Original title: Science Popularization | How dangerous is turbulence

Xinhua News Agency, London, May 23 (Reporter Guo Shuang) Singapore Airlines confirmed on the 21st that a passenger plane of the company flying from London, England to Singapore encountered severe turbulence during the flight, and landed in Bangkok, Thailand in the afternoon, resulting in one death and many injuries on board. People who often fly should be familiar with the turbulence of aircraft, but how dangerous is turbulence? How can passengers protect themselves to the greatest extent when encountering turbulence?

Generally speaking, when an aircraft crosses clouds or encounters strong airflow, it will experience turbulence. Turbulence can move an aircraft and cause sudden changes in flight altitude. Most of the turbulence occurs in clouds with updraft and downdraft, most of which are quite mild, but in some large clouds such as cumulonimbus clouds, the chaotic movement of air may lead to moderate or even serious turbulence.

There is another type of turbulence called "clear air turbulence", which occurs around the jet stream. The jet stream is a fast flowing air "river", which usually occurs in the height range of about 12 km to 18 km. There may be a speed difference of 160 kilometers per hour between the air in the jet stream and the surrounding air, which will lead to clear air turbulence. Its occurrence is not accompanied by obvious weather phenomenon, and there is no obvious boundary between the bumpy area and the non bumpy area, so it is difficult to be detected by pilots.

"We will feel a more bumpy sky, which I think may become a quite global phenomenon." Paul Williams, a meteorologist at the University of Reading, told Xinhua News Agency recently, "We now have strong evidence that turbulence is increasing significantly due to climate change."

"Our latest forecast shows that if the climate continues to change as we expect, the severe turbulence in the jet stream will double or triple in the coming decades," Williams said

Williams explained that among all kinds of turbulence, sunny turbulence is more difficult to deal with, because it will not appear on the weather radar in the cockpit, so there is less early warning.

The research team of Reading University led by Williams counted the flight conditions of several routes from 1979 to 2020, and found that the frequency of severe clear air turbulence on a usually busy route over the North Atlantic increased by 55% in these years. Regionally, the number of clear air turbulence on routes over the United States and the North Atlantic increased the most. Clear air turbulence on routes to Europe, the Middle East and the South Atlantic also increased significantly.

Nevertheless, it is rare to die in a commercial aircraft due to clear air turbulence. Williams said that the last death event caused by clear air turbulence occurred in December 1997, when a United Airlines Boeing 747 suffered clear air turbulence, resulting in the death of one person on board. After the accident, "other forms of turbulence have also led to deaths, but as far as I know, there have been no deaths caused by turbulence in commercial aircraft since 2009".

"Considering the number of commercial flights flying around the world, it can be said that the death caused by turbulence is extremely rare." Mark Proser, a British expert who studies turbulence, said, "turbulence is always a feature of flight. This is a natural feature of the atmosphere. You may encounter strong turbulence while flying, but the risk of death is still very small."

According to Gratton, associate professor of aviation and environment at Cranfield University in the UK, aircraft are designed to withstand the worst impact that turbulence may have on them, so turbulence is "unlikely" to destroy an aircraft. However, turbulence is not good for the aircraft, which is why pilots try to avoid it or slow down, and open seat belt signs to remind passengers to fasten seat belts.

When talking about what measures passengers can take to reduce risks, Proser pointed out that "it is much safer to fasten your seat belt. If you are especially worried about such things, you'd better try to fasten your seat belt during the whole flight, not just during takeoff or landing."

"Sometimes turbulence may come suddenly. Usually, when encountering turbulence, the crew will remind everyone to fasten their seat belts and hope that people can follow this advice. When encountering some more severe turbulence, the pilot will try to reduce or increase the altitude to avoid the sky." Proser said.