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Specific cloud types
Besides the commonly-found photos of relatively large-scale cirrus, stratus, and
cumulus clouds seen on the previous page, the sample
cloud photos on this page reveal chaotic and turbulent air flow that is usually
invisible to our eyes. Notice in this rotor
cloud how the eddy circulates 360 degrees or more. Although rarely seen,
the air flow pattern revealed by these cloud droplets is far more common than
most think and simply hidden from sight. Fast airflow over complex and steep
terrain increases the odds of seeing such a cloud formation. A more typical
rotor cloud appears like a long,
rolling cigar shape, sometimes with other eddies internally visible within the cloud.
Most air motions are more benign than these examples but can still be associated
with turbulence that aircraft passengers regularly experience. Other specific
cloud types often associated with turbulence and worthy of their own names
clouds, which sometimes appear like breaking ocean waves. The best examples of
K-H clouds are usually found in the lower or middle levels of the
atmosphere whereas cirrus-level clouds formed by the same instability are
termed billow clouds.
No matter their name, nearly all of these cloud forms are associated with
wind shear, which is just a term for changing wind direction and/or speed
Besides wind shear, the other primary mechanism to produce turbulence is
convection, which is responsible for a myriad of dramatic and beautiful
cumulus cloud forms. Within an immense cumulus cloud, an impressive example of
mammatus clouds blanketed
the sky overhead like an umbrella. Mammatus, also called mamma for short,
clearly derive their name from the same source as mammary glands. They
typically appear only when an especially strong thunderstorm has
matured and passed its peak intensity and are commonly seen in the U.S.
Great Plains states during severe weather season.
Storm chasers often encounter
impressive displays of mammatus clouds. Occasionally, these clouds appear
adjacent to intense hail and/or rain and nearly
reach the ground.
Another type of cloud usually associated with mountainous regions and wind shear
is altocumulus lenticular,
which have been mistaken for UFOs. They often look like a stack of pancakes or
plates and are created by moist air flowing over mountains. If conditions are
just right, there can be successive lenticular clouds as air rises, then descends
downwind of a mountain range, then rises again to form a second cloud farther
downwind. Then, as the sun sets, the bottom of these
clouds turn scarlet red.