|Turbulence is the up-and-down air currents that help to mix the air in the
troposphere. It is usually mentioned in the context
of airplane flights, where these air currents can feel like "bumps in the road" while flying.
occur in the lowest part of the troposphere during the daytime when heating of the sun causes
convective mixing of the air. Once the airplane rises
above this turbulent "boundary layer", the air becomes smoother.
But other processes can also
cause these up- and down-drafts. One example is convective clouds.
If an airplane must fly through a thunderstorm, these updrafts and downdrafts can be very strong.
There is also "clear air turbulence", which can also become very strong. This usually occurs
near jet streams, where rapidly changing wind speeds with
height can combine with an unstable air layer to cause "waves" of up and down motion in this air layer.