Reported January 2008

WHAT IS TURBULENCE? Air is a gas and water is a liquid, but scientist lump both into the category of fluids. A material is considered a fluid if the amount of force needed to change its shape is dependent on how quickly it changes. For a solid, the force needed to change its shape is dependent on how much it changes. For example, it takes the same amount of force to break a twig quickly as it does to break it slowly. But moving your hand through a body of water quickly will deform the liquid more than if you moved your hand through it slowly. The same phenomenon happens with air, as anyone who has ever stuck a hand out the window of a fast-moving car can attest.

Turbulence is what happens when the flow of air experiences a sudden change in wind speed or direction. This makes it bumpy instead of smooth. We can see turbulent flow in rivers and streams, or even when we stir cream into our morning cup of coffee. And most of us have experienced mild turbulence while flying in an airplane; the plane is flying through a "sea" of air, and sometimes the "waves" are choppy. Many things can cause turbulence: rising warm air, thunderstorms, even strong winds blowing over the tops of mountains, buildings and other objects in its way. Extreme turbulence is caused by severe thunderstorms, tornadoes, or hurricanes; airplanes usually divert their courses to avoid such areas.

Turbulence on flights can be annoying, but passengers are usually safe so long as they keep their seat belts fastened. The bumps and jolts don't really affect the aircraft or its flight path, unless the turbulence is quite severe. Severe turbulence can be avoided by flying around storm cells, or changing to a higher altitude.

If you would like more information, please contact:

John Williams
Mathematician
National Center for Atmospheric Research
(303) 497-2822
jkwillia@ucar.edu