The white grooves left behind by airplanes in the sky, also known as contrails or defractory trails, are a result of a complex equation involving several factors. First and foremost, clouds form when the humidity in the air reaches 100%, which can only occur at extremely low temperatures. Commercial airplanes typically fly in the highest layer of the troposphere, where temperatures average around -56°C.
Secondly, the engines on these planes play a significant role in creating contrails. Airplanes use their engines to generate thrust force and burn fuel and oxygen to do so. The water vapor produced by this process is much hotter than the surrounding air, causing it to condense and create the snowy lines that we see behind planes. Additionally, as gases expand when they leave the plane’s engine, this also contributes to the formation of contrails.
The term “contrail” was coined by Anglo-Saxons as a combination of “condensation” and “trail.” It raises an interesting question: why not all airplanes leave a trail? The efficiency of a turbojet is determined by its ability to convert chemical energy into work output. In terms of contrails specifically, their nature and persistence can be used to predict weather conditions.
During air shows, you may notice that some contrails are colored rather than white. These “polychrome grooves” are created by mixing dyes and releasing them at just the right moment. As a result, they are not true condensation trails but rather intentional displays put on for spectators. Finally, there is an impressive type of contrail formed by airplanes traveling faster than the speed of sound: these clouds take on a disk or cone shape due to sudden drops in air pressure caused by supersonic flight.