June 26, 2012 Aircraft turbulence guidelines should be completely rewritten after new research revealed thunderstorms could produce unexpected turbulence more than 100km away from storm cells.
The research by University of Melbourne and the Centre of Excellence for Climate System Science researcher Dr Todd Lane has highlighted the impact of atmospheric gravity waves caused by thunderstorms and how air safety guidelines have not taken them into account.
"It is likely that many reports of encounters with turbulence are caused by thunderstorm generated gravity waves, making them far more important for turbulence than had previously been recognized," Dr Lane said.
"Previously it was thought turbulence outside of clouds was mostly caused by jet streams and changes in wind speed at differing altitudes, known as wind shear, but this research reveals thunderstorms play a more critical role," he said.
Dr Lane said it is now recognized that thunderstorms have far reaching effects, modifying airflow, strengthening the jet stream and enhancing wind shear at a significant distance from the storm cell itself.
Flights along domestic Australian routes and international routes across the tropics towards Asia and between Australia and the US regularly detour around storm cells. However, this research indicates they may still be close enough to encounter gravity waves and clear-air turbulence.
This unexpected turbulence mid-flight can lead to passenger injuries. Around 97 per cent of injuries caused by turbulence during flight occur because people are not wearing seatbelts. On average, around 15 people are injured every year due to turbulence.
Beyond the immediate safety concerns, it has been estimated that turbulence costs the aviation industry more than $100M a year globally due to associated rerouting and service checks.
Despite this, little research is being done worldwide on near-cloud turbulence according to Dr Lane, even though improvements in high-resolution atmospheric modelling could generate important advances.
"Ten years ago, we didn't have the computing power and atmospheric models to answer some of the important questions around turbulence," Dr Lane said.
"Now we can answer some crucial questions but there are only a few groups working on this problem. We need more researchers to become engaged to improve the guidelines and passenger safety."
Currently, many of the world's guidelines for flying around thunderstorms -- including Australia's -- are similar to those produced by the US Federal Aviation Administration (FAA). However, these guidelines do not include information about atmospheric wave processes.
"We are working hard to develop new guidelines to recommend to the FAA that include a proper representation of the physics,"Dr Lane said.
"We now know a lot more about how thunderstorms cause turbulence than we did when the guidelines were originally introduced."
"It is time to alter air turbulence guidelines in light of this knowledge and employ new technologies to forecast where it is likely to occur to improve air safety for all air travellers."
The work was funded by the Australian Research Council and published in the Bulletin of the American Meteorological Society.
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- Todd P. Lane, Robert D. Sharman, Stanley B. Trier, Robert G. Fovell, John K. Williams. Recent Advances in the Understanding of Near-Cloud Turbulence. Bulletin of the American Meteorological Society, 2012; 93 (4): 499 DOI: 10.1175/BAMS-D-11-00062.1
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