Contrails
Have you ever watched a jet or
an aeroplane fly across a clear blue sky? Sometimes it’s very easy to
trace their path because they leave behind a white streak across the sky
which fades after a while and disappears into the sky. These white stripes
are actually artificial clouds. They are called contrails or condensation
trails.
How are contrails formed?
As the plane goes higher the atmosphere becomes thinner and colder. Aeroplane engines produce exhaust just like a car engine does. The exhaust from the plane engine is much hotter than the surrounding atmosphere. As the hot exhaust gas escapes from the plane, the water vapour in the fumes hit the cold air (-40 oC).
The cold air causes the water
vapour to condense which in turn produces tiny droplets or freezes into ice
crystals before eventually evaporating. The mixture of condensed water
vapour and ice crystals make up the cloud like trails. This is similar to
the phenomenon we see when we breathe hot air on cold days.
Are contrails dangerous?
Contrails seen behind airlines are not dangerous. Their main composition is pure water. The jet fuels are also highly refined to remove as many contaminants as possible.
How are contrails helpful in weather prediction?
Contrails are classified into two distinct types: thin short-lived contrails and thick long-lasting contrails. The thin short-lived contrails are formed due to low humidity at high altitude, which is a sign of fair weather. The thick long-lasting contrails are formed due to the presence of highly humid air at high altitude which can be an early indication of a storm.
Is skywriting similar to contrails?
If you have ever seen an airshow, you must have seen the plane creating messages in the sky. This is called skywriting. They are not contrails.
The skywriters use small smoke machines in the plane to create written messages that are visible from the ground. The smoke machine contains oil, which when sprayed into the plane’s hot exhaust system quickly burns and creates dense white smoke.
Nowadays, skywriters take advantage of satellite navigation to program messages in order to increase the accuracy of what they are writing.
The opposite of contrails are distrails which is a rare phenomenon. People also consider contrails as chemtrails. What exactly are distrails? How are they formed? Are chemtrails the same as contrails? To get updates on these please visit our website.
– Suchasmita Panigrahi
