What causes the turbulence when a jet aircraft is going through layers of clouds during takeoffs and landings?
—Lionel Chartier, Chicago
Turbulence is caused by random, continuously changing air motions that are superimposed on the wind.
A jet flying through any sharp boundary between differing air motions will experience “bumpiness.” This is most often caused by a current of air moving up adjacent to a current of air moving down. An aircraft will have a bumpy ride when it flies through the sharp boundary between opposing air motions. A sudden change in wind direction has a similar effect, as does a sudden change in wind speed.
Such sudden changes in vertical air motions, wind direction and wind speed are typical of air in clouds, especially cumulus clouds.