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
Because while they are very heavy, they are very very big, giving them the low density needed to float. Just like how a massive cruise-liner can float in water even though they are similarly very heavy.
And rain happens when the tiny light droplets of water that make up the cloud start coalescing into bigger droplets, which are themselves denser than air, so they fall through the cloud, picking up more tiny droplets, letting them fall even more.
Clouds are ares where there is a high concentration of water vapour. As long as the water stays in a gaseous state, it’s lighter than air and will float. However, once you get enough water vapour into an area, it changes the thermal equilibrium and if any bits of high atmospheric dust disturbs the balance will cause the water vapour will freeze around the it. This makes it into little balls of ice which are heavier than air and thus will fall to the ground. Since the ice is moving from a bunch of atmosphere, it will melt into rain or transition into snow depending of the temperature as it falls.
It’s not really accurate to say that clouds are flat on the bottom? They are regions of water vapour concentration that don’t have defined 3d shapes and don’t have consistent concentrations throughout. That is why individual clouds look so different when we look at them from the ground.
“Judging by the amount of rain they must weigh a ton.”
Actually they likely weigh much more than that. Estimates are that the average cumulus cloud weighs over a million pounds.
But like the previous posters said, they are also very large so their density is low. Air has different densities depending on temperature and humidity, so it is common for certain altitudes to have clouds that could not exist at a different altitude. This density difference is also why they sometimes have flat bottoms, as they are against a layer of air with different temperature/density.
The air above the ground gets cooler as you get higher in altitude. It also gets less dense aka less atmospheric pressure. Clouds can only “float” at certain heights closer to the ground before becoming too dense and losing particles that eventually fall further and turn into rain and fall towards the ground.
Hot air rises and basically pushes on the base of the cloud upwards. That affects the shape you see from underneath the cloud. That’s also why clouds look all puffy on top. The air reaches its highest point before cooling down and falling back down to the ground again. This also creates the effect of the base of the cloud having humps because the air above the base falls faster than the warmer air beneath it can rise and pushes the base of the cloud downwards to create those bumps or humps.
Your main logical failing here is considering the weight of the cloud but dismissing the weight of the atmosphere.
If you pour oil on a pool of water, how does the oil float on the water, it’s heavy! Well the water is denser.
Dry air is denser than water vapour/humid/hot air. And that is why it floats above the ground (but not always, fog is a thing).
The reason that they are flat at the bottom, is that the water condenses out of the air at a given temperature based on the humidity (dew point). As you go up, the temperature drops, so at the height were the temp had dropped to the dew point, is where the clouds are. And since that’s a pretty sharp line, the clouds are flat at the bottom.
A lot of these answers mention that clouds are big, but I think they’re failing to properly explain that. Clouds are *huge*. Many visible clouds are routinely bigger than entire cities, and can cover multiple square miles and be hundreds or thousands of feet tall. Yes there’s a lot of water up there that weighs a lot, but it’s *very* spread out, over potentially millions of cubic feet in a single cloud. The density stays relatively low, despite getting enough vapor and crystals to see. Much like fog at ground level, in the right temperature and atmosphere conditions, visible water vapor and tiny droplets can stay suspended for a very very long time without falling.
Clouds form because warm moist air rises. The positive thermal buoyancy overcomes the negative bouyancy of the water vapor. Once that air reaches a certain height the water vapor condenses. As long as you have enough thermal buoyancy that cloud stays in the air.
Clouds aren’t any heavier than air. If you take air at the surface and cool it down, you start forming water droplets. No mass is added or removed – the moist warm air and cold air with suspended water droplets have the same weight. It’s basically a really misty day, but high up in the sky.
As air rises, it expands and cools, meaning that it can hold less water (it’s relative humidity increases). The ‘flat bottom’ is basically the point where the temperature is cold enough for the air to hit 100% humidity and invisible water vapor start condensing into visible droplets. It’s the equivalent of the dew point here on the ground.
You don’t immediately get rain because if the droplet falls, it hits warmer air and evaporate – never making it to the ground. If there is wind, that can also keep the water droplets in the air.
There are multiple things that can cause rain. The simplest and most relevant to your question is that the clouds moved to an area with colder air. The cold air hold less water, causing more droplets to form. If the air below is also cold, there’s minimal evaporation and the water hit the ground.
So clouds are actually the visible tops of much larger mountains of moisture. The line on the bottom is where the air gets too cool to hold it all in a gaseous state – so everything above that is visible.
They are very heavy but they’re relatively light compared to their enormous size. They’re comprised of water vapor which isn’t very dense. Rain forms through various factors but on a basic level droplets form when there’s particles for nucleation, that is solid particles like dust or dirt on which the water can condense back into a liquid.
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