# Thermodynamics of Clouds

**URL:** <https://boards.straightdope.com/t/thermodynamics-of-clouds/454170>\
**Category:** Factual Questions\
**Created:** [June 25, 2008, 5:45am UTC](https://boards.straightdope.com/t/thermodynamics-of-clouds/454170 "2008-06-25T05:45:59Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\
**Post date:** [June 25, 2008, 5:45am UTC](https://boards.straightdope.com/t/thermodynamics-of-clouds/454170/1 "2008-06-25T05:45:59Z")

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I was outside on a sunny day, watching the clouds. I began to wonder why the clouds were relatively stable. At the Earth’s surface, the Sun’s light is about 1000 watts per square meter, which is a substantial amount of energy. A cloud is going to absorb a good part of that, and reflect the rest. I would expect the cloud to heat up and climb in altitude, or perhaps just dissipate into invisible water vapor. Since neither of those things appear to be happening, what happens to the energy? It has to go somewhere.

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**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\
**Post date:** [June 25, 2008, 12:58pm UTC](https://boards.straightdope.com/t/thermodynamics-of-clouds/454170/2 "2008-06-25T12:58:05Z")

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My WAG is that water has a lot of thermal equilibrium, and hence, containing tons and tons of water vapor, it will take some time before it evaporates (but evaporating is indeed its ultimate fate). Find one of those time-lapsed videos of clouds (I believe Youtube has some).

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**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\
**Post date:** [June 25, 2008, 1:03pm UTC](https://boards.straightdope.com/t/thermodynamics-of-clouds/454170/3 "2008-06-25T13:03:10Z")

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Why do clouds stay together? is it electrostatic attraction? One would think they would dissipate

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**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\
**Post date:** [June 25, 2008, 3:42pm UTC](https://boards.straightdope.com/t/thermodynamics-of-clouds/454170/4 "2008-06-25T15:42:44Z")

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\>Why do clouds stay together? is it electrostatic attraction? One would think they would dissipate

I think they dissipate by diffusion and by being stirred by wind shear, but an object so large would take a very long time for diffusion to dismantle, and the wind shear usually isn’t there. Clouds are regions of what we otherwise call fog, and don’t have any intrinsic strength.

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**Author:** ![Vlad\_Igor](https://avatars.discourse-cdn.com/v4/letter/v/7feea3/32.png) [@Vlad\_Igor](https://boards.straightdope.com/u/Vlad_Igor)\
**Post date:** [June 25, 2008, 5:16pm UTC](https://boards.straightdope.com/t/thermodynamics-of-clouds/454170/5 "2008-06-25T17:16:22Z")

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Clouds are the result of a parcel of air in surrounding air with a temperature below the parcel’s dewpoint. The parcel of air can be from the ground (its buoyancy is determined by how much it is heated by the ground and how rapidly the surrounding air cools as the parcel rises), or it can be from moisture carried in by a jet stream. Cumulus clouds are the result of ground heating a parcel of air causing to rise, so those clouds delineate a mass of air. OTOH, stratus clouds are the result of moist air carried along by a jet stream, and represent a broad layer of air.

Vlad/Igor