Why are clouds so often flat on the bottom but puffy on top?

Answer 1

where you see that the cloud is flat on the bottom thats where the "dew point" is. (you know how you wake up and the grass is wet and such, thats cause the dew point was at ground level during the night) so when convection occurs (warm air rising) it hits the dew point and forms a cloud, thats why the bases of clouds are flat. they are puffy on top because as long as theres an updraft (due to convection) traveling up into the cloud, the clough will keep growing. The cloud can become large and become so large that it can get flat on top due to the strong winds in the atmosphere. These are always most likely cumulonimbus clouds (thunder clouds.storms) these clouds get whats known as a "anvil top"
here are some pics:
http://www.ece.fr/~rozanc/foudre/images/photos/imagepages/image6.html
http://scijinks.jpl.nasa.gov/en/educators/gallery/clouds_atmos/cumulonimbus_L.jpg

there can also be clouds with puffy bottoms too! they're called mammutus clouds, and these are caused by down drafts from the within the cloud, also in a cumulonimbus cloud, up draafts in one end and down drafts out of the other end
http://www.icstars.com/Ranch/Douglas/clouds.html

hope this information helps you and makes sense =p =)

Answer 2

Cloud Bases

Why clouds have different looks to their bases, where many clouds have flat bottoms and others have jagged or bumpy bases.

It starts with clouds formation. Clouds begin as rising warm, moist bubbles of air that run into a cold shield of air sitting aloft. Eventually, these pockets of air will hit a point where the temperature is too cold to hold the water as a vapor. The air bubble has no choice but to condense its water vapor into a cloud made of very small water drops.

When this process occurs at different heights, the cloud takes on a ragged or lumpy appearance on its underbelly. If the condensation of the air bubbles occur at nearly the same height for all of them, the cloud will form a flat base.

Strong wind will also shape a cloud. Moderately strong winds near the base of a forming cloud will mix up the air near the base, making the area pretty uniform in temperature and moisture. The end result is a flatter looking base.

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Another explination:

Before we look at why clouds are flat on the bottom, a little review on how clouds form, or exactly what a cloud is, might be helpful.

Clouds are condensed water vapor in the atmosphere, either in a liquid, or solid form. (Yes, some clouds are composed of tiny ice crystals, and thesemare called "cirrus" clouds. They are very high in the atmosphere (above 20,000 feet), and they are the wispy, feathery-looking clouds in the sky.
Their bases are not flat, but may appear that way, because they are so high, or far away from us.

The other kind of clouds, the ones composed from liquid water droplets, form in a variety of ways, but the end result is air containing water vapor is cooled to its saturation point, and then the water vapor condenses into visible water droplets, called clouds. When air rises, it cools, and at a particular level, it reaches its saturation point, and clouds form. That level constitutes the bottom, or base of the cloud. (This level depends on a variety of conditions, including temperature, air pressure, amount of moisture in the air, etc.) But the height of the cloud bases over a given area is fairly uniform, and the bases appear to be flat.

Here is a website that discusses cloud formation:
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/home.rxml

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Another explination:

Sometimes clouds aren't flat on the bottom, although they usually are.

As air rises, it cools until it gets down to the temperature at which the relative humidity is 100%. At that point water vapor forms droplets on particles; sometimes the particles are soil, or they could be particulate air pollutants. Since large parcels of air (cumulous clouds) or the entire layer of air (stratus clouds) is rising at the same time and at the same rate, the water droplets form at the same height, giving a fairly flat
bottom to most clouds.

There are exceptions to the flat bottom. Sometimes the droplets become too heavy to be suspended by the upward rising air; then they may slowly fall out of the cloud in bands (called virga) or bulbous shapes (such as the mammata cloud forms under the anvil of a thunderstorm) which appear under the cloud. Technically, these droplet fallouts could be called precipitation, but meteorologists still think of them as part of the cloud.

Answer 3

Temperature drops with altitude (thinner air = less pressure = less heat)

When temperature drops to "dew point" water in the air condenses and clouds form.

The humidity in the air is fluctuates widely. That is, there are cells with lots of humidity.

All the cells of high humidity will condense at the same altitude (actually the same dew point) and thus the cloud bases are all seen at that altitude.

Answer 4

usually an optical illusion. it looks flat when you look upwards at them but the bottoms still have dips and rises in them. It would take a strong bottom shear wind to make them nearly flat. the tops are in warmer air so the top rises as they hold more moisture giving the top a rounded look.

Answer 5

Different layers in the atmosphere.

When a cloud becomes too dense for the current 'layer' but not dense enought to move to the lower layer, it gets 'squished' on the 'floor' of the layer, giving it a flat bottom.

Answer 6

Due to astmospheric pressure & tempereture affecting the density of the clouds...

Answer 7

the density of the cloud and the air temp in the atmosphere

Answer 8

i think because the difference in their altitudes.

the bottom part is subjected to gusty winds so it flattens while the top is not