How do contrails form?
It was good weather today, so Mika and I decided to take a walk in the nearby garden. After a long walk, we were just lying on the grass, watching the sky, when we saw long white streaks stretched far across the blue sky, and then just from the other side, there was an airplane passing which was leaving behind this white line, just like someone had drawn white chalk lines across the sky. That made me wonder—why do some airplanes leave these trails while others don’t? It’s not something we see every time an airplane passes.
Are these trails of smoke coming from the engines? Or do airplanes paint the sky?
I asked Komal, who researches the atmosphere. Komal asks if I’ve ever noticed how my breath turns into mist on a cold winter day. I nod, and she smiles, saying that these long white trails form in a similar way!
High up in the sky, where airplanes fly, the air is much colder than at the ground—sometimes colder than –40°C! When an airplane engine burns fuel, it releases hot gases, including water vapor. When this warm water vapor meets the freezing air, it condenses into tiny water droplets or ice crystals—just like how my breath turns into mist on a chilly morning. This creates the long, white trails we see in the sky, called contrails, short for “condensation trails.”
She also explains that there are three types of contrails:
1) Short-lived contrails – These form behind an airplane but disappear quickly if the air is dry.
2) Persistent non-spreading contrails – These stay in the sky as thin, white lines for minutes or even hours when the air is very humid.
3) Persistent spreading contrails – These grow wider and fuzzier over time. Sometimes, they even turn into cirrus-like clouds and can last for hours, covering large parts of the sky!
Wow! So contrails are actually human-made clouds! The next time I see one, I’ll know it’s not smoke but tiny ice crystals floating in the cold air. And if the contrail stays in the sky for a long time, I’ll remember that it could tell me something about the moisture up there!
