What's in a name?

7.08.08 16:13

There is a reluctance sometimes to call a spade a spade; or in this instance, and in this country, a tornado a tornado.

Far more popular is the epithet “mini-tornado”, whatever damage might accrue. It is almost as if the full-blown phenomenon should be thought an impossibility in our relatively benign and temperate climate. 

Across the Channel, the same prejudice is evident: when a twister struck the town of Hautmont in northern France last week and killed three people on its destructive rampage, it was widely reported as “une mini-tornade”.

A tornado is a tornado, however, whatever its size, just as long as it conforms to certain criteria. The American National Weather Service and the American Meteorological Society both define a tornado, very briefly, as “a violently rotating column of air” that extends from the base of a convective cloud to the ground, and call it “the most destructive of all local-scale atmospheric phenomena”.

Tornadoes are associated with torrential downpours, thunderstorms and hail. Such storms often produce strong gusts and squalls, of course, but “violently rotating” is the distinguishing feature. It is unlikely that even a strong squall could move or lift cars and tear apart houses as the Haumont tornado did.

So why the coyness? Perhaps because it is true to say that here in Europe we do not experience the hugely destructive monsters so prevalent in the USA, notwithstanding last week’s events in northern France, or even the tornadoes in Birmingham in 2005 and north London in 2006.

When compared, for example, with the devastation wrought by a huge outbreak of tornadoes in Kansas during May last year, it is perhaps understandable - if technically incorrect - that we qualify the term. A massive tornado flattened virtually the entire city of Greensburg: it was 1.7 miles across, travelled for 22 miles and brought almost unimaginable winds, peaking at an estimated 205mph. This rated it EF5 on the Fujita scale of tornado strength, the highest category.

Such wholesale devastation has, thankfully, been rare in the US this year, but 2008 is, nevertheless, shaping up to be one of the most active years for tornados in history.

The record is held by 2004, when 1,717 tornadoes touched down across the USA through the year. So far this year, nearly 1,600 have been reported, which already puts 2008 second on the all time list.

Conceivably the 2004 mark could be surpassed, but tornadoes are becoming less frequent, as they are wont to do at this time of year; the peak is spring and early summer. Another factor in the waning frequency is, perhaps, the weakening of the latest La Niña episode.

La Niña, in a nutshell, is the anomalous cooling of the eastern and central equatorial Pacific. El Niño, in passing, is just the opposite. Both phenomena have far-reaching meteorological consequences, although some connections are weaker than others.

There is a strong body of evidence that La Niña causes, for example, drought in the south-western States but an increase in tornadic activity further east, which would certainly help to explain such a lively year.

As far as Europe and the British isles are concerned, such correlations are weaker, although some scientists propose that La Niña brings a wetter summer. If so, then we should not be surprised by the recent rain, nor the rain that is still to come.

By: Stephen Davenport