Although there are many conspiracy theories generated by this phenomenon, the explanation of what they are is rather mundane: contrails are water vapour. Yes, it’s that simple. Following, we expand a little.
The first thing we need to take into account is that clouds are formed when a mass of air condensates, that is, when its humidity reaches 100%. In order for this to occur, temperature plays a major role: the lower the temperature, the easiest it is for air to reach the condensation point.
To give an example, at sea level, a mass of air at 75% humidity and at 15º C will not condensate, however, if temperatures were to descend to 5ºC, it would. As we know commercial aeroplanes fly in the highest layers of the troposphere at temperatures around -56ºC, there is no need to explain further, is there?
The other essential factor for the formation of contrails is the way turbine engines work. In the same way as cars do, aeroplanes use combustion engines which generate thrust force burning fuel and oxygen.
As a result of this process, a number of gases are generated during combustion, amongst them, water vapour. Along with low temperatures these go on to form great water vapour trails or contrails.
In English, contrail is the contraction of condensation and trail. In Spanish we have adopted this anglicism due to its simplicity and briefness, although the correct term is `estelas de condensación´.
You may now be thinking: What about the colour trails that can be seen in air shows? Well, these aren’t contrails.
We need to take into consideration that this type of acrobatic flight is performed at low altitudes so they can be enjoyed at a glance and to add to that, they usually take place in summer, when temperatures go up and the weather’s good.
Colour trails of acrobatic airshows are achieved through intentional processes which are controlled by the pilot according to the manoeuvre they are performing. The singularity and surprise element that colour trails bring and that is characteristic of these events, is obtained through mixing colourings.
