Linear clouds..what are ... and why do they appear in the sky?

Weather of Arabia - Sometimes clouds appear in the sky in the form of a long line, but they do not last long, and it is a phenomenon that can be seen anywhere when the sky is not overcast, so what is the reality of these clouds? And why does it appear?

How do linear clouds appear?

Linear clouds sometimes appear behind the path of aircraft, and they are clouds in the form of a line produced by the exhaust of the aircraft engine or changes in air pressure, and these clouds are called condensation tracks (Contrails) , and these condensation tracks consist mainly of ice crystals, and they usually occur at an altitude of several miles from The surface of the Earth where the paths on which planes fly.

How do aircraft exhaust traps form?

The exhaust that comes out of the aircraft engine contains water vapor, in addition to particles and other impurities that result from the combustion of fuel, as these particles act as condensation nuclei for the water vapor that comes out with the exhaust, and with lower temperatures at high altitudes, water droplets freeze to form ice crystals that are formed Including paths of condensation. Condensation pathways can also be formed by changes in air pressure in the air vortices behind the wing or in the air over the entire surface of the wing.

Exhaust condensation paths usually form at high altitudes (above 8000 m), where the air temperature is below -36.5 °C, and can form near the ground when the air is cold and humid, but these condensation paths form temporary clouds. They may remain visible for only a few seconds or only a few minutes, or they may last for hours, depending on the temperature and humidity at the altitude at which they form.

Some scientists have considered condensation pathways that remain for a longer time important to be studied because they increase the amount of clouds in the atmosphere, and can have an impact on the global climate, but this effect is uncertain, and a 2013-2014 study came with joint support from NASA and the Center The German Aerospace DLR and the Canadian National Research Council (NRC) note that biofuels can reduce the formation of condensation pathways, as biofuels produce fewer impurities and soot particles, which are the nuclei around which ice crystals form.

How do paths of condensation from changing air pressure form behind airplanes?

When the plane accelerates before takeoff, the air pressure above and below the wing of the plane changes, which generates lift force. The decrease in pressure and temperature across each eddy causes the water to condense, and these eddies appear as visible clouds, and this effect is usually more common on humid days. Wingtip vortices behind the tips of the wings can also sometimes be seen on the sides of aircraft during take-off and landing, as well as during the landing of the space shuttle.

Visible wingtip vortices usually contrast with fuel combustion condensation trajectories, where engine exhaust condensation trajectories appear at high altitudes directly behind each aircraft engine, and wing thrust vortices only occur at lower altitudes, as the aircraft moves slowly after takeoff. Or before landing, and where the air humidity is higher.