And what causes them to suddenly drop all of that water in the form of rain.
Judging by the amount of rain they must weigh a ton.
In: 337
Ph.d Meteorology student here. Clouds are really just areas of our atmosphere that are “supersatured” with respect to liquid water (this can happen for ice too, depending on temperature). Think about when you get out of the shower, the room is foggy, and that’s because of a lot of water vapor entering the air through the faucet and that vapor is condensing onto aerosols in the air causing you to visually see it. This is a cloud, similar to those in the sky. Sure, the total liquid water content is a lot in real clouds, but they aren’t solid objects. They are just a bunch of liquid (or ice) droplets being suspended close together in proximity (like smoke).
These droplets are really good scatterers of visual light, so they appear white and solid to us in clouds, especially when far away. But take a plane ride, and you’ll see how (not solid?) clouds are.
When you say flat bottoms, you probably are talking about normal cumulus clouds or even cumulonimbus clouds (thunderstorms). They have flatter bottoms because these clouds form when air is unstable and rises up quickly (much like boiling water bubbles in a pot, this is called convection). As air rises, it cools and causes water vapor in the air to condense when the temperature cools to the dew point. The altitude at which this happens is called the lifted condensation level and it occurs at the same altitude on a given day in a given region (usually). So this level is like a boundsry where cloud begins to form in the upward moving air bubble, causing a stark, flat appearance.
Imagine a tiny speck of water, smaller than a drop and light enough to just float in the air. Now image 10 individual specks of water all floating separately. Now a hundred. A thousand. A million. A billion.
That’s how clouds work, they are not a solid lump of stuff like cotton candy but are just lots of absolutely tiny specks of water all floating separately.
The reason they can also be flat is because these specks of water can only exist and certain temperature/pressures. As you get lower in the atmosphere these change, so there is a certain height where the specks can’t exist any more.
BTW when conditions are right for clouds to exist at ground level, we call it fog.
Clouds aren’t actually “things” in the sky that like move and float around, what you are seeing is more like pockets of the atmosphere that have certain conditions. The air holds water, and when conditions change such that it can’t hold that much water you see clouds.
When you see they are flat on the bottom what you are actually seeing is the boundary layer of 2 layers of the atmosphere. One cold, one hot – one low pressure, one high pressure etc…
If you watch a time-lapse you can almost see that they are pockets of atmosphere coalescing moving like waves more than discreet objects.
I’ll let everybody else fight on the weight part, but I can handle the flat bottom part.
Water condenses out of the air due to temperature – at some altitude, the water vapor in the air becomes a cloud. Since air is usually layered by temperature, all the water at that altitude will convert from vapor to liquid at the same layer. That’s not always perfectly the case, of course, but a general rule.
So the first question is actually very simple – clouds are a combination of hot air, wind, and liquid water droplets. When water vapor condenses into liquid droplets, it releases heat into the surrounding air. Because of the hot air, they’re lower density enough to stay suspended, and the wind keeps the water droplets moving upward more than they fall.
And when they can’t stay suspended any more (due to the air getting less hot or the wind blowing downward instead of up or the droplets getting too big relative to the wind and hotness of the air), that’s when you get rain.
Clouds are flat because you have to reach a certain altitude before the water vapor can condense into droplets, and the transition between ‘unable to condense’ and ‘able to condense’ is usually a smooth line
I DONT KNOW BUT HERE’S MY BEST GUESS:
Imagine a person floating in the ocean.
It’s the same idea just with clouds floating in the sky.
Clouds are gases, and the air beneath is heavier, allowing them to stay in the air.
The water vapor from the air (basically cool steam) gets trapped in the clouds. When it gets too heavy, it rains.
I can’t believe how many wrong answers are being given here confidently. All solid objects are heavier than air. Clouds are made of either liquid or frozen solid water. They are always “heavier” than air. They are not held up by buoyancy. A cloud in the simplest sense can be modeled as a single very tiny drop of water. This drop is significantly denser than air. Yet it falls extremely slowly not because it’s buoyant but because of drag and updrafts. Have you never seen a dust mote in the sunlight ? Dust is much denser than air too. But like water droplets its “fall velocity” may be a cm per sec or less , too slow to see and easily offset by updrafts. A better explanation for clouds floating is not that they are floating but that they are being blown up into the air , much like an airplane, another object which seems to defy gravity.
If you’ve ever taken a hot shower, and seen all the steam in the room floating around you…times that by 1000 and voila.
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