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!
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!
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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