Photos of Contrails


Aviation fuel consists primarily of hydrocarbons. When the fuel is burned, the carbon combines with oxygen to form carbon dioxide. The hydrogen also combines with oxygen to form water, which emerges as steam in the exhaust. Contrails are condensation trails (vapour trails), cirrus clouds made by the exhaust of aircraft engines. The airplane's exhaust increases the amount of moisture in the air. This causes condensation to occur, and the contrail to form. (This is similar to what is happening when you breathe out in cold weather and see your breath. The difference is that, while condensation from your breath quickly evaporates, contrails at altitude tend to freeze and can take hours to fade away.)

Scientists identify two types of contrail, exhaust contrails and aerodynamic contrails. Exhaust contrails (described above) are the most common. Aerodynamic contrails are formed because the air moving over the plane’s wings causes a temporary reduction in pressure, which means the air can hold less water, so condensation occurs.
There is concern about the effect on climate of contrails, and studies have shown that they trap longwave radiation from Earth, which may contribute to global warming. Research suggests that night flights and flights in winter contribute the most in ground temperature rises.

Then there are people who believe in a conspiracy theory which says that some contrails are chemicals or biological agents being sprayed by clandestine government programmes. There is no scientific evidence for this theory.
The opposite of a contrail is called a ‘distrail’. This is when an aeroplane passes through a cloud and clears a trail. The temperature of the aircraft’s exhaust gasses absorbs water from the cloud, leaving a gap where the plane has been. ‘Distrail’ is short for ‘dissipation trail’.

(Contrails are not to be confused with ‘skywriting’, which is when an aircraft, usually a light plane, uses a smoke generator to write a message or draw a symbol in the sky, intended to be read by people on the ground. Often this skywriting is being used for advertising purposes, but the smoke usually disperses in a few minutes. Commercial skywriting was widespread in the 1930s before television advertising took over the mass market. Now the message is less likely to be about Pepsi or Ford, and more likely to be a local or even personal one, like “Eat at Joe’s Diner” or “Will you marry me?”)

Note: Contrails feature in popular culture too: there is a device on the market called Contrail that you attach to your bike and it leaves a trail of eco-friendly colours which fade in time and with rain.
There is also a German band called Contrails.....

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