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A contrail, also known as a condensation trail,
is a cirrus-like trail of condensed water vapor
often resembling the tail of a kite.
Contrails are produced at high altitudes where extremely cold
temperatures freeze water droplets
in a matter of seconds before they can evaporate.
[Image: photo of contrail in tact (78K)]
through the injection of water vapor into the atmosphere by exhaust fumes from a
jet engine. If the surrounding air is cold enough, a state of saturation
is attained and ice crystals develop, producing a contrail.
[Image: contrail spead apart by upper level winds (70K)]
If the air in which the contrail develops has a low
the cloud particles will quickly evaporate. Even in the presence of
higher relative humidities,
upper-level winds can spread a contrail apart
to produce a horizontal sheet-like cloud.
For a contrail to remain in tact for a long period of
time, the air must have a high
relative humidity in the presence of relatively light winds.