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Name: Kyler
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Question:
How much do clouds weigh?


Replies:
Kyler,

Clouds can have a large range of mass per volume, depending on how large and numerous the cloud droplets or ice crystals are that are in them. However, they do not really weigh anything, if by weighing you mean putting them on a scale to weigh. Weight is defined as the force of an object upwards as the result of gravity. Since clouds, in a sense, defy gravity, they do not have weight.

Clouds are less dense than dry air of the same volume. That is why they do not fall from the sky. Upwards vertical motions in the atmosphere also help to counteract the weight of the droplets or ice crystals, helping to hold them up (or make them rise even) in the atmosphere.

You can learn more about cloud mass and composition at the USGS page at

http://ga.water.usgs.gov/edu/watercycleatmosphere.html

David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory


Kyle -

Clouds weigh a lot. Although they do not weigh as much as air. That is why they are usually buoyant - they float up high in the air because they are less dense than air. What is interesting is that wet (humid, that is) air weigh less than dry air. Because we are used to thinking of water as a liquid and air as a gas this does not seem to make sense. However, when you change water from a liquid to a gas (water vapor or steam) it is less dense than the air it replaces.

Saying that clouds weigh a lot also seems strange because we are used to thinking of air as very light. It is that way because we have always lived in the "sea" of air. If you drive along in your car at 60 miles per hour and hold your hand out the window - pushing the air out of the way - you realize that the air is quite heavy.

Have you ever flown in an airplane and felt the bumps in the air? That is air moving and it is massive enough to move even a heavy airplane. That rising air could eventually form a cloud (a cumulus cloud, that is) and some of those clouds make big bumps for the airplanes... but that is another story.

People say, "Light as air." But they are wrong.

Larry Krengel


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