Contrails | |
---|---|
Genus | Cirrus (curl of hair), cirrocumulus, or cirrostratus |
Altitude | 7,500 to 12,000 m (25,000 to 40,000 ft) |
Classification | Family A (High-level) |
Appearance | Long bands |
Precipitation | No |
Contrails (/ˈkɒntreɪlz/; short for "condensation trails") or vapor trails are line-shaped clouds produced by aircraft engine exhaust or changes in air pressure, typically at aircraft cruising altitudes several kilometres/miles above the Earth's surface. They are composed primarily of water, in the form of ice crystals. The combination of water vapor in aircraft engine exhaust and the low ambient temperatures at high altitudes causes the trails' formation. Impurities in the engine exhaust from the fuel, including sulfur compounds (0.05% by weight in jet fuel) provide some of the particles that serve as cloud condensation nuclei for water droplet growth in the exhaust. If water droplets form, they can freeze to form ice particles that compose a contrail.[1] Their formation can also be triggered by changes in air pressure in wingtip vortices, or in the air over the entire wing surface.[2] Contrails, and other clouds caused directly by human activity, are called homogenitus.[3]
Depending on the temperature and humidity at the altitude where the contrails form, they may be visible for only a few seconds or minutes.[1] Persistent contrails are of particular interest to scientists.[1] The resulting cloud forms are formally described as homomutatus,[3] and may resemble cirrus, cirrocumulus, or cirrostratus, and are sometimes called cirrus aviaticus.[4] Some persistent spreading contrails contribute to climate change.[5]
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