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Q & A: Why does water vapor condense in clouds?

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Most recent answer: 06/14/2015
Q:
The sun heats the waters and eveporation takes place, the vapour rises. On reaching condensation level it condenses and come back as rain. Why why vapour condenses yet it's moving nearer to the heater(sun)??
- sadiki rungo (age 19)
democrtic republic of congo
A:

Nice question. Yes, the heat is coming from the Sun, but not directly. The main place the water gets heat is down at the Earth's surface, not up in the sky. Much of the upper atmosphere is quite cold because sunlight passes through it without getting absorbed much. When the sunlight hits the ground or oceans, it is mostly absorbed. So the ground gets hot, and water evaporates.  When the vapor goes up it reaches colder parts of the atmosphere and condenses. 

On a side note, as we change the atmosphere by emitting CO2, it gets harder for heat to flow as infrared light from the ground upward. As the Earth's surface gets hotter, some of the upper atmosphere gets cooler because of that reduced heat flow.

Mike W.


(published on 06/14/2015)

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