What happens next depends on how dry or how humid the air is.
If the air is very dry, the ice crystals will sublime change phase directly from solid to gas and become invisible. If the air is humid, the water droplets or ice crystals will stay where they are, often spreading out, leaving a fluffy trail where the aircraft has passed. Trails may last for many hours leaving the sky criss-crossed with lines, and mixing with cirrus cloud. Contrails are not large enough to cause any weather on the ground.
We tend to observe them in empty skies in high pressure situations when there are very few other clouds around. The reduction in pressure and temperature across each vortex can cause water to condense, producing a thin line of water droplets that looks just like a contrail.
This effect is more common on humid days so wingtip vortices can sometimes be seen behind the wing flaps of airliners during takeoff and landing. Unlike contrails, wingtip vortices are usually only seen at low altitude where the aircraft is travelling slowly after takeoff or before landing. They trail behind the wingtips and wing flaps rather than behind the engines, and they evaporate quickly just a few metres behind the aircraft.
Where an aircraft passes through a cloud, it can disperse the cloud in its path. This is known as a distrail short for "dissipation trail". The plane's warm engine exhaust causes existing water droplets in pre-existing clouds to evaporate, leaving a clear wake through an otherwise cloudy sky.
Do you know the difference between a chemtrail and a contrail? A contrail is an abbreviation for " condensation trail," which is a visible white vapor trail produced as water vapor condenses from aircraft engine exhaust. Contrails consist of water vapor or tiny ice crystals.
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The length of time they persist varies from several seconds to a few hours, depending largely on the temperature and humidity. Chemtrails , on the other hand, are "chemical trails" purportedly resulting from an intentional high-altitude release of chemical or biological agents. While you might think chemtrails would include crop dusting, cloud seeding and chemical drops for firefighting, the term is only applied to illicit activities as part of a conspiracy theory.
Proponents of the chemtrail theory believe chemtrails may be distinguished from contrails by color, displaying a criss-cross trail pattern and persistent appearance. The purpose of chemtrails might be weather control, solar radiation control, or testing of various agents on people, flora or fauna.
Simon Patterson ft. Dave Wright - Vapour Trails by Simon Patterson | Free Listening on SoundCloud
Atmospheric experts and government agencies say there is no basis for the chemtrail conspiracy theory. Even if it's assumed contrails serve no nefarious purpose, it's worth asking whether they impact the environment and whether they are potentially harmful. To answer this question, it's useful to understand how contrails form. An aircraft with a jet engine burns fuel and releases an exhaust plume into the atmosphere.
The composition of the fuel is tightly regulated to minimize impurities, but may contain a small fraction of nitrogen or sulfur. Combustion releases carbon dioxide and water, two important greenhouse gases. Sulfur particles provide nuclei on which water vapor may condense into droplets.
Incredible images of vapour trails and sonic booms created by planes in the sky
The collection of droplets appears as a contrail. Basically, a contrail is an artificial cloud. Criss-crossing contails occur in high traffic areas. If on the other hand, the winds are strong and the moisture content low, then dry surrounding air vigorously infiltrates the cloud, facilitates evaporation, and the contrail breaks up and dissipates with great rapidity.
The type of aircraft has an impact, too.
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If the engines are slung below the wing - as, for instance, in the case of a Boeing - the aerodynamics are such that the exhaust gases are drawn into the wing tip vortices - the spirals of air which trail behind an aircraft. In these circumstances the contrail tends to form at the core of the vortex, and is protected by the whirling tube from incursions of drier air.
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