east of England.

"The highest might well be the south coast, east of the Isle of Wight," Dr Meaden told BBC News Online.

Tornadoes are spawned where hot and cold air streams collide. This creates a vortex, a fast-spinning funnel of wind, at the boundary where these two "fronts" meet.

But according to Dr Dotzek, British tornadoes are not generally as powerful as those in the US. Tornado intensity is often measured with the Fujita scale, which ranges from F0 (weak) to F5 (violent).

"Almost all tornadoes in the UK are weak. There are no F4 or F5 reports, just a very few F3s," said Dr Dotzek.

On average, 330 tornadoes are reported each year in Europe. The estimated "true" number of tornadoes is around 700 per year. In addition to tornadoes reported on land, this figure includes twisters observed on water, often referred to as waterspouts.

Until recently, many climatologists quoted a figure of around 100 tornadoes per year for Europe. This was based on an estimate made by the German scientist Alfred Wegener in 1917. It stuck for over eight decades.

The research is published in the journal Atmospheric Research.


SEE ALSO:
'Tornado' rips through houses
27 Oct 02  |  England
Storms cause 'mini tornado'
15 Oct 02  |  England


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