FREE TAPATALK APP

Brown · 3rd September 2003, 06:01 PM

Articles like this one from ABC News illustrate that real science is much more interesting than pseudoscience:

Quote:

Let's start with a very simple white puffy cloud — a cumulus cloud. How much does the water in a cumulus cloud weigh? Peggy LeMone, senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, did the numbers.

"The water in the little cloud weighs about 550 tons," she calculates.

The article provides a hint as to how a multi-ton mass can remain suspended in mid-air... but I understand that a full explanation as to why clouds float is a bit more complicated, and the article does not go into detail on this point.

The author describes weight of the cloud in "units" of elephants. But of course, one could also describe the weight as a number of average-sized people--about 7000 of them--or Ten Commandments monuments--over 220 of them.

UnrepentantSinner · 3rd September 2003, 06:11 PM

Robert Crulwitch is great. It's thanks to him that I know what the song Frere Jacques is all about. And I saw the cloud installment when it aired, it was very well done.

Cinorjer · 4th September 2003, 04:26 AM

On a related note, I've read about what clouds are made of (water vapor and dust), but no one has ever explained to my satisfaction what causes a fluffy cloud to "clump". After all, water vapor and dust make up the average fog. It seems logical that the clouds would just sort of spread out in the atmosphere. Can anyone enlighten me? I have a 3 year old Grandson who will probably ask me one day, and I'd like to be ready.

whitefork · 4th September 2003, 05:32 AM

Now for a little walk down memory lane:

http://www.h2net.net/p/nslade/cloud.html

arcticpenguin · 4th September 2003, 06:52 AM

I've looked at clouds from both sides now,
from up and down,
and still somehow...

wollery · 4th September 2003, 07:15 AM

Quote:

Originally posted by Cinorjer
On a related note, I've read about what clouds are made of (water vapor and dust), but no one has ever explained to my satisfaction what causes a fluffy cloud to "clump". After all, water vapor and dust make up the average fog. It seems logical that the clouds would just sort of spread out in the atmosphere. Can anyone enlighten me? I have a 3 year old Grandson who will probably ask me one day, and I'd like to be ready.

Actually they don't. If you watch time lapse photography of clouds they grow/shrink coalesce/disperse constantly. It just happens on time scales that are a fair bit longer than most people will ever watch them on.

Brown · 4th September 2003, 07:24 AM

Quote:

Originally posted by Cinorjer
On a related note, I've read about what clouds are made of (water vapor and dust), but no one has ever explained to my satisfaction what causes a fluffy cloud to "clump".

This is a really good question, and I regret that I do not have an answer. A few years ago, I read a fascinating article about clouds in a well-known science magazine (possibly Scientific American), that explained why clouds float, why clouds "clump," why clouds appear and disappear, etc. Unfortunately, I haven't been able to track down that article yet.

A lot of contributors to this forum are really good at identifying web sites that provide reliable answers to questions like these. Maybe they can help...?

MRC_Hans · 4th September 2003, 07:29 AM

[RANT=LONG]
First on cloud-busting: Nice trick! You could impress your friends with this. Note the selection of clouds: On a calm day, a small cloud with fluffy edges surrounded by bigger clouds. That is the precise description of a cloud in the process of dissolving. Within 8-10 minutes (or less), such a cloud will almost always dissolve, whether you concentrate on it or not.

On the weight of clouds: Atmospheric air weights about 1.3kg/cubic meter at sea level. Of course, most clouds are rather big, so they contain a lot of air (and a comparatively low amount of water droplets and dust), so figuring out its weight will yield a surprisingly large figure, but as long as its density is the same as the surrounding air, it will stay there. The small extra weignt from water and dust is compensated by the fact that the air inside the cloud is slightly warmer than the surrounding air.

How clouds form: Clouds form basically when air is cooled. The amount of water vapour that air can hold depends very much on temperature; the warmer the air, the more it can hold. Note that Water vapour is invisible; the visible part of clouds consists of microscopic water droplets.

Air gets cooled when it rises. This is a little contra-intuitive, since everybody knows that warm air rises, and most people know that the air under the ceiling of a room is generally warmet than at the floor. However, on a climatic scale, when air riese, the pressure drops, and therefore the rising air expands. Expanding air gets cooler (you might say that the warmth is also thinned).

Air can rise for several reasons. On a summer's day, the ground is heated by the sun, some parts get heated more than others. Over a hot (and large) surface the air gets warmed more than the surrounding air, and now boing lighter, it will start to rise. As it rises, it expands and cools (but it is still warmer than the surrounding air). If it does not rise much, the cooling will stabilize the situation, and nothing happens, but if it rises above a certain altitude (which depends on a number of factors), it will get so cool that it can no longer hold all the water vapour in it. The water vapour will start to condense into water droplets: A cloud is born!

When water condenses, it releases the heat originally used to turn it into vapour. This is quite a lot of heat, it represents the same amount of energy that would be needed to raise the temperature about 480 degrees celcius. Because this energy is released while the air is rising, the temperature of the rising air is kept nearly constant as it rises further, and as the surrounding air keeps getting colder with altitude, the air shoots up turbulently, forming the cauliflower-shape we know as a cumulus cloud.

So while such clouds look like big things floating along, they are really in constant internal motion and they are only the visible part of a wind-system that extends both above and below the cloud.

Other things that can make air rise and form clouds include meteorological fronts and mountains.[/rant]

Hans

Crossbow · 4th September 2003, 08:37 AM

A couple of months ago I taught a class in how hot air balloons and helium balloons work and I had a pretty good handle on the general idea but I did not know all of the details. So prior to the class I looked up some data such as the density of the air (at various temperatures), and the density of hydrogen, and helium.

Anyway, using the air density data, and reducing it by 5% to account for the water vapor, I did some rough calculations based on a cloud 100 yards in diameter and 50 feet thick, and sure enough, the weight was about 500 tons.

Cool!

Even though I have worked in meteorology and airplanes for many years I have never really thought about 'weighing a cloud' until this thread.

Thanks man! That is a good way to think of it and I will try to work it in if I ever teach a similar class again.

3rd September 2003, 06:01 PM	#1
Brown Penultimate Amazing Join Date: Aug 2001 Location: Twin Cities, Canada Posts: 12,293	How Much Does A Cloud Weigh? Articles like this one from ABC News illustrate that real science is much more interesting than pseudoscience: Quote: Let's start with a very simple white puffy cloud — a cumulus cloud. How much does the water in a cumulus cloud weigh? Peggy LeMone, senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, did the numbers. "The water in the little cloud weighs about 550 tons," she calculates. The article provides a hint as to how a multi-ton mass can remain suspended in mid-air... but I understand that a full explanation as to why clouds float is a bit more complicated, and the article does not go into detail on this point. The author describes weight of the cloud in "units" of elephants. But of course, one could also describe the weight as a number of average-sized people--about 7000 of them--or Ten Commandments monuments--over 220 of them.
	__________________ Klaatu: I'm impatient with stupidity. My people have learned to live without it. Mr. Harley: I'm afraid my people haven't. I am very sorry. I wish it were otherwise. -- The Day The Earth Stood Still, screenplay by Edmund H. North "Don't you get me wrong. I only want to know." -- Judas in Jesus Christ Superstar, lyrics by Tim Rice

3rd September 2003, 06:11 PM	#2
UnrepentantSinner A post by Alan Smithee Join Date: Aug 2001 Location: USAian is not a word Posts: 26,438	Robert Crulwitch is great. It's thanks to him that I know what the song Frere Jacques is all about. And I saw the cloud installment when it aired, it was very well done.
	__________________ I am an American citizen who is part of American society and briefly served in the American armed forces. I use American dollars and pay taxes that support the American government. And yes, despite the editorial decison to change American politics to the nonsensical "USA politics" subforum, I follow and comment on American politics.

4th September 2003, 04:26 AM	#3
Cinorjer Thinker Join Date: May 2003 Posts: 242	On a related note, I've read about what clouds are made of (water vapor and dust), but no one has ever explained to my satisfaction what causes a fluffy cloud to "clump". After all, water vapor and dust make up the average fog. It seems logical that the clouds would just sort of spread out in the atmosphere. Can anyone enlighten me? I have a 3 year old Grandson who will probably ask me one day, and I'd like to be ready.
Cinorjer Thinker Join Date: May 2003 Posts: 242	__________________ Exos Integro, Sugiliato Curatio, y Feminae Amo Cicatrix (Gladiator's Creed)

4th September 2003, 05:32 AM	#4
whitefork None of the above Join Date: Aug 2001 Location: aka kullervo Posts: 2,339	Now for a little walk down memory lane: http://www.h2net.net/p/nslade/cloud.html
	__________________ Convictions are more dangerous enemies of truth than lies - Nietzsche

4th September 2003, 06:52 AM	#5
arcticpenguin woo ban clan Join Date: Sep 2002 Posts: 5,717	I've looked at clouds from both sides now, from up and down, and still somehow...
	__________________ The power of accurate observation is frequently called cynicism by those who don't have it. - George Bernard Shaw

4th September 2003, 07:15 AM	#6
wollery Protected by Samurai Hedgehogs! Join Date: Feb 2003 Location: Land of Eternal Hope Posts: 10,332	Quote: Originally posted by Cinorjer On a related note, I've read about what clouds are made of (water vapor and dust), but no one has ever explained to my satisfaction what causes a fluffy cloud to "clump". After all, water vapor and dust make up the average fog. It seems logical that the clouds would just sort of spread out in the atmosphere. Can anyone enlighten me? I have a 3 year old Grandson who will probably ask me one day, and I'd like to be ready. Actually they don't. If you watch time lapse photography of clouds they grow/shrink coalesce/disperse constantly. It just happens on time scales that are a fair bit longer than most people will ever watch them on.
	__________________ "You're a sick SOB. You know that, Wollery?" - Roadtoad "Just think how stupid the average person is, and then realize that half of them are even stupider!" --George Carlin

4th September 2003, 07:24 AM	#7
Brown Penultimate Amazing Join Date: Aug 2001 Location: Twin Cities, Canada Posts: 12,293	Quote: Originally posted by Cinorjer On a related note, I've read about what clouds are made of (water vapor and dust), but no one has ever explained to my satisfaction what causes a fluffy cloud to "clump". This is a really good question, and I regret that I do not have an answer. A few years ago, I read a fascinating article about clouds in a well-known science magazine (possibly Scientific American), that explained why clouds float, why clouds "clump," why clouds appear and disappear, etc. Unfortunately, I haven't been able to track down that article yet. A lot of contributors to this forum are really good at identifying web sites that provide reliable answers to questions like these. Maybe they can help...?
	__________________ Klaatu: I'm impatient with stupidity. My people have learned to live without it. Mr. Harley: I'm afraid my people haven't. I am very sorry. I wish it were otherwise. -- The Day The Earth Stood Still, screenplay by Edmund H. North "Don't you get me wrong. I only want to know." -- Judas in Jesus Christ Superstar, lyrics by Tim Rice

4th September 2003, 07:29 AM	#8
MRC_Hans Penultimate Amazing Join Date: Aug 2002 Location: Whithin earshot of the North Sea Posts: 16,604	[RANT=LONG] First on cloud-busting: Nice trick! You could impress your friends with this. Note the selection of clouds: On a calm day, a small cloud with fluffy edges surrounded by bigger clouds. That is the precise description of a cloud in the process of dissolving. Within 8-10 minutes (or less), such a cloud will almost always dissolve, whether you concentrate on it or not. On the weight of clouds: Atmospheric air weights about 1.3kg/cubic meter at sea level. Of course, most clouds are rather big, so they contain a lot of air (and a comparatively low amount of water droplets and dust), so figuring out its weight will yield a surprisingly large figure, but as long as its density is the same as the surrounding air, it will stay there. The small extra weignt from water and dust is compensated by the fact that the air inside the cloud is slightly warmer than the surrounding air. How clouds form: Clouds form basically when air is cooled. The amount of water vapour that air can hold depends very much on temperature; the warmer the air, the more it can hold. Note that Water vapour is invisible; the visible part of clouds consists of microscopic water droplets. Air gets cooled when it rises. This is a little contra-intuitive, since everybody knows that warm air rises, and most people know that the air under the ceiling of a room is generally warmet than at the floor. However, on a climatic scale, when air riese, the pressure drops, and therefore the rising air expands. Expanding air gets cooler (you might say that the warmth is also thinned). Air can rise for several reasons. On a summer's day, the ground is heated by the sun, some parts get heated more than others. Over a hot (and large) surface the air gets warmed more than the surrounding air, and now boing lighter, it will start to rise. As it rises, it expands and cools (but it is still warmer than the surrounding air). If it does not rise much, the cooling will stabilize the situation, and nothing happens, but if it rises above a certain altitude (which depends on a number of factors), it will get so cool that it can no longer hold all the water vapour in it. The water vapour will start to condense into water droplets: A cloud is born! When water condenses, it releases the heat originally used to turn it into vapour. This is quite a lot of heat, it represents the same amount of energy that would be needed to raise the temperature about 480 degrees celcius. Because this energy is released while the air is rising, the temperature of the rising air is kept nearly constant as it rises further, and as the surrounding air keeps getting colder with altitude, the air shoots up turbulently, forming the cauliflower-shape we know as a cumulus cloud. So while such clouds look like big things floating along, they are really in constant internal motion and they are only the visible part of a wind-system that extends both above and below the cloud. Other things that can make air rise and form clouds include meteorological fronts and mountains.[/rant] Hans
	__________________ Don't. Just don't.

4th September 2003, 08:37 AM	#9
Crossbow Seeking Honesty and Sanity Join Date: Oct 2001 Posts: 6,349	A couple of months ago I taught a class in how hot air balloons and helium balloons work and I had a pretty good handle on the general idea but I did not know all of the details. So prior to the class I looked up some data such as the density of the air (at various temperatures), and the density of hydrogen, and helium. Anyway, using the air density data, and reducing it by 5% to account for the water vapor, I did some rough calculations based on a cloud 100 yards in diameter and 50 feet thick, and sure enough, the weight was about 500 tons. Cool! Even though I have worked in meteorology and airplanes for many years I have never really thought about 'weighing a cloud' until this thread. Thanks man! That is a good way to think of it and I will try to work it in if I ever teach a similar class again.
	__________________ A man's best friend is his dogma.