Dodging ash clouds

Ash Clouds

When Chile's Puyehue volcano belched ash into New Zealand airspace in June and July, MetService's robust monitoring enabled Air New Zealand to keep flying safely.

MetService had just 36 hours' warning that the ash was heading New Zealand's way. The southern Andean mountain erupted with the power of 70 atomic bombs, expelling one hundred million tonnes of ash, sand and pumice stone into the atmosphere. Wind blew the cloud eastwards where it shut down most of South America's air traffic before drifting across the southern oceans towards Australia and New Zealand. MetService models that predict the dispersal of volcanic ash were configured for local eruptions; ash from half a hemisphere away was new.

MetService immediately made contact with the airlines, Civil Aviation Authority (CAA) and Airways. Two forecasters worked extra shifts to bolster its 12-strong aviation forecasting unit, which doubles as one of the world's nine Volcanic Ash Advisory Centres (VAAC). They kept in close contact with their colleagues in Darwin VAAC and marshalled data from weather models, satellites and ceilometers that shoot lasers skyward to detect atmospheric particles.

Pilot observation was helpful too. However, calls from the flight deck became scarcer as international flights were cancelled. What some pilots initially thought was volcanic ash turned out to be haze.

MetService collated and verified every scrap of information about the ash cloud according to clear protocols. For more than a month, it issued advisories and SIGMETs (the equivalent of severe weather warnings) to CAA and the airlines. With the ash cloud verified at 30,000ft, Air New Zealand flew under it and re-routed some flights, absorbing the extra fuel costs. No planes encountered the ash cloud and there were no safety incidents. When MetService predicted the ash would drift down to 10,000ft over the South Island, the airline grounded a handful of domestic flights, its only cancellations.

When the skies eventually cleared, CAA thanked MetService for "excellent and rapid support" in observing and validating the ash and keeping the aviation industry informed. "Forecasters handled this event in a thoroughly professional and timely manner," said Keith Mackersy, CAA's Technical Consultant, Meteorology. New Zealand's flying public were the winners.

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