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Why does not all rising air form clouds?
Question Date: 2015-04-06
Answer 1:

Very nice question! Rising air is a mixture of several gasses. The most abundant are N2 at 78%, O2 at 21% and depending on the humidity H2O, which can vary from 0% (VERY DRY DESERT AIR) to 4 % (moist tropical environment).

Now, when air that has some H2O gas in it rises, the air will cool because as it rises the gas expands since the pressure is less. Now when this air rises and cools due to expansion, at some point (altitude) the temperature falls low enough so that, the water vapor that is present will condense to form tiny, tiny droplets of liquid water. Remember when a gas cools it will condense to form a liquid. So if we have some air at the surface that contains say 1% H2O gas, as it ascends and cools, the temperature will be (at some altitude above the Earth’s surface) such that H2O gas is not stable, but instead H2O liquid IS stable: A CLOUD FORMS!!!!!

The height above the land (altitude) where a cloud forms depends on the starting temperature at surface and the % percentage of H2O gas or H2O vapor in the air!

Next time we have a beautiful blue sky day, look for small puffy cumulus clouds that form over the mountains, especially afternoon. These cumulus clouds seem to have a sharp base! That is because at exactly that height above the land, the temperature is exactly at the number needed to CONDENSE the water vapor to liquid water droplets, VERY TINY so they do not fall at an appreciable rate. Now, if this surface air was VERY, VERY DRY, it would not form a cloud until much greater heights. And if the air was dry, the rising air would NEVER FORM a cloud. If you know the humidity of the air at the surface, then you can use the height of the base of the cloud to predict what the temperature is there!

Answer 2:

For clouds to form the rising air must be supersaturated with moisture (water vapor). With no water vapor, clouds can't form. So it really depends on where this rising air comes from. If it's from a really dry area (like a desert), that air might not be carrying a lot of moisture, making it more difficult to form clouds. On the other hand, if the rising air is from the ocean (where there's plenty of water vapor), more clouds might form. I hope I answered your question. Good luck with your studies!

Answer 3:

Clouds form when the temperature of the air drops low enough for the water vapor contained in the air to no longer be able to exist as vapor. It condenses into liquid droplets or freezes into ice crystals - which are what clouds are made of. Air that is too warm already, or just too dry, won't be able to form clouds.

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