Hey!
So i was juste outside looking at the sky and there are many clouds out right now, they’re all of many different sizes and shapes but they all share one common trait. Their underside is flat. I thought it may just be the perspective or lighting but if that’s the case then it’s a very convincing illusion because they all look like they have a flat bottom…
is there a reason for this or is it actually not the case?
In: Physics
You are probably talking about cumulus clouds. These clouds form when the water vapor (which is invisible) rises above a certain altitude, where the temperature is low enough for it to condense into droplets of water, that form the cloud. This horizontal border is what we see as the flat bottom of the cloud.
There’s kind of a floor that clouds form on top of. It’s dependent on a lot of factors, like temperature and humidity and air pressure. If you’ve ever been up in the mountains, you sometimes see clouds below you in the morning, and as the day progresses and the earth heats up, the cloudes rise higher as the level of that “floor” rises.
So they are flat on the bottom because there’s an elevation below which the cloud can’t exist.
For a cloud to form, you need to have more water in the air than the air can hold as a gas, which causes droplets to form which are the clouds you see. How much water the air can hold as a gas depends on temperature, and temperature decreases fast as you go up, but changes relatively little horizontally making a flat cloud bottom at a certain temperature level.
This level is called the lifting condensation level, or LCL, if you want to learn more!
Imagine you have a balcony full of small glowing balls. Some of them are close to the edge. Too close and they fall off. Now make it dark. The glowing balls form a very straight edge that is also the edge of your balcony. You can’t see the balcony but you can see the glowing edge.
You can’t see water vapor but you can see “cloud”.
Clouds have a minimum height to be at. Anytime a part of the cloud is a little lower, it cannot be a cloud anymore. And so you see the flat bottom as the minimum height where clouds can be.
It heavily depends on weather conditions, which is why sometimes clouds are higher up than on other days.
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