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| Image from the original article |
The northwestern Persian Gulf, imaged by the Terra satellite on Wednesday, February 11, 2015.
Linear clouds known as contrails, which form along the path of an aircraft and trail behind it, are human-made clouds consisting of countless tiny ice particles and water. They form when water vapour in the atmospheric layer through which the aircraft is flying condenses around tiny particles emitted during fuel combustion in the aircraft engines.
Water vapour produced by the combustion of aircraft fuel also contributes, together with atmospheric water vapour, to contrail formation. The original article states that formation of this type of cloud requires the temperature and relative humidity of the atmospheric layer to be below approximately −36.5°C and above 60 percent, respectively.
Depending on the exact values of those parameters, a contrail can persist from a few seconds to several minutes after it forms. During autumn and winter, when the atmosphere is colder, these clouds may therefore form at lower altitudes as well.
Because contrails resemble cirrus clouds, they are sometimes referred to as Cirrus aviaticus. At the time of the article, the author notes that the magnitude of their influence on climate change was not yet firmly established and that research was continuing at universities to better understand the climatic effects of this form of artificial cloud formation.