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  • [MUSIC]

  • People have been looking at clouds since people have beenpeople. Those billowing shapes

  • might have been our first art or characters in our first stories. We still love to pick

  • out shapes, like bears, fish, flying saucers, faces, elephants. Some clouds even fly through

  • the sky like airplanes.

  • Which is weird because clouds are full of so much water that they can easily weigh as

  • much as a jumbo jet.

  • So why don't they fall out of the sky?

  • [MUSIC]

  • There's lots of different kinds of clouds, but in the most general weathery terms, clouds

  • are big fluffy piles of water vapor that live overhead. As warm, humid air rises through

  • the lower atmosphere, it expands, cools, and some of it condenses into very tiny liquid

  • droplets. And so a cloud is born..

  • Just how that water vapor rises, though, depends on the type of cloud. If the wind pushes it

  • up a mountain like it's on a ski jump, we might get lenticular clouds. Humid jet engine

  • exhaust can make wispy cirrus clouds.

  • But maybe the easiest cloud to understand is everyone's favorite fluffball: cumulus.

  • They're also the easiest ones to draw.

  • So how do you keep the weight of a hundred elephants in the air? Buoyancy! Warm air is

  • less dense, so it rises, just like inside of a lava lamp.

  • Cumulus clouds appear over dark pavement, fires, sunny hillsidesany source of warm

  • updrafts. As the water vapor in that air is carried up, it cools, so its molecules slow

  • down, and some of them stick together, forming droplets that we can see.

  • We still have an unanswered question though: After the wind carries them away from the

  • warm updraft, why don't clouds fall back down?

  • Because of condensation! You know how when sweat evaporates off your forehead, you feel

  • cooler? That's because water moving from liquid to gas takes some heat with it. Condensation

  • is just the opposite. It releases heat.

  • So as the water in a cloud condenses, it heats itself from the inside, staying aloft like

  • a hot air balloon.

  • Da Vinci called thembodies without surface”, which is why we can't live on them. But

  • maybe in them?

  • Lt. Col William Rankin did just thataccidentally anyway. As he was piloting his fighter jet

  • over the top of a massive cumulonimbus cloud, the engine caught on fire. He ejected and

  • fell from 47,000 feet straight into a 9 mile tower of lightning, thunder, ice, and rain,

  • carried up on 70 mph updrafts and barely conscious. He suffered from frostbite, bloodied from

  • the pressure change, bruised by hail, drowned by rain. What should have been a ten minute

  • parachute ride down to the ground instead took him 40 minutes.

  • He was definitely not on cloud nine. He was in it.

  • In the 1896 edition of the International Cloud Atlas, cumulonimbus, the world's tallest

  • and most powerful clouds, were placed at entry #9.

  • Unlucky pilots aren't the only living things inside clouds. Scientists found that living,

  • airborne bacteria make up as much as 20% of cloud condensation nuclei.

  • Not only are they home to airborne ecosystems, clouds are in some ways very much alive and

  • evolving themselves. Just take a few minutes and stare up at a fluffy cumulus, as its edges

  • billow and die. The rain that falls from them will one day rise again to become new clouds.

  • It's verycircle of life”.

  • LIVE TO GFX It might be because they're so alive that

  • their names sound like biological species. Cirrocumulus stratiformis! Cumulonimbus capillatus

  • incus!

  • Actually those sound like Harry Potter spells. Undulatus asperatus!

  • The greatest cloud photo of all time wasn't taken looking up at the clouds, but looking

  • down on them. When Apollo 17 astronauts brought this image back to Earth, it became the symbol

  • of a new environmental movement, demanding a new appreciation of our fragile planet.

  • 29% of its surface covered by land, 71% covered in liquid water, but so many clouds. There's

  • a lot that scientists still don't know about clouds but they are definitely important and

  • they look cool. Like Gavin Pretor-Pinney says, they are nature's poetry writ large for

  • all to see.

  • What's a sunset without the clouds? It's just a disappearing circle. I mean, a plain

  • blue sky? Would be justboring.

  • Clouds are what puts thepalein thisPale Blue Dot”. I like that.

  • OUTRO LIVE

  • I've got some homework for you this week.

  • [BOOING NOISES]

  • Gavin Pretor-Pinney is the founder of the CIoud Appreciation Society and author of this

  • book, The Cloudspotter's Guide. This book will completely change the way you look at

  • the sky, I can't even sit by the window on planes anymore, because it's too overwhelming.

  • Gavin wrote about a trick that I'm challenging all of you to do: go outside and lie on your

  • back so you can look up and behind you at the clouds. They become the landscape, and

  • the ground becomes the sky. If you see anything cool, take a picture and

  • let me know here.

  • I only scratched the surface of the cloud world today, but there's a link to this

  • book down in the description, it might be the best book on clouds out there. I've

  • also included a link to the International Cloud Atlas, so you can learn to identify

  • all those puffy white things in the sky, and also a link to a video about Lt. Col William

  • Rankin, The Man Who Rode the Thunder.

  • Thanks for watching, and stay curious.

  • [MUSIC]

  • Oh man, look at all these clouds, there's a stratus cloud, there's a nimbus cloud, those

  • are great. And a Cumulonimbus, whoa watch out for that one. You guys are totally putting

  • me in the clouds right?

[MUSIC]

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Why Do Clouds Stay Up?

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    綾羅飄起 posted on 2019/05/27
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