Ask Ellen: Why do some clouds have flat bottoms and puffy tops?

Ask Ellen

GRAND RAPIDS, Mich. (WOOD) — After last week’s gorgeous weather, Storm Team 8 had several people ask, “why do some clouds have flat bottoms and puffy tops?”

The only clouds that do this are cumulus clouds. They are the only clouds in the atmosphere that are driven by convection. They begin when the sun heats the ground or a sharp boundary forces air upward in a layer.

Cumulus clouds are often noted for their puffy, white appearance, and unlike flat stratus clouds, they can form little turrets of convection that look like the tops of cauliflower.

So, what causes the flat base of a cumulus cloud and the puffy cauliflower tops? It starts with the sun.

As the sun shines over the earth, it sends solar radiation into our atmosphere. This sunshine heats the ground. Once the ground begins to warm, it releases its heat back into the air directly above it, creating a layer of warm air close to the surface.

We know warm air rises because it is less dense. So, this layer of warm air begins to rise.

As the layer of warm air ascends, it gets further from the ground and starts to cool. The dew point in the air layer, however, stays exactly the same. Eventually this layer of warm air will hit a very important threshold — the elevation where the temperature has now cooled off to be exactly the same as the dew point in the layer.

This is called the Lifting Condensation Level. It’s the level of saturation where clouds become visible. This is why all the cumulus clouds seem to start at the same point.

As the clouds continue to grow, the air in the cloud expands as the air pressure drops at roughly one inch per 1,000 feet. Some pockets will grow upwards more than others, which is why these same clouds look puffy on top!

Look for more of these cumulus clouds year round! And send your questions to The7on8@woodtv.com!

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