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Contrail

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Article Information
Category: Weather Weather
Content source: SKYbrary About SKYbrary
Content control: SKYbrary About SKYbrary
WX
Tag(s) Cloud Formations

Condensation Trail

Description

A trail of cloud which forms behind an aircraft flying, usually at high level, in moist and very cold air.

condensation trail
The contrails of a four engined jet, over London, England

How Contrails are Formed

One of the main constituents of exhaust gasses emitted by a jet engine is water vapour. This has the effect of increasing the humidity of the layer of air that an aircraft flies through. In certain conditions, if the humidity is raised beyond saturation, a trail of cloud forms behind the aircraft. This condensation trail is known as a CONTRAIL. The critical temperature, below which Contrails may form (MINTRA, minimum trail), is approximately -24°C at Sea Level and -45°C at 50,000 feet. However, the heat generated by the engine raises the temperature in the wake of the aircraft and consequently lowers the relative humidity so jet aircraft do not necessarily generate contrails unless the temperature is approximately 15°C below the MINTRA temperature. In broad terms, Contrails are more likely in a warm Tropical Maritime air-masses with a high but cold tropopause, whereas Contrails are less likely to be seen in cold, polar air-masses with a low, relatively warm tropopause.

Hazards

Since a Contrail indicates where an aircraft has been, their existence may be an indication of potential Wake Vortex Turbulence.

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