Not an expert but I would think the water vapor that doesn’t fall as rain just evaporates faster than it “spreads out”. But then again you could make the argument that this is in reality spreading the cloud out so thinly and evenly that you can see right through it
Given enough time, eventually it will cause everything to spread out evenly leading to the heat death of the universe.
However, the Earth’s atmospheric conditions are (relatively) small scale events happening in a (relatively) small amount of time. The Sun and the Earth are adding a large amount of energy into the atmosphere in an uneven fashion, which means entropy doesn’t have a chance to settle everything.
Since the sun is constantly heating Earth unevenly, the atmosphere is always going to be out of balance somewhere. Another part of the answer comes down to how clouds generally form in the first place. Most clouds form because one mechanism or another causes air to rise and cool. If there is enough moisture in the air, it can condense into liquid droplets (or freeze into ice crystals) and form a cloud. If enough moisture condenses or freezes, it falls as rain or snow. But if air is rising in one place, it must be sinking somewhere else. This has the opposite effect: air warms up as it sinks, which tends to make clouds evaporate. On your stereotypical summer day with puffy white cumulus clouds, air inside the clouds is rising while air in between them is sinking.
A lot of times the air at higher altitude is pretty dry, so clouds will evaporate as dry air gets mixed in.
It’s the same thing that causes the unique atom bomb mushroom cloud shape.
You add humidity to Air and it becomes lighter. It rises leaving a little pressure behind into which dryer air flows. If there’s a moisture source for that dryer air to absorb moisture from it will also become more humid and begin to rise.
One of the things you’ll notice about clouds is that they usually have a flat bottom if it’s not a general overcast. That is the point where the rising column of air enters a range of sufficiently low pressure and sufficiently low temperature to begin condensing water into droplets.
So the water vapor becomes a mist which we see as clouds. Any of that missed falls below that line it tends to re-evaporate.
Meanwhile the total amount of heat released from the latent heat of condensation causes the cloud to become much warmer which spreads out the molecules and again keeps the volume of air lighter and rising. The updraft continues to provide a low pressure that draws in air from the sides.
So like any form of convection the volume of air wants to rise not spread out. The denser air near it acts as a container of sorts.
Technically, that’s what everything is attempting to do, which is where the weather comes from. Low pressure meets high pressure, Dry meets wet. Hot meets cold. The more organized these systems are the more wild it gets
“Organized” is low entropy. Organized atmospheric conditions want to equalize.
I feel like the answers don’t address the question: why does vapor cluster into dense clouds instead of dissipating?
The key lies in how and where condensation occurs. Water vapor condenses into droplets only under specific conditions, when moist air rises, cools at higher altitudes and reaches its dew point. This happens in localized regions of the atmosphere where pressure and temperature are just right. So the cloud is momentarily stabilized by these conditions (temperature, pressure) that force moist air to form water droplets. The ever changing pressure and temperature conditions, for example warm air hitting a cloud can cause it to evaporate again.
Entropy is confusing here because the idea of increasing entropy applies to closed systems which means that temperature and pressure can become consistent, eliminating all gradients or local differences and any weather patterns. But the global weather system is very much not closed, as many people have pointed out, and so local conditions (pressure, temperature, moisture) vary dynamically as layers of local conditions keep mixing, preserving gradients and change etc. indefinitely.
Think of it like filling a tub. Physics says that the water level in the tub should be level, yet there are all kinds of turbulence and even water hills in there. The same when draining one, and even when filling while the drain is open.
The same is happening with entropy and the Earth. The sun is filling it with highly ordered energy on one side, it swirls around a while, then is drained into space as way less ordered energy. That flow is now also having all kinds of turbulence and hills of high order.
Cloud patterns are a pretty immediate one, but even the entropy-defying nice order of letters in this comment is caused by the turbulence of order washing over the Earth.
Comments
Because we have the Sun. Entropy increases in closed systems. If energy comes in, you can get things that have less entropy.
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Not an expert but I would think the water vapor that doesn’t fall as rain just evaporates faster than it “spreads out”. But then again you could make the argument that this is in reality spreading the cloud out so thinly and evenly that you can see right through it
Given enough time, eventually it will cause everything to spread out evenly leading to the heat death of the universe.
However, the Earth’s atmospheric conditions are (relatively) small scale events happening in a (relatively) small amount of time. The Sun and the Earth are adding a large amount of energy into the atmosphere in an uneven fashion, which means entropy doesn’t have a chance to settle everything.
Since the sun is constantly heating Earth unevenly, the atmosphere is always going to be out of balance somewhere. Another part of the answer comes down to how clouds generally form in the first place. Most clouds form because one mechanism or another causes air to rise and cool. If there is enough moisture in the air, it can condense into liquid droplets (or freeze into ice crystals) and form a cloud. If enough moisture condenses or freezes, it falls as rain or snow. But if air is rising in one place, it must be sinking somewhere else. This has the opposite effect: air warms up as it sinks, which tends to make clouds evaporate. On your stereotypical summer day with puffy white cumulus clouds, air inside the clouds is rising while air in between them is sinking.
A lot of times the air at higher altitude is pretty dry, so clouds will evaporate as dry air gets mixed in.
It does, over the full time scale of thee cosmos
That would be because of updrafts.
It’s the same thing that causes the unique atom bomb mushroom cloud shape.
You add humidity to Air and it becomes lighter. It rises leaving a little pressure behind into which dryer air flows. If there’s a moisture source for that dryer air to absorb moisture from it will also become more humid and begin to rise.
One of the things you’ll notice about clouds is that they usually have a flat bottom if it’s not a general overcast. That is the point where the rising column of air enters a range of sufficiently low pressure and sufficiently low temperature to begin condensing water into droplets.
So the water vapor becomes a mist which we see as clouds. Any of that missed falls below that line it tends to re-evaporate.
Meanwhile the total amount of heat released from the latent heat of condensation causes the cloud to become much warmer which spreads out the molecules and again keeps the volume of air lighter and rising. The updraft continues to provide a low pressure that draws in air from the sides.
So like any form of convection the volume of air wants to rise not spread out. The denser air near it acts as a container of sorts.
It does, but you have to wait a few more billion years
Technically, that’s what everything is attempting to do, which is where the weather comes from. Low pressure meets high pressure, Dry meets wet. Hot meets cold. The more organized these systems are the more wild it gets
“Organized” is low entropy. Organized atmospheric conditions want to equalize.
I feel like the answers don’t address the question: why does vapor cluster into dense clouds instead of dissipating?
The key lies in how and where condensation occurs. Water vapor condenses into droplets only under specific conditions, when moist air rises, cools at higher altitudes and reaches its dew point. This happens in localized regions of the atmosphere where pressure and temperature are just right. So the cloud is momentarily stabilized by these conditions (temperature, pressure) that force moist air to form water droplets. The ever changing pressure and temperature conditions, for example warm air hitting a cloud can cause it to evaporate again.
Entropy is confusing here because the idea of increasing entropy applies to closed systems which means that temperature and pressure can become consistent, eliminating all gradients or local differences and any weather patterns. But the global weather system is very much not closed, as many people have pointed out, and so local conditions (pressure, temperature, moisture) vary dynamically as layers of local conditions keep mixing, preserving gradients and change etc. indefinitely.
Think of it like filling a tub. Physics says that the water level in the tub should be level, yet there are all kinds of turbulence and even water hills in there. The same when draining one, and even when filling while the drain is open.
The same is happening with entropy and the Earth. The sun is filling it with highly ordered energy on one side, it swirls around a while, then is drained into space as way less ordered energy. That flow is now also having all kinds of turbulence and hills of high order.
Cloud patterns are a pretty immediate one, but even the entropy-defying nice order of letters in this comment is caused by the turbulence of order washing over the Earth.