On a sunny day, when the sky is blue, you can especially clearly notice that the planes flying overhead leave behind white stripes. Where do these marks come from? Are they harmful to others? Why do they remain after some planes, but not after others? Let’s figure it out together.
Why does the plane leave a white trail
In order to understand the scheme of formation of white stripes from airplanes and helicopters, you can conduct a simple experiment.
On a hot day, take a bottle, pour water into it and put it in the refrigerator for several hours. If you pull out the bottle after the allotted time and put it on the table, you will soon notice how the plastic surface fogs up and water droplets form on the bottle.
What is this? it condensate! It appears due to the temperature difference: a cold bottle in a warm room will always cause such an effect. The same thing happens if you walk through the cold wearing glasses and then enter a warm room. Glasses will fog up immediately.
How is the condensation related to the white plane trail? It turns out directly. The white trail from airplanes and helicopters is called a contrail. At their core, these bands are clouds. Only it is not nature that creates them, but the aircraft engine.
The main reason for the appearance of a condensation trail is moist air and low temperature overboard. When fuel, kerosene, burns in the aircraft engine, hot jets of gas and steam are thrown overboard. And since during the flight at high altitude the temperature is about minus 40 degrees, this steam becomes condensate, turning into fog or small, small ice crystals.
Crystals evaporate more slowly than ordinary water. For this reason, the white plane trail remains in the sky for a very long time. At the same time, the higher the humidity of the climate and the colder it is overboard, the longer, thicker, brighter the white stripes are.
Why are some planes missing?
Sometimes you can notice that a plane or helicopter flies high, but does not leave white marks behind. With what it can be connected? It turns out that this phenomenon also has a reasonable explanation.
First of all, the presence of a condensation trail depends on the humidity of the air. Humid air is air that contains many, many small particles of water. Accordingly, at a high sub-zero temperature, they freeze if they are doused with hot steam from burnt fuel.
If the plane flies over a region with dry air (which means that there are practically no small particles of water in the air), then there is nothing to freeze overboard. The contrail from an aircraft in such areas will either not be at all, or it will be very pale and will quickly dissipate.
And yet, as a rule, a condensation trail does not form in airplanes and helicopters that fly low. This is because the air temperature overboard is not low enough and the water particles simply do not have time to turn into crystals.
By the way, in some northern regions, where the air temperature reaches minus 50 degrees and below, condensation (or inversion) a trail from an aircraft can form even during takeoff or landing!
White footprint and environment
If the white plane trails in the sky are clouds formed from condensation, are they harmful to the environment? In fact, scientists still do not have a clear answer to this question.
On the one hand, these contrails, which streak the entire atmosphere, prevent harmful ultraviolet radiation from the sun from penetrating the earth. And this means that the risk of accelerating global warming and general climate change on the planet is several times reduced.
Other scientists claim that the condensation trail is the first cause of the greenhouse effect. They believe that the air ceases to cool naturally, which leads to adverse consequences.