Ten days ago, northsiders in Dublin received a nasty shock. At about 6 p.m. on August 17th, a tornado came ashore on Dollymount Strand and moved quickly northwards towards Raheny before disappearing as rapidly as it had formed.
No injuries or major damage were reported, but Dubliners, naturally enough, were worried lest this be a portent of worse things to come. A tornado blowing down a tree or two in Letterfrack, or turning over a haystack down in Clonakilty, is merely nature in the raw; when nature puts in an appearance in metropolitan suburbia, perhaps it's time to take this talk of climate change more seriously?
Because of their frequency and high profile in the US, we tend to think of tornadoes as American phenomena, but they can, and do, occur virtually anywhere in the world outside the polar regions. Every year, there are about 100 to 150 tornadoes in the south of England. Here in Ireland they are comparatively rare, with perhaps 10 or 20 being reported every year. Moreover, Irish tornadoes are considerably less vicious than their continental or transatlantic cousins, but they are full-blown tornadoes, none the less.
Although small-scale and very localised, being perhaps only 10 metres in diameter, a tornado is the most violent of all windstorms - a swirling maelstrom of air with a lifespan of anything from a few minutes to an hour. They form in thundery conditions when a body of anomalously warm, moist air near the ground causes the atmosphere to become what meteorologists call "unstable". This instability results in strong persistent updraughts in the atmosphere - fountains of air surging upwards which eventually produce thunderstorms, hail and heavy showers.
Sometimes in these thundery conditions, the rising air may be forced to "turn" because of variations in the strength and direction of the wind with height - a phenomenon known as "vertical wind shear". Occasionally this turning motion rapidly accelerates to result in a tornado. But why some thunderclouds spawn these devastating twisters, while other produce nothing more damaging than a shower of hail, is one of the few remaining mysteries of meteorology.
There is no indication that tornadoes are becoming more frequent over Ireland. Of course they may be, and such a tendency would not be inconsistent with the gradual rise in average temperature than has been a characteristic of the past decade, but there is no direct evidence that this is so. Nor is there anything significant in the fact that Dublin has been subject to attack; tornadoes can occur anywhere if the atmospheric conditions are right, and this time it just happened to be Dublin's turn.