The airport chaos that hit tens of thousands of travellers yesterday was based on a faulty ash cloud prediction.
Officials closed south-eastern airspace for ten hours following a Met Office alert about dangerous levels of ‘black’ ash.
Yet when the forecasters took fresh soundings, and sent up a plane to check, they found their assessment was flawed: there was no such ash.
So how did they get it so wrong?
By DAVID DERBYSHIRE
The decision to close the airspace over southern England was based on the word of an inaccurate Met Office computer.
It led again to angry complaints that airspace bans are based on theoretical models – rather than real-time.
The final word on whether to close UK airspace is made by officials at the Civil Aviation Authority. In turn, they rely on forecasts of the size, density and location of the Icelandic ash cloud provided by the Met Office’s volcanic ash advisory centre in Exeter.
There, a team of ten – including only one forecaster – work around the clock to monitor the movement of the ash cloud and run a computer model called NAME III.
The model converts data about the timing and location of the eruption, the height of the ash cloud, its likely composition and the prevailing weather conditions to predict its movement and density over the next 24 hours. The model takes 15 minutes to produce charts which are emailed to the CAA.
The Met Office insists it doesn’t just rely on its NAME model – and that it uses aircraft observations, ground-based radar called Lidar, weather balloons and satellite imagery to check its forecasts. It claims that its charts have been consistent with computer predictions from Canada and France
And it points out that the airline industry needs forecasts of the ash cloud to plan diversions.
But the model is only as good as the information it gets. And even the best Met Office weather forecast is only 70 to 80 per cent accurate.
See also: Aviation authorities criticised for unnecessary chaos
by Caroline Gammell, The Telegraph
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