|WHY DOESN'T GRAVITY PUSH CLOUDS|
TO THE GROUND?
METEOROLOGIST JEFF HABY
Clouds represent air that has risen and condensed water vapor into cloud droplets. Air rises when the upward
directed pressure gradient force is greater than the force of
gravity. An increase in the upward directed
pressure gradient force can occur when the air is positively buoyant or when the air has been
forced to rise.
Clouds tend to contain more
moisture than the air surrounding the cloud.
Water vapor is much lighter than
diatomic Nitrogen or diatomic Oxygen. Since water vapor is less dense than
dry air, moist air will have
a tendency to float above drier air (all else being equal). Clouds float on drier air just as bubbles
float on water.
The cloud droplets that make up a cloud are very tiny. Air movements have much more of an effect on moving
cloud droplets as compared to gravity. Compare dropping a feather to that of dropping a baseball. The
baseball will quickly fall to the ground while the feather will gradually flutter to the surface. Now
compare a feather to a dust particle. The dust particle will take longer than the feather to reach the
surface since even the slightest movement of air will keep the dust particle suspended.
Clouds do not have a tendency to sink since they are less dense than the air below or around them. Clouds
that do sink will eventually evaporate since the sinking process produces a warming of the air.
Warmer air can evaporate more moisture than colder air.