Rattled nerves and spilled drinks are the most common outcomes of a choppy flight, but intense air turbulence can also cause bodily harm. And while one well-known cause of air turbulence is thunderstorms, it’s poorly understood how far from a tempest shaky conditions are likely to persist.
To answer that question, researchers recently analyzed millions of measurements of air turbulence collected by commercial aircraft. The team found that a heightened risk of a jarring flight extended more than 55 miles away from a thunderstorm, which is roughly three times the storm-avoidance distance currently recommended by the Federal Aviation Administration. These findings, published this month in The Bulletin of the American Meteorological Society, could inform new guidelines for storm avoidance, the researchers suggest.
Pilots and dispatch crews on the ground have long kept an eye trained on the weather. “The links between meteorology and aviation go way, way back,” said Stacey Hitchcock, an atmospheric scientist at the University of Oklahoma in Norman.
Thunderstorms are of particular concern to pilots. “You get really rapid changes in vertical and horizontal motion over short distances,” Dr. Hitchcock said. Those chaotic motions — which can also be caused by jet stream winds and air moving around obstacles like mountains — can cause aircraft to go up and down, creating the tumultuous sensation that’s all too familiar to many fliers.
In the past, daredevil pilots played a key role in revealing how aircraft experience turbulence near thunderstorms: A fleet of five P-61C Black Widow aircraft repeatedly flew through thunderstorms above Florida and Ohio in the 1940s. “No storm was to be avoided because it appeared too large or too violent,” a senior analyst for that endeavor, the Thunderstorm Project, later said at a meeting of the National Weather Association.
Today, however, scientists have access to troves of air turbulence data. “Almost all commercial aircraft now are collecting some form of turbulence data,” said Todd Lane, an atmospheric scientist at the University of Melbourne in Australia who was involved in the new research.
Dr. Hitchcock and her collaborators analyzed roughly 200 million such measurements made over United States airspace from 2009 to 2017. The team focused on the eddy dissipation rate, a metric related to the vertical acceleration experienced by a plane and its occupants.
Next, the team mined archival radar data to calculate the locations of thunderstorms. By comparing the positions of airplanes and thunderstorms in three-dimensional space, the researchers determined how the relative risk of experiencing light, moderate and severe turbulence changed based on the distance from a thunderstorm.
As expected, Dr. Hitchcock and her colleagues found that turbulence was much more likely when an airplane was near a thunderstorm. Flying within about three miles of a thunderstorm increased a flight’s risk of experiencing severe turbulence by nearly a factor of 20, the team determined. However, severe turbulence is also exceedingly rare: A plane would have to fly for seven days straight just to experience one minute of it, on average.
And the sphere of influence of a thunderstorm extended to significant distances, the researchers showed. “You can even go as far as 50, 60, 70 kilometers from a storm and still have double the risk of turbulence,” Dr. Lane said. Overall, the team found that the risk of experiencing light, moderate or severe turbulence remained above background levels up to 55 miles away from a thunderstorm.
Current F.A.A. guidelines for storm avoidance dictate that pilots maintain a horizontal distance of at least 20 miles away from a thunderstorm. The new findings could play a role in the revision of those guidelines. “I am having conversations with folks at the F.A.A.,” Dr. Hitchcock said.
But giving storms a wider berth would mean more rerouting of aircraft, which is no small feat in crowded airspace, said Mohamed Foudad, a turbulence researcher at the University of Reading in England who was not involved in the research. “It will be complicated to put more restrictions on these guidelines.”
Another possibility is that captains could opt to turn on the seatbelt sign earlier, when planes are farther from thunderstorms, Dr. Hitchcock said.
Passengers are already encouraged to keep their seatbelt on throughout a fight, and prompting them to buckle in earlier — and flight attendants to stay strapped into their jump seats — could help prevent turbulence-induced injuries. A report published by the National Transportation Safety Board found that of the 123 passengers and flight attendants seriously injured by air turbulence from 2009 to 2018, just one person was known to be wearing a seatbelt at the time.
“Maybe we just need to put the seatbelt sign on a little bit earlier,” Dr. Hitchcock said.
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