Clear-air turbulence, abbreviated “CAT,” occurs high in the atmosphere at the cruising altitude of passenger jets. CAT happens in clear sky conditions and where the wind direction and speed changes quickly with height. If you flew on a plane that experiences a jarring bumpiness and yet there are blue skies out the window, then you’ve experienced CAT. It is most common over mountains, near fronts and around the jet stream. It is also more common in winter than summer.
CAT is a major challenge for weather forecasters, particularly those who support aviation industries. Rules-of-thumb exist to steer airplanes around likely areas of CAT; however, airplanes fly into turbulence on a daily basis. In fact, a common way of knowing that CAT is present is for a plane to accidently fly through it and then report the experience.
CAT results in tens of millions of dollars in aircraft damage, as well as passenger and crew injuries. On Jan. 16, three people were injured on a flight over southern Illinois and Indiana because of severe turbulence. On Dec. 28, 1997, a flight from Tokyo to Honolulu experienced heavy turbulence over the Pacific Ocean, killing one person as the result of severe head trauma and injuring at least 102 passengers. Now you know why the airlines tell you to keep your seat belt fastened tightly at all times.
What does CAT look like? By definition, you can’t see it but new methods of identifying CAT from satellite observations are being developed and tested at the UW-Madison. Hopefully we’ll have some smooth flying in the not-too-distant future.