The big fluffy clouds, like from The Simpsons opening credits… Why, in real life, do they look like big puffy clouds sitting on a solid, smooth, invisible surface?
In: Planetary Science
As air rises, it cools down and eventually reaches a point where it has 100% humidity, at which point the water vapor in the air condenses. It is above this point that you can see the water vapor forming a cloud, but there is more water underneath that cloud, it’s just not condensed. So you could imagine a large vertical cloud, the bottom half of which is invisible to us.
You know how if your pour a cold drink after a short time the outside of the glass becomes wet? That’s because the glass became cold enough for water condensation to form.
Clouds are made of water condensation and need cold enough air to form.
And the air is different temperature at different heights. It gets colder as you get higher. Those flat bottom clouds are where the air directly below them is just slightly too warm for water condensation, so it makes a visible boundary.
Water vapor condenses into clouds when the air temperature is cool enough. The higher you go in the atmosphere, the cooler it gets. At some point as you rise higher, you hit the exact temperature at which condensation occurs. Below that point, no cloud. Above that point, cloud. That’s why clouds have flat bottoms.
Some clouds exist well above that point, so they are puffy on all sides. Sometimes the temperature all the way down at ground level is cool enough to create condensation, in which case we get clouds right here on the ground, and we call it fog.
They basically are. Cumulus clouds are the puffy ones that are flat on the bottom. There’s a layer of warm air below them where water can’t form into droplets because it’s too warm. As soon as the water passes that line, it becomes a part of the cloud.
That warm air rising contains the water that becomes the cloud, it just reaches a critical point in a relatively uniform way.
Similarly, cumulonimbus clouds (big thunderstorm clouds) are usually flat on top of the same reason. The warm air has reached too high and it has cooked enough to start sinking again.
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