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Why do clouds stick together?





ocalhoun
I noticed while flying (and it is indeed a groundbreaking discovery) that clouds stick together in clumps, usually.

The sky will often be a bunch of isolated clumps of cloud within a wide expanse of areas with no clouds.

This seems at odds with what I know of entropy though. I'm told that things tend to move from areas of high concentration to areas of low concentration...
But clouds don't seem to follow this rule at all.

So, I'm wondering, what physical force causes the attraction that keeps clouds from dissipating (most of the time)?
kelseymh
ocalhoun wrote:
I noticed while flying (and it is indeed a groundbreaking discovery) that clouds stick together in clumps, usually.

The sky will often be a bunch of isolated clumps of cloud within a wide expanse of areas with no clouds.

This seems at odds with what I know of entropy though. I'm told that things tend to move from areas of high concentration to areas of low concentration...
But clouds don't seem to follow this rule at all.

So, I'm wondering, what physical force causes the attraction that keeps clouds from dissipating (most of the time)?


Generally air pressure differences or temperature gradients. Think about, for example, thermohaline levels in the ocean. You're right to think about this in thermodynamic terms! A pressure or temperature difference means that the system is <b>out of thermal equilibrium</b>, and that non-equilibrium means that work can be done to organize or separate parts of the system.

Take a look at the Wikipedia discussion: http://en.wikipedia.org/wiki/Cloud#Formation:_how_the_air_becomes_saturated, http://en.wikipedia.org/wiki/Cloud#Cohesion_and_dissolution.
stanloplato
Quote:
Clouds do not stick together at all. Clouds are formed by micron sized droplets of water. They appear to stick together because the temperature-humidity characteristics of the atmosphere in the locality of the cloud is right for the droplets (cloud) to form.

The cloud appears white because the micron sized water droplets scatter light by a process called Mie scattering.

If you want to see clouds form and disperse just take an hour or so on a nice sunny, partly cloudy day and lie on the ground and do nothing more than look at the clouds come into existence and slowly dissipate.


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- Ankhanu
sanahwinari
i think it because the winds
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