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Why aren't clouds on the ground?

  1. Jun 24, 2012 #1
    What forces keep clouds up in the sky?

    It seems to me that they are somewhat close to the ground but yet they always hang at about the same altitude. It looks like they are being held up by something on the bottom since the bottoms of the clouds are flat. But they don't spill out all over that "ceiling" either.
  2. jcsd
  3. Jun 24, 2012 #2


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    Clouds exist at various altitudes and can sometimes be characterized by those altitudes. Cirrus clouds are generally very high in the sky for instance.
  4. Jun 24, 2012 #3


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    Fog is a cloud.
  5. Jun 24, 2012 #4
    That's debatable. Meteorologist don't consider fog to be clouds.

    And clouds do 'fall'. The tiny droplets are just subject to gravity. However the rate of falling is minute, like dust that settles slowly. Most of the time clouds are formed due to the (adiabatic) cooling of air parcels that are lifting up due to several different causes (convection advection, hill side), and this uplift also keeps those droplets up for a longer time. Droplets that do fall out of the clouds, get in warmer air and usually evaporate again. This happens generally at the same altitude and that is one of the reasons that the base of most clouds is flat. The other reason is that in the updraft the cooling air reaches the dewpoint.

    If for some reason the uplift of air stops, all droplets fall down and evaporize; the cloud disappears.

    Last edited: Jun 24, 2012
  6. Jun 24, 2012 #5
    I'll debate it:

    This is saying that when a cloud is on the ground we change its name to fog, and therefore, clouds don't exist on the ground. Hehe.
  7. Jun 24, 2012 #6


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    The OP's question is not being addressed. The OP is under the misapprehension that clouds are being "held up", like they're sitting on an invisible surface.

    I don't have the eloquence to answer it succinctly.
  8. Jun 24, 2012 #7


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    Clouds form wherever there is more water in the air than it can readily hold as a gas. If there is a lot more water than the ait can hold, then it DOES fall back to earth. Of course, it may also evaporate again before reaching the ground.
  9. Jun 24, 2012 #8
  10. Jul 5, 2012 #9
    Its all about condensation and yes clouds can be on the ground.

    I've been a skydiver for over 30 years and the why and what of clouds is a question I've had from childhood. There are some insightful comments here about dew point and it all has to do with water in a gas solution and condensation. Air can hold a considerable amount of moisture. As pressure and temperature drop water comes out of solution and begins to form micro droplets, generally around dust particles.

    Clouds can form at pressures and temperatures starting at sea level. This happens when dew point conditions (pressure vs temp) are present at ground level. This is called fog. You could also find yourself in a Mountain community and have clouds blow your way and find yourself in a fog but generally the warmer Earth will help lift the cloud bottoms or cloud base above you.

    Why some clouds form a flat bottom is due to this "dew point", air pressure will be pretty uniform at a given altitude and temperature also follows closely. In skydiving dew point is a cheap mans altimeter, if the cloud base is at 3,500 feet on the plane ride up it will likely be there on the fall back down and a good visual reference for a known altitude.

    On a foggy morning you can watch the dew point lift as the Earth warms and by mid morning that dew point may be 2000 feet or more overhead. Also you can watch as thermals lift air past the dew point and watch as water comes out of gas solution, its quite amazing. Its all about condensation caused by temperature and pressure.
    Last edited: Jul 6, 2012
  11. Jul 6, 2012 #10
  12. Jul 6, 2012 #11
    Thanks at least I'm consistent when I make a spelling error.
  13. Jul 6, 2012 #12
    Yea right Dave, you just didn't try :smile: Your posts often meet those qualities on much more complex topics.

    I immediately thought of "buoyancy". In particular because of relative pressures partly determining where and altitude of clouds.

    Fog is too heavy (dense) to be a cloud isn't it?
  14. Jul 6, 2012 #13
    Well as I said before: clouds do fall, however..

    Last edited: Jul 6, 2012
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