Because the altitude at which air reaches its dew point is fairly constant in a given situation, clouds often have pretty flat bottoms, all of which line up; the illusion created is that the clouds are sitting on some sort of invisible surface. (In reality, rising air is rising through a sort of boundary line where cloud drops begin growing rapidly.)
The next time you see light, fluffy cumulus clouds apparently floating in the sky, imagine air rising where the cloud is, and sinking in between, continuously creating the appearance you see.
Cumulus mediocris and congestus over Swifts Creek, Australia (Wikipedia Commons)
Galapagos, Tortuga Bay (Wikipedia Commons)
Make your own cloud! Take the label off a soda bottle (the bigger the better) so you can see inside more conveniently. Get a match ready to light. Put a little water (a tablespoon or two is enough) into the bottle and shake it. Now light the match, let it burn a moment, then blow it out and drop it, still smoking, into the bottle. Put your mouth to the open end of the bottle and blow, increasing the air pressure in the bottle. After a few seconds--and while watching what is happening inside the bottle--release the air. There: do you see it? The air went cloudy the moment you released the pressure. Clouds you make this way will sometimes last several minutes.
Let's see how that energy can be a powerhouse. The sun warms moist ground or a lake, causing water to evaporate and form a warm and humid body of air. The warm moist air begins to float upward in the cooler air around it because warm moist air is lower in density. As it rises, the drop in pressure causes that body of air to expand, lowering its temperature below the dew point. If this warm air were dry, it would cool enough to be the same temperature as the cooler air around it, its density would match that of the surrounding air, and it would stop rising--end of story. BUT because that air is humid, water vapor begins to condense into cloud drops. The process of condensation produces heat (that potential energy is no longer just potential!) that prevents the air from cooling any further, so it continues to rise. Condensation continues in the rising air, causing the cloud to tower higher and higher, until the supply of water vapor is small enough that condensation ceases, the air stops rising, and the cloud stops building. If there is enough water vapor to build the cloud into a thunderhead, a thunderstorm may result. And if there is enough warm, humid air (say, over the subtropical Atlantic Ocean in summer) then the energy of the condensing water vapor may power a hurricane--a kind of runaway freight train of condensation--and the most destructive of all storms.
More coming about particular clouds...
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