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Good volcanic ash data saves European air traffic

Foto: NASA, GSFC, MODIS Rapid Response Team

Article from NILU’s Annual magazine 2011: Three days after a volcanic eruption in Iceland in May 2011, the Met Office in London warned that volcanic ash in the skies over large parts of southern Norway could represent a danger to air traffic. But Norwegian experts had their own models and good satellite data and concluded that air traffic could resume as normal.

By Bjarne Røsjø

Kjetil Tørseth
“It was primarily observational data from satellites that enabled us to have good enough estimates of the ash concentrations from the eruption,” says Kjetil Tørseth, director of the Department for Atmospheric and Climate Research at NILU. Photo: Ingar Næss

When Iceland’s Eyjafjallajökull volcano erupted in April and May 2010, hurling vast quantities of ash into the atmosphere, both Norwegian and international aviation authorities were poorly prepared. It had been a long time since anything like this had happened in Europe, and the ash cloud from Eyjafjallajökull grounded more planes than any previous volcanic eruption. Millions of airline passengers remained “trapped by volcanic ash”, and the airlines lost huge amounts of money.

But when Iceland’s Grimsvötn volcano in Iceland erupted a year later, on 21 May 2011, both the Norwegian and international aviation authorities were far better prepared. On Tuesday 24 May, the London Volcanic Ash Advisory Centre (VAAC), based at the UK Met Office, warned that the airspace above Haugesund, Stavanger and Kristiansand forecast high enough concentrations of ash so that it would be inadvisable to fly, and making it likely that thousands of passengers would be stranded starting at 14.00 that day.

An emergency meeting

In spite of these warnings, Norwegian air traffic was able to continue as normal because the country’s aviation authorities had entered into a unique collaboration with a number of Norwegian research institutions. Experience from the Eyjafjallajökull eruption led the Civil Aviation Authority to established Agency Volcanic Ash Group (EVA), with representatives and experts from the Civil Aviation Authority, Avinor, the Norwegian Meteorological Institute and the Norwegian Institute for Air Research (NILU).

When the Grimsvötn volcano erupted, EVA members were called into an emergency meeting, where scientists were able to present reliable satellite data on the probability that the airspace over the southwestern part of Norway would not be subject to high concentrations of ash.

This was a historic decision: Norway was the first country in Europe that chose to rely on its national expertise instead of warnings from the VAAC, and the Civil Aviation Authority allowed air traffic to proceed normally in an area where the VAAC had warned that ash concentrations would be unacceptably high. This decision resulted in savings for airlines and prevented a great number of travellers from suffering the inconvenience of being unnecessarily grounded.

The ash cloud that ascended into the atmosphere right after the eruption of Grimsvötn in May 2011 Photo: Wikimedia commons, Calistemon

The Agency Group’s decision was sent to the airlines just minutes before air traffic over large parts of southern Norway would have been paralyzed. The EVA subsequently had daily meetings until the volcano’s eruptions calmed down, and it turned out that the Norwegian forecasts were accurate. Norwegian airlines thus avoided significant economic losses from rescheduling several hundred flights, while air traffic over Iceland, northern Sweden, Denmark, Germany and Scotland was hit hard.

Satellite data kept the air space open

“It was primarily observational data from satellites that enabled us to have good enough estimates of the ash concentrations from the eruption. EVA is a concrete example of how good working relationship between the research community and regulatory agencies can provide results that benefit society,” says Kjetil Tørseth, director of NILU’s Department of Atmospheric and Climate Research.

NILU has studied the spread and detection of volcanic ash clouds for a number of years, and has monitored the spread of ash clouds with the aid of satellite-borne instruments that were originally designed to detect radiation and clouds. “Researchers at NILU have developed methods that make it possible to use data from these instruments to determine whether there is ash in the atmosphere. These algorithms proved their worth when the Grimsvötn volcano erupted in May 2011,” Tørseth says.

The Eyjafjallajökull eruption in 2010 led to several changes in international aviation authority regulations. “When Eyjafjallajökull erupted, regulations were issued that prohibited commercial flights if there was any ash whatsoever in the air. But this was too restrictive, so threshold levels were established that would allow planes to fly in low levels of ash if certain procedures were followed. In May 2011, the VAAC in London forecasted that these threshold limits could be exceeded in southern Norway, while our satellite data showed lower ash concentrations than the limits,” Tørseth said.

Although the Norwegian government chose to ignore the VAAC advice to close the air space, it does not mean that the watchdogs in London did a bad job. Providing forecasts of ash concentrations is actually a very difficult task.

“Bringing in national, in addition to international expertise, provided an improved basis for decision-making. In addition, this made it possible to take advantage of local knowledge and made for closer proximity to the important decisions that had to be taken,” Tørseth said.