How Much Does A Cloud Weigh?

MyNameIsFred writes "ABC News is running an article revealing unexpected facts about weather formations. Ever wonder how much a cloud weighs? What about a hurricane? A meteorologist has done some estimates and the results might surprise you..." Reports that include the phrase "more than all the elephants on the planet" are always welcome.

An earlier answer

[staplegun]

Cecil Adams answered [straightdope.com] this a few years back. Sure he uses 747's instead of elephants, but his answer is a bit more detailed.

Don't you hate people who can't estimate?

[Anonymous Coward]

From the article "That means the water in one hurricane weighs more than all the elephants on the planet. Perhaps even more than all the elephants that have ever lived on the planet."

Assume an elephant generation is 50 years. Assume the average number of elephants in Africa at any one time is 100,000 (this will be way low historically). So, 40 million elephants are born in 400 generations, or only 20,000 years.

So there's no way this atatement "more than all the elephants that have ever lived on the planet" is correct.

When I was studying physics the lecturer was very insistent about us being able to do back of the envelope calculations - for example, how many photons does a 1.5 volt torch make on a full battery.

Cheers,
James

Why do clouds float?

[Aaron England]

Clouds are composed primarily of small water droplets and, if it's cold enough, ice crystals. The vast majority of clouds you see contain droplets and/or crystals that are too small to have any appreciable fall velocity. So the particles continue to float with the surrounding air. For an analogy closer to the ground, think of tiny dust particles that, when viewed against a shaft of sunlight, appear to float in the air. Indeed, the distance from the center of a typical water droplet to its edge--its radius--ranges from a few microns (thousandths of a millimeter) to a few tens of microns (ice crystals are often a bit larger). And the speed with which any object falls is related to its mass and surface area--which is why a feather falls more slowly than a pebble of the same weight. For particles that are roughly spherical, mass is proportional to the radius cubed (r3); the downward-facing surface area of such a particle is proportional to the radius squared (r2). Thus, as a tiny water droplet grows, its mass becomes more important than its shape and the droplet falls faster. Even a large droplet having a radius of 100 microns has a fall velocity of only about 27 centimeters per second (cm/s). And because ice crystals have more irregular shapes, their fall velocities are relatively smaller. Upward vertical motions, or updrafts, in the atmosphere also contribute to the floating appearance of clouds by offsetting the small fall velocities of their constituent particles. Clouds generally form, survive and grow in air that is moving upward. Rising air expands as the pressure on it decreases, and that expansion into thinner, high-altitude air causes cooling. Enough cooling eventually makes water vapor condense, which contributes to the survival and growth of the clouds. Stratiform clouds (those producing steady rain) typically form in an environment with widespread but weak upward motion (say, a few cm/s); convective clouds (those causing showers and thunderstorms) are associated with updrafts that exceed a few meters per second. In both cases, though, the atmospheric ascent is sufficient to negate the small fall velocities of cloud particles. Another way to illustrate the relative lightness of clouds is to compare the total mass of a cloud to the mass of the air in which it resides. Consider a hypothetical but typical small cloud at an altitude of 10,000 feet, comprising one cubic kilometer and having a liquid water content of 1.0 gram per cubic meter. The total mass of the cloud particles is about 1 million kilograms, which is roughly equivalent to the weight of 500 automobiles. But the total mass of the air in that same cubic kilometer is about 1 billion kilograms--1,000 times heavier than the liquid! So, even though typical clouds do contain a lot of water, this water is spread out for miles in the form of tiny water droplets or crystals, which are so small that the effect of gravity on them is negligible. Thus, from our vantage on the ground, clouds seem to float in the sky.

The Weight of A Flea

[driftingwalrus]

It took quite a lot of research, but I did find out how much a flea weighs. It is approximately one millionth of a pound, or .000001 pounds. So, 1 trillion times 1 millionth of a pound would be... 1,000,000 pounds! It's closer to weighing as much as one billion fleas.

The grammar nazi does not approve

[ls -lR]

<grammar nazi hat on>
Is that what professionial journalism has come to?

The thought of a hundred elephants-worth of water suspended in the sky begs another question -- what keeps it up there?

Why must people keep abusing the phrase, "begs the question?" [2blowhards.com] It does not mean "causes us to question" or "makes me wonder." Just because MANY people keep making the same mistake does not make it so.
</grammar nazo>

Re:Nonsense

[CyberDruid]

Of course the sky is blue. Look out your window and see for yourself. The sky is the cause of it's own blueness (by scattering those wavelengths better), thus it is truly blue.

Perhaps you are thinking of the sun? One could argue that it is not really yellow, since outside of our atmospheric filter it is actually white.

Getting up close and personal with those elephants

[Infensus]

Try skydiving trough a cloud. The do indeed look fluffy and soft from an airplane, but when you fall trough them at 200-280kmh, it feels quite different.. All those small droplets hitting your bare skin feels like hundreds or thousands of small nails, and larger drops can be be painful trough thin clothing as well..
Not to mention hail within clouds. Hail is really, really painful. Skydivers really don't like hail. At all.

Re:I am not a meteorologist

[Anonymous Coward]

That's correct. A hurricane is far less dense than a stormcloud, so there's less water per cubic metre.
There's a hell of a lot of energy in a hurricane though, which is also what causes it to expand to a very large, but less dense, size.

Re:NEWS ALERT (Summary)

[Anonymous Coward]

Sorry - I think it goes something like this:

Clouds are made of a lot of water. A lot of water has a lot of mass. Clouds have a lot of mass.

Being heavy and having a lot of mass are two different things - as I am sure you are aware.

I think, by definition, clouds are not heavy ( relatively speaking). If they were, they would not be able to be supported by air, they would be supported by the ground.

Re:Metric Metric Metric

[nn4l]

Never underestimate the size of one square meter.

One square meter has 10.000 square cm (100 cm * 100 cm).

Total area is 500 * 10.000 = 5.000.000 cm^2

Mass is 3 * 5.000.000 = 15.000.000 g, or 15.000 kg, or 15 (metric) tons.

About 2.5 elephants.

Clouds don't "weigh" anything

[Anonymous Coward]

If they did, they would fall out of the sky. They have a mass, but no weight. Weight is the measure of the downward force a mass exerts. That is why you don't weigh as much on the moon. You have the same mass, but less weight. Clouds float, so they are weightless. If clouds had weight, you would need skyhooks to keep them up in the air.

Wrong

[Anonymous Coward]

Six tonnes are 6,000 kg, six tons is something different.

Scientific American Website

[toofanx]

This is courtesy the Scientific American website [sciam.com]. There is more information out there.

Another - better - source

[neglige]

Seems like nobody mentioned this before. Here [noaa.gov] seems to be a better source for the answer.

Re:Clouds don't "weigh" anything

[ninthwave]

The do have weight because the have a downward force from the relation of their mass within the gravity of earth. But because of their low density they float in the air. Just like a feather has weight but still floats in the air currents.

All objects that have a mass have weight. Weight is related to the gravitational conditions the object is in. You are confusing weight and density / buoyancy.

Physics 101 please try this class again.

Re:NEWS ALERT (Summary)

[meta-monkey]

Extremely smarmy engineer answer:

<smarm>
Well, grass isn't actually green, per say. Nothing really IS a color, it's just that grass happens to absorb all the wavelengths of light except those around 500-570 nanometers, which is reflected instead. Now, when this reflected light enters our eyes, our brains percieve it as the color we call "green." I hope that clears things up for you.
</smarm>

Re:NEWS ALERT (Summary)

[digitalunity]

Hold still and this won't hurt a bit:

THE SKY IS NOT BLUE. Ok? The sky is composed of nitrogen and oxygen in large proportions. Both are transparent materials in gaseous form. They do, however, refract light like a prism. The fact that it appears blue is a matter of where on earth you are in relation to the sun. During a sunset, the sky is not blue and red, it is some shade in-between. As the light is refracted through the atmosphere, the color changes. If the sky were really blue, the moon and the stars at night would also look blue. Conversely, if the sky really were blue, the earth viewed from space would look like one solid blue ball.

If you look at a blue ball through the edge of a prism and it looks red, is the ball still blue? I think so.

Now, as to your general attitude: I'm really not important, and neither are you. I am however, not ignorant. I rarely open my mouth or hit the keys without really knowing what I'm talking about. I often attempt coy humor, which I'm obviously not very good at.

I would call you a pedant, if you were right. I would also welcome you to come back and talk with me after you pass a couple of High School science courses. This seems unlikely though because of your low user id. The only conclusion I can come up with: It is you who are ignorant.

water IS heavier than air

[mangu]

Clouds float because the water droplets in them are tiny, and have a large surface-to-volume ratio. If the force caused by the friction of rising air currents on the droplet's surface is larger than the weight of the droplet, the droplet rises with the air. When the droplets increase too much in size, it rains.

And what if the air in the cloud isn't rising? Then the water droplets fall, very slowly. If they are too small to cause rain, when they reach lower layers of the atmosphere they evaporate, because air lower down is, normally, warmer.

MASS != WEIGHT

[PSL]

Using the Largest Living Land Mammal to Calculate Cloud Mass... Ever wonder how much a cloud weighs?

MASS != WEIGHT

Bad Mathematician....no cookie

[Kris Warkentin]

a square meter is 100x100 square cm or 10000. So you have 500 * 10000 * 3 / 1000 = 15000kg

So a square km getting 3cm of rain would be 2000 times that (1000^2/500) which is 30 million kg.

not nearly enough elephants

[Yair]

Absolutely right. The article's estimate is way low.

In fact:

The 100,000 elephants is low even for today. And as recently as 1970 there were an estimated 1.5 million [toledozoo.org] wild elephants in Africa alone.

Fifty years isn't a bad guess for generations. this article [greennature.com] puts life-span at 60 years... but, ater factoring in early mortality, historical average life was probably much, much lower.

Continuing back-of-the-envelope calculations:

Let's say that an average historical elephant population was two million...

... and average life-span was twenty years...

... and assuming an historical period of, say, ten thousand years...

... suggests that two billion elephants ever lived.

Silly article.

Water (vapor) is lighter than air

[Sunlighter]

If you add up molecular weights and use the gas laws (PV=nRT), youll find that water vapor -- which is what clouds are made of, until they rain out -- is lighter than air.

The gas laws tell you basically that when P and T and R are constants, as they are in any small region of the atmosphere, the volume is proportional to the number of moles of gas that you have. I don't know how many cubic meters of gas make up a mole, up in the clouds, but I know it's a constant, and... a mole of N2 (nitrogen gas, which makes up 60% of the air) weighs 28 grams, and a mole of O2 (oxygen) weighs 32 grams, and a mole of CO2 (carbon dioxide) weighs 44 grams. But a mole of H20 weighs in at only 18 grams. So, water is lighter than air.

This is why barometric pressure decreases when clouds are overhead.