WEATHER:THE NORTHWESTERLY winds which brought ash from the Eyjafjallajökull volcano over Ireland resulting in the stoppage of flights yesterday, are set to dominate the weather until tomorrow evening, according to Met Éireann.
High pressure over the Atlantic is drawing winds from Iceland down over Ireland and they are not due to change until the second half of tomorrow, Met Éireann forecaster Evelyn Cusack said.
“A large area of high pressure to the west is bringing air directly down from Iceland over Ireland. It will stay in place for a couple of days, but by the end of Thursday northeasterly winds from Scandinavia will push the cloud away back over the Atlantic.”
The northeasterly winds should keep the ash cloud away from Irish and European airspace for the weekend. However it is likely to return next week with mid-range forecasts, which can predict weather up to 10 days in advance, showing a return of northwesterly winds, Ms Cusack said.
Whether or not the position of the cloud over Ireland results in the closure of airspace and cancellation of flights will depend on the concentration of ash.
The threshold for safe operations agreed by the aircraft engine manufacturers last month is .002 grammes of ash per cubic metre of air. The Volcanic Ash Advisory centre in London updates aviation authorities on the concentrations and the progress of the cloud every six hours with each update covering the following 24 hours.
Director of technology and training at the Irish Aviation Authority Philip Hughes said yesterday that this enabled a prediction to be made up to around midday today, “after that it gets a little more problematic”.
It is difficult to predict ash concentrations beyond this period as ash remaining in the upper atmosphere can take 10 to 14 days to descend. There is also new ash being generated from the volcano and it is a combination of these two sources of ash which can determine the concentration.
“There are new eruptions all the time, they are continuing, but not to the same level as initially, when there was glacial ice over the volcano which, when it erupted, resulted in steam which generated a very large plume of smoke.”
Haraldur Olafsson, professor in meteorology at the University of Iceland, yesterday said the most recent analysis of the volcanic ash cloud over Iceland showed a higher density of ash than expected.
“Another thing that surprised us was how dense the cloud was in spite of the distance travelled from the crater. The cloud top stood at about 12,000 feet and was far too dense for commercial aircraft,” he said.
Icelandic geophysicists monitoring developments under the volcano said the number and intensity of eruptions could be about to reduce. “Changes in pressure in the feeding channel of the volcano may precede a further reduction in the intensity of the eruption,” Sigrun Hreinsdottir, associate professor in geophysics at the University of Iceland said.