For as long as I can recall on my time on the internet, there has been much speculation as to what exactly those vapor streaks behind jets were – some particularly… creative imaginations suggest what we see on a sunny day emanating from planes is some mysterious gas… Or perhaps, its a chemical they’re using to brainwash us…right? Well, the science is actually fairly interesting, and is something you probably even see daily in the winter-time at ground level, or in the summer-time when you crack open a can of soda – so lets dig into what this whole “contrail” thing is about (and isn’t!).
The first thing to consider is the fact that when airplanes are at cruising altitude, (around 33,000 feet, on average, though they can fly up to 47,000 feet) the atmosphere they fly throughout is often very, very, cold – so cold, in fact, you wouldn’t make it long in those conditions if you were dropped and left magically levitating there.
It’s true – temperatures at this height can range from 20F on the WARM side, to as cold as -80F or colder in more typical situations – compare that to the around 60F on the ground back down here we see on average, and perhaps you get a bit of a better picture as to the variability in the atmosphere, especially in the vertical (CAPE, anyone?) This is the beginning of what causes contrails – the wildly supercooled environment of that atmosphere interacting with the stupendously hot engines doesn’t go without its byproducts; really, its just basic physics.
Have you ever breathed onto say, a cold window in the winter? Take note of how, when your breath comes into contact, the area around where you breathed condenses and moisture forms atop the surface. Using this breath example, a 98 degree mouth breathing upon a cold – say, 32 degrees, for instance – window on a cold day would, expectedly, form condensation; but what if we scale this principle up? This is where contrails come in.
Remember how I mentioned in the previous section that it’s sometimes as low as -80F at flight altitude? Well, those planes are often churning above 400F, which definitely makes our cold window example look like Childs play. Just like that example, though, you’re working with some very basic physics, the air is cold, and is suddenly heated up, so condenses – or in other terms, a cloud is born… a contrail! Like I said, simple physics, right?
Despite rumors to the contrary, these contrails really are harmless, as they’re overwhelmingly composed of water vapor – with that knowledge in mind, you may even find them beautiful in a way. With the right sunset angle, I know I do.
Very interesting and informative. I really did wonder about the contrails! Thanks! I am relieved to find out it’s nothing dangerous!