Getting to grips with Irish twisters

CHARLIE TAYLOR

While tornadoes are primarily associated with the US, they are also recognised as part of the Irish weather pattern

FOLLOWING A WINTER in which it seemed as though storms were a constant companion, you’d be forgiven for concluding that the weather is getting worse. However, in the case of tornadoes at least, a sense of calm prevails. Not only has the number of tornadoes occurring declined over the past year but the strength of them has also decreased, according to Dr John Tyrrell, a climatologist at the department of geography at University College Cork and head of the Tornado and Storm Research Organisation (Torro), a privately funded body.

Presenting the results of a study into the occurrence of tornadoes in Ireland at Torro’s annual conference in Birmingham recently, Tyrrell revealed that while there was a substantial rise in the number of tornadoes reported last year, just four were declared genuine. While tornadoes are primarily associated with the US, Ireland has had as many as nine of them a year in the past, with some causing considerable damage.

Tyrrell, who has been studying tornadoes for more than a decade, relies on eyewitness reports, site investigations and weather observations from Met Éireann climate stations to help him uncover authentic tornadoes.

“I receive reports from various sources and then go out to the sites to carry out detailed investigation, during which I map the damage to trees, fields and buildings. This is then plotted and the results interpreted to establish whether the damage indicates a tornadic event,” says Tyrrell.

“I also take a look at the meteorological conditions which were present at the time, using data from the upper air and matching it with weather charts and radar. I also take eyewitness statements to gain additional information, such as dimensions of the funnel and whether it reached the ground or not.”

There were 18 reports of tornadoes around the country in 2008, along with eight reports of so-called mini-tornadoes and two “twisters”. However, after extensive investigations, it was established that only a fraction of these sightings were categorised as proper tornadoes.

Among the incidents which were discounted were reports from revellers of a tornado taking place at the Oxegen Festival at Punchestown last July.

The major event of the year was on Achill Island on January 4th, which started as a waterspout in the lee of Minaun Head. It came ashore at Keel as a tornado, reaching an intensity of T2 (up to 92 mph) and causing significant structural damage.

Tyrrell is keen to stress that a decline in the number of tornadoes in Ireland may be in part due to the fact that collection of data has improved in recent years, making it easier to conclude which events are genuine tornadoes.

“My research has been going on for the past 10 years, but I have also looked at historical records as well to measure the frequency of tornadoes in the past. We wouldn’t use those particular records to compute an average because we can’t be sure we have every possible event, but the material we’ve collated over the past decade is very reliable,” he says.

The strength of the four tornadoes which occurred last year across Ireland was in the range of T0 to T2. Ten years ago the annual range varied from T1 to T5 (core winds of up to 160 mph).

The temptation may be to attribute the decline in the number and strength of tornadoes to global warming, but Tyrrell is wary of doing so.

“Tornadoes aren’t just a product of temperature, it is a combination of processes. While most tornadoes occur during summertime, the most severe often take place during the winter,” he says.

The biggest recorded tornado in Ireland is believed to have occurred in Nenagh, Co Tipperary, on January 24th, 1852, when a tornado of T6 force (core winds of up to 180 mph) caused substantial damage.

The most unusual, meanwhile, took place close to the shore of Lough Carra in Co Mayo on July 31st, 2004, when a clockwise-rotating tornado occurred.

“In that particular situation the upper air flow was travelling faster than the lower air flow which created the funnel. As it came across the western mountains the spin was toppled up on end because of the big difference between the water temperatures of the lake and surface conditions. As the air rose it turned the funnel from horizontal to vertical and as a consequence affected its spin.”

While most reports of tornadoes turn out to be incorrect, Tyrrell still welcomes receiving them from the public.

“There have been situations where someone in a remote area might have been the only person to have seen a tornado but has been reluctant to admit to it in case their family and friends would think they were mad. If more people know about their existence then the more likely it is that they will report them,” he says. “And the more reports we receive then the greater knowledge we can build up about their occurrence in Ireland.”

Reports of tornado sightings can be sent to j.tyrrell@ucc.ie