When the weather is relatively clear, there will be airplanes pulling a long white line in the sky.

A natural phenomenon, called aircraft cloud, is formed:

Only when a jet aircraft flies in an air layer below -20°C and the air humidity is close to or reaches saturation , and at the same time, tail smoke, that is, wake cloud, can be produced only when the atmosphere is relatively stable.

The principle behind the formation of wake clouds is: when a jet plane flies at a very cold altitude with a high water vapor content, the hot air ejected from the tail of the plane condenses into a cloud band when it encounters cold in the low-temperature and high-humidity air.

Another process that produces contrail clouds is when an aircraft flies in nearly saturated air, and the air near the tips of the propellers and wings condenses due to adiabatic cooling due to power decompression, but this situation is relatively rare. .

Generally speaking, airplanes tend to form wake clouds at altitudes between 10,000 meters and 7,000 meters. Beyond this range, airplanes will not produce "smoke" phenomena.