Tue 10 Oct 2017 – In May, 27 passengers on board an Aeroflot flight from Moscow to Bangkok were injured when the Boeing 777 encountered clear-air turbulence. Because the plane was unable to detect the turbulence ahead, passengers had not been warned to fasten their seat belts. There is evidence that clear-air turbulence (CAT) has already risen by 40-90% over Europe and North America since 1958 and studies by researchers from the universities of Reading and East Anglia in the UK have shown that as a consequence of climate change, the frequency of turbulence on flights between Europe and North America could double by 2050 and the intensity increase by 10-40%. The same researchers have since extended their previous work by analysing eight geographic regions, two flight levels, five turbulence strength categories and four seasons, and found large increases in CAT.
“While turbulence does not usually pose a major danger to flights, it is responsible for hundreds of passenger injuries every year,” said Luke Storer, a researcher at the University of Reading and co-author of the new study. “It is also by far the most common cause of serious injuries to flight attendants. Turbulence is thought to cost US air carriers up to $200 million annually.”
Previous research focused on turbulence over the North Atlantic region – one of the busiest air routes in the world – and suggested climate change will increase high-altitude wind instabilities in the jet stream in winter, generating stronger and more frequent pockets of CAT. Using supercomputer simulations of the future atmosphere, the new study analysed changes to CAT over the entire globe by the second half of the century.
The researchers found strong increases in CAT in all regions, in particular the mid-latitudes in both hemispheres where the busiest flights are in operation, and some regions may experience several hundred per cent more turbulence. They also found that of the five turbulence strength categories, the strongest turbulence will increase the most.
Flights to the most popular international destinations are projected to experience the largest increases, with severe turbulence at a typical cruising altitude of 39,000 feet becoming up to two or three times as common throughout the year over the North Atlantic (180% more common), Europe (160% more common), North America (110% more common), the North Pacific (90% more common) and Asia (60% more common).
The study also makes the first ever turbulence projections for the Southern Hemisphere, finding the amount of airspace containing severe turbulence is calculated to increase over South America by 60% and over Australia and Africa by 50%.
“Air turbulence is increasing across the globe, in all seasons, and at multiple cruising altitudes. This problem is only going to worsen as the climate continues to change,” said Paul Williams, Professor of Atmospheric Science at the University of Reading and lead author of the study.
He said the results highlighted an increasing need to improve operational CAT forecasts and to use them effectively in flight planning. “Despite containing useful information and demonstrably improving the safety and comfort of air travel, these forecasts continue to include a substantial fraction of false positives and missed events,” he added.
The study points out that future aeronautical advances, such as remote sensing of CAT using onboard light detection and ranging (lidar) technology, might be able to mitigate the operational effects of the worsening atmospheric turbulence. For example, Boeing is collaborating with the Japan Aerospace Exploration Agency to develop a system that will detect CAT more than 60 seconds, or about 17.5km, ahead of the aircraft (see Wired article). Even if it does not give pilots enough time to divert round the threat, it would alert crew and minimise the risk of injuries.
“Our findings may have implications for aviation operations in the coming decades,” say the researchers. “Many of the aircraft that will be flying in the second half of the present century are currently in the design phase. It would therefore seem sensible for the aircraft manufacturers to prepare for a more turbulent atmosphere, even at this early stage.”
The study, ‘Global response of clear-air turbulence to climate change’, is published in Geophysical Research Letters, a journal of the American Geophysical Union.
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