Smooth flying: Breakthrough in understanding gravity waves could help pilots predict and avoid turbulence, scientists say

Chinese team learned more about invisible ripples in space by studying thunderstorms

PUBLISHED : Tuesday, 20 October, 2015, 12:02pm
UPDATED : Tuesday, 20 October, 2015, 3:59pm

Thunderstorms can generate strong gravity waves that are able to travel long distances and even potentially affect an aircraft far away in clear conditions, according to a new study by Chinese scientists.

The findings shed new light on one possible mechanism behind clear-air turbulence, and might help researchers come up with forecasting methods to reduce unexpected bumps in flights.

Clear-air turbulence is mostly harmless, apart from the mental strain it puts flight passengers under. But it can trigger travel sickness, and in extreme cases fliers can find themselves tossed around or even severely injured.

Because clear-air turbulence cannot be detected by the naked eye and is also very hard to spot using radar, pilots are often not alerted to its presence until they are almost in its midst.

Researchers have investigated many possible causes, such as jet streams and wind shear, but no satisfactory explanation has yet come to light to unravel the phenomenon.

In recent years, some investigators have focused on gravity waves. They compared these invisible waves to the ripples that emanate outwards when a stone is thrown into a pond.

Using the world’s largest network of airglow observatories, the Chinese team used sensitive optical devices at night to monitor the faint light emitted by the atmosphere in North China in 2012.

By measuring distortions to the nightglow, the scientists thought they would be able to work out the propagation pattern of the gravity waves.

“Through our observations, we have collected troves of valuable data that will significantly help our understanding of the nature of gravity waves,” said Xu Jiyao, who led the study.

Xu has been working with the Center for Space Science and Applied Research at the Chinese Academy of Sciences.

“We hope our research will help solve the mystery of atmospheric turbulence and [gravity] waves,” he said.

The network of observatories consists of over a dozen ground-based stations, which means it can document how gravity waves evolve in a way that is difficult to do using satellites.

In their latest paper, published in the Journal of Geophysical Research: Atmospheres, Xu and researchers from the US and Germany reported their observations of two extreme thunderstorm events in the summer of 2013.

They hoped these may contain important clues about the strong atmospheric perturbations such storms produce.

From one of the storms, they discovered that gravity waves can travel up to 1,000km without significant energy loss, much like a train going through a tunnel.

They also learned that two thunderstorms can create certain conditions, or “breaks” in the air, where the gravity waves become especially intense.

Chinese scientists can now record the changes in gravity generated by thunderstorms all over the country, from the high peaks of mountains in Tibet to the tropical forests of Hainan island, Xu said.

Combining the data from ground-based stations and satellites, researchers may be able to develop meteorological models to predict when and where atmospheric waves and turbulence will occur in the future, he said.

Aeronautical scientist Cheng Wei said the new research will help improve the safety and comfort of air travel.

“Gravity waves are a relatively new concept to most plane designers,” said Chen, who works at Beihang University, a top aircraft research institute in the Chinese capital.

“They be a source of discomfort to fliers, but they haven’t really been taken into account during the design and manufacturing of planes before, because we know so little about them,” he added.

“Maybe plane designers and atmospheric physicists can work together on the problem. The priority should be to collect as much data as possible on the subject.”