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A contrail, also known as a condensation trail,
is a cirrus-like trail of condensed vapor
(often resembling the tail of a kite) that is produced by
jet aircraft flying at high altitudes.
Contrails are produced at altitudes high enough for water droplets
to freeze in a matter of seconds before they
Temperatures at such altitudes are typically
below -38 degrees Celsius.
[Image: photo of contrail in tact (78K)]
through the injection of water vapor into the atmosphere by exhaust fumes from a
jet engine. If there is sufficient mixing between the cold upper tropospheric
air and the hot exhaust gases to produce a
state of saturation,
ice crystals will develop.
Even tiny nuclei
released in the exhaust fumes may be sufficient enough to generate ice
[Image: contrail spead apart by upper level winds (70K)]
Contrails spread apart and evaporate with time.
If the air in which the cloud develops has a low
the cloud particles will quickly evaporate. However, even in the presence of
higher relative humidities,
upper level winds can spread contrails apart,
forming a horizontal sheet-like cloud.
For a contrail to remain in tact for a long period of
time, the air must have high
a relative humidity and light winds.