Why aren't clouds on the ground?

*vampares*

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.

turbo

Clouds exist at various altitudes and can sometimes be characterized by those altitudes. Cirrus clouds are generally very high in the sky for instance.

Hurkyl

Fog is a cloud.

Andre

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.

more

zoobyshoe

Quote by Andre

That's debatable. Meteorologist don't consider fog to be clouds.

I'll debate it:

Fog is a collection of liquid water droplets or ice crystals suspended in the air at or near the Earth's surface.[1] While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes).

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.

*DaveC426913*

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.

russ_watters

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.

zoobyshoe

Quote by DaveC426913

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.

Clouds and fog form when the temperature of the air reaches the condensation point, which is the point at which water vapor (which is an invisible gas) becomes a liquid. When it reaches this point, the liquid collects on the dust particles in the air and become visible.

We call the results clouds, unless the clouds form at the ground surface, in which case we call it fog. Various factors influence the exact point at which condensation can occur, such as the air pressure at a given altitude, the moisture content of the air, and the air temperature. In most cases, air temperature is the most important factor.

As we know, temperature typically doesn't vary dramatically in the horizontal, but temperature does vary with height. In fact, temperature typically decreases with height, as can be found when climbing a mountain. This fact means that the condensation point is also horizontally uniform at a given altitude. Above this altitude, water vapor will condense out to form clouds, below it water will remain in its gaseous state. Therefore, because the point at which condensation occurs tends to be about as uniform as surface temperature, the bottoms of most clouds will appear flat.

Even though the condensation point tends to be at a constant altitude, the cloud will continue to grow vertically after condensation. How high it will grow depends again on the three factors discussed above. However, as the cloud grows vertically, it will draw in drier air from the surrounding atmosphere. The cloud will then start to evaporate along the edges and erode, leading to the "fluffy" look.

Not all clouds, however, have a rounded, fluffy appearance on top. Those that do are called cumulus clouds. They are formed as warm, moist air rises and cools to the condensation point. The air stops rising when it cools to the temperature of the surrounding air in the atmosphere. In contrast, stratus clouds form when the ambient temperature of the air reaches the condensation point by being forced aloft, such as over a warm frontal boundary. There is little vertical motion of the air, so the clouds form in place and have a flat bottom AND top. Both types have "flat" bottoms though, formed through the process discussed above.

http://www.wrh.noaa.gov/fgz/science/...ud.php?wfo=fgz

Sky Junky

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.

Andre

Quote by Sky Junky

"due point".

Dew point

Sky Junky

Quote by Andre

Dew point

Thanks at least I'm consistent when I make a spelling error.

nitsuj

Quote by DaveC426913

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.

Yea right Dave, you just didn't try

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?

Andre

Quote by nitsuj

Yea right Dave, you just didn't try

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?

Well as I said before: clouds do fall, however..

They remain aloft as long as the drag force of the air dominates over the gravitational force for small particles. If the cloud droplets continue to grow past this size, they become too heavy to be held aloft as the gravitational force overcomes the atmospheric drag, and they fall from the cloud as rain

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vampares	Why aren't clouds on the ground? 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.

turbo Recognitions: Gold Member	Clouds exist at various altitudes and can sometimes be characterized by those altitudes. Cirrus clouds are generally very high in the sky for instance.

Hurkyl Recognitions: Gold Member Science Advisor Staff Emeritus	Fog is a cloud.

DaveC426913	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.

russ_watters Mentor	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.