Talk:Cloud

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Peer review This article was externally reviewed on December 14, 2005 by Nature. It was found to have 5 errors.

I'm skeptical that Cumulonimbus with mammatus and pileus should be in the high altitude section rather than in section D. Can someone with greater authority in the area look this over? Dr. Z 19:03, 31 Mar 2004 (UTC)

can someone who knows about clouds add Coalescence, Ceilometer and Cloud base into this article so that Coalescence ceases from being an orphan? Kingturtle 23:09 May 13, 2003 (UTC)

(William M. Connolley 19:47, 2004 Mar 31 (UTC)) Done.


This from a duplicate page. some bits may need merging:

Contents

[edit] Cloud Types

Cumulus clouds are usually created through thermal convection or frontal lift.

See meteorology.

-- Tarquin

And which page is it from? I Wiki-searched and Googled without results. --Menchi 09:06 30 May 2003 (UTC)

[edit] Interesting topic that should be included.

I came across an interesting cloud question, and I think this arctile should cover this.

How much does a cloud weight?

here is one answer (detailed): http://www.weatherwise.org/qr/qry.cloudweight.html

[edit] More photographs available

I am an amateur photographer and have taken many cloud pictures. Anyone with an interest in adding more pictures to the right places may feel free to use my photographs. You can find them at my web site. I don't know what Wikipedia requires, but I will provide whatever is necessary to ensure release into the public domain.

--JeremyCole 09:01, Oct 30, 2004 (UTC)

[edit] Why do clouds stay aloft?

I came across a page that describes fully (and I believe correctly) why clouds stay aloft here: http://www.amasci.com/miscon/miscon4.html#cld

It appears that the Wikipedia and his reasoning are in conflict. In the Wiki article, you claim in the same paragraph that clouds wiegh several million tonnes and that updrafts keep all those tonnes of water up there. I don't know any updraft capable of holding that much water airborne. If there were such a thing, we should build a generator of one and build a city in the sky ;)

Joking aside, there is a very easy counter-example to site to disprove the 'small droplet' explanation. A cloud machine, like you see in the mall. Those small water dishes that generate 'clouds' The material doesn't rise and it certainly isn't slowed down by it's size (much).... it races to the floor!

The reason clouds remain aloft is that they are warmer inside than the surrounding air, so they float just like a hot air balloon! Simple.

Some of the dynamics sited in the article are certainly valid, such as the dynamic processes within a cloud. However they sidestep the reason millions of tonnes of water stay up there (and how.)

I have also noted the absence in many explanations of the source of cloud updrafts. Many people describe the strong updrafts within a thunderstorm and thier effects on a hapless pilots who may navigate them, but what it the source? It is a second proof of the temperature explanation of cloud bouyancy. Updrafts occur when the warmer air between water droplets is separated from the droplets and the warmer air shoots upward.

In other words, I can prove hot air is keeping the cloud up there. Because when it rains, hot air shoots skyward! It also shoots out of my mouth.

Mark DiNubila

  • Those "small droplets" produced by humidifiers and similar devices are huge relative to the droplets within clouds. If you doubt the power of air currents within clouds to maintain lift, go outside on the next foggy day and notice the effect of microturbulence on real droplets. Get a pair of binoculars and look at the edge of a cumulus cloud if you think rising air can't manage to keep droplets aloft. You may also check http://www.madsci.org/posts/archives/2005-06/1117621104.Es.r.html for an answer to the question in your title. Denni☯ 00:12, 2005 Jun 7 (UTC)
Please give evidence for your above assertion that "those 'small droplets' produced by humidifiers and similar devices are huge relative to the droplets within clouds." I suspect it's wrong. If typical cloud droplets fall at a few mm/second, then humidifier droplets must be far smaller, rather than larger: observe a bowl full of humidifer fog. The individual droplets fall much more slowly than a few mm/second. However, because sufficiently small droplets are essentially "stuck" in the surrounding air, a group of small neighboring droplets is able to drag the air between them downwards far faster than the droplets would fall individually. Droplet-filled air of sufficient density acts like a dense uniform gas, and will organize itself into a density current if given the opportunity to flow downwards. A similar effect is commonly seen in volcano plumes, where the rising cloud of hot gas and ash sometimes becomes more dense than surrounding air and therefore descends to form a ground-hugging pyroclastic surge. A flow of humidifier steam is analogous to a pyroclastic surge, where the individual particles may descend slowly, but the particle-laden air can flow downwards extremely rapidly. (This, though humidifier fog, like a pyroclastic surge, is considerably warmer than the surrounding air!) So, why does the droplet-laden air within clouds *NOT* form a descending plume? --Wjbeaty 02:52, 24 March 2006 (UTC)


  • What is the difference between fog and clouds? One thing... temperature differential!
  • What is the source of the 'updrafts' keeping clouds up there, at the edge of clouds? There is no external updraft! The forming of cloudstuff on the edge of clouds is the result of water vapor going from a gas to a liquid and heating the surrounding air, keeping it bouyant, even rising. There is no big fan on the edge of clouds blowing the material up holding it there.

MD

Its a combination of many different factors - hence the many different types of clouds. Some clouds stay aloft, some don't, and some are 80,000 metres above the ground (noctilucent clouds), some are 500. -- Natalinasmpf 23:54, 18 Jun 2005 (UTC)

Good point... my explanation on http://amasci.com/miscon/miscon4.html would apply to "typical clouds" and cannot be universal. For example, lenticular clouds and mountain wave clouds remain stationary in strong wind because they simultaneously condense at their leading edge and evaporate at their trailing edge. They are not physical objects at all, they are patterns, therefore the weight of the droplets is irrelevant. Another issue: the density of air is about 1.1KG/M^3, and if the added density contributed by the cloud droplets is insignificant compared to that of existing air, then no downward density current should arise, and the cloud should remain aloft simply because the individual droplets fall very slowly. (Similarly, if the temperature of a region of air is insignificantly lower than that of surrounding air, no downdraft should form.) What then is "insignificant?" If typical cloud-stuff increases the air's average density by about 1%, that's similar to making the air denser by cooling it by roughly 3 degC. Will a cloud-sized region of cold air form a downdraft if it's only 3 degC cooler than its surroundings? If so, then by analogy the increased density caused by cloud droplets must create a downdraft ...unless the condensation-warmed air in the cloud produces a compensating bouyant force. --Wjbeaty 03:01, 24 March 2006 (UTC)

[edit] Some Images

I uploaded these images, [1], [2] and [3], (image references obvious by their filename) - which are high altitude photos of clouds from Mount Kinabalu, and I was wondering if it would be appropriate to insert them in either the Mount Kinabalu Article or the Cloud article, because I know both of them are already image saturated. The thing is that I'm not too sure of all the cloud formation classifications (although it fascinates me) to insert them in specific pages either. -- Natalinasmpf 23:54, 18 Jun 2005 (UTC)

[edit] Cloud edges

The NY Times this morning (July 20) had a Q&A about why clouds have edges: "Q. Why do droplets of water form defined clouds rather than dispersing evenly into the atmosphere?" This is a common and interesting question, which sparks thought if it's the first time you've wondered about it. The response is provided by Geoff Cornish, a Penn State meteorologist: "... Clusters of millions of cloud droplets form in the updrafts. Over a larger area, Mr. Cornish continued, air cannot move upward without compensating subsiding air. This results in the clearly defined edges seen in cumulus clouds. The bottoms of clouds are where the parcel of air becomes saturated, and the top is where the upward impulse dies out, he said." A statement along these lines would fit in nicely here, especially if it could be expanded somewhat. -- Archie Paulson 16:07, 20 July 2005 (UTC)

[edit] High cloud heights

Both the Canadian MANOBS and [4] say that high clouds can form lower in polar regions. CambridgeBayWeather 09:15, 23 August 2005 (UTC)

[edit] Cloud article names

I suggest that the titles of cloud articles be changed to end with "cloud" so that they're consistent, with redirects from the previous names. -- Kjkolb 06:04, 19 October 2005 (UTC)

[edit] Cloud Identification

I'm really at a loss here. I have my Field Guide for North American Weather out, but I'm still not sure. What kind of cloud does this look like to you?

http://img128.imageshack.us/img128/7718/cirrostratusnebulosus7va.jpg

I was thinking Cirrostratus nebulosus, it certainly resembles the picture they have, but it also resembles several other pictures, especially the altostratus pictures. The description for cirrostratus says "Uniform, generally featureless, thin to thick, white or light gray ice-crystal clouds" and the description for altostratus says "Thin or thick, gray to pale blue, mainly water-droplet clouds at middle levels." The picture kind of fits both of those. The clouds seem somewhat whispy, so I'm leaning towards cirrus, but I'd rather have someone more knowledgeable say for sure.

PiccoloNamek 21:34, 26 November 2005 (UTC)

I just noticed your question. It's pretty hard to identify three dimensional clouds from a two dimensional picture. However, it looks as if there are at least two and maybe more cloud types in the picture. If you look at the cloud that is against the blue of the sky then I would say that it's Cirrus. The larger cloud mass above it (in the picture) may well be Cirrostratus but it woukld think that it's Altostratus. It appears to be lower in the sky than the centre Cirrus and looks a little too dark to be Cirrus. If you look at the bottom right just above the tree tops, there appears to be a third cloud. This could be a fractus of lower cloud or ACC forming. There's no way to judge the hight of it. CambridgeBayWeather (Talk) 17:48, 16 December 2005 (UTC)

[edit] Nature claims 5 errors

Nature disputes the accuracy of this article; see http://www.nature.com/news/2005/051212/multimedia/438900a_m1.html and Wikipedia:External_peer_review#Nature. We're hoping they will provide a list of the alleged errors soon. —Steven G. Johnson 01:53, 15 December 2005 (UTC)

So what!  :P - Hard Raspy Sci 04:19, 15 December 2005 (UTC)
Nature is a highly respected scientific publication that's what!--Deglr6328 22:22, 17 December 2005 (UTC)

[edit] Errors ID'd by Nature, to correct

The results of what exactly Nature suggested should be corrected is out... italicize each bullet point once you make the correction. -- user:zanimum

  • Under 'Cloud formation and properties', cloud formation happens when air is cooled below its saturation point, not to its saturation point.
  • Under 'Cloud formation and properties': 'The air stays the same temperature but absorbs more water vapour into it until it reaches saturation'. No. Droplet or ice particle formation requires supersaturation. Water vapour can only be added to bring the air to saturation.
  • Omission: Cloud can however be formed by the mixing of two subsaturated air masses. Examples of this are “breath” condensation on a cold day, arctic sea-smoke and aircraft contrail formation.
  • 'This method of raindrop production … typically produces smaller raindrops and drizzle'. Tradewind and tropical cumulus clouds are capable of producing drops of several millimetres in diameter.
  • Under 'clouds in family A': A contrail is a long thin cloud which develops as the result of the passage of a jet airplane at high altitudes. (any type of aircraft is capable of forming a contrail – not just jets. They result when mixing of the engine exhaust which contains unsaturated water vapour mixes with the unsaturated environmental air to produce a mixture which becomes temporarily saturated).

[edit] Why do cloud droplets not display rainbows?

When a cloud is composed of droplets, why don't they show as a rainbow when seen from the right direction? Are the droplets too small (compared to light wavelength)? I have a photo where a rainbow seems to be partly hidden behind clouds. (It was cold that day, almost freezing.) Abu ari 09:07, 21 March 2006 (UTC)

I would say because the water droplets are too densely packed. For an ideal rainbow to form, each light ray must be refracted by one, and only one, water drop. If a lot of the light makes it through without hitting a water drop, then you will get a pale rainbow. If each light ray is refracted by multiple drops of water, the colors will be randomly distributed all over the sky, with the net effect being white (or black if there are so many droplets that they actually absorb the light). Notice that you don't see rainbows in the midst of a serious rainstorm, either. StuRat 12:28, 21 March 2006 (UTC)
I see. Only a thin layer on the sunny side of the cloud is exposed to direct parallell rays from the sun. That layer does form a rainbow, but because the layer is thin, the intensity of the rainbow is too low to be seen. Abu ari 09:24, 22 March 2006 (UTC)
Wrong. It's because of diffraction, because the droplet size is too small. The best rainbows are caused by large raindrops, and as the raindrop size decreases, the colors blend together and numerous diffraction stripes appear within the curve of the rainbow. See cloudbow --Wjbeaty 03:26, 24 March 2006 (UTC)
Yes, without putting in numbers, it must be diffraction, due to the small size of the drops. The drops can't be too densely packed or the cloud would fall. A rainbow is a geometric optics effect involving reflection and refraction. Cloud particles are too small to be well described by geometric optics, as rain, and too large to be well described by Raleigh scattering, as air. (Since liquid cloud droplets are nearly spherical, they are well described by the Mie series). There are colored rings around the sun due to thin clouds. This may be a diffraction effect, more like Raleigh scattering. David R. Ingham 18:10, 1 May 2006 (UTC)

[edit] Colors of clouds

I am not convinced that the explanation of dark clouds is correct. At best it is incomplete. David R. Ingham 17:44, 1 May 2006 (UTC)

[edit] Some questions that the article could include

Here are some questions that I feel the article could answer a little more explicitly: - Why is there a layer of clear air between a cloud and the ground? - Why do water clouds have very sharply defined edges? - Why are the bottoms of cumuliform clouds pretty flat and uniform, when the tops are lumpy? - Why is there liquid water in clouds that reside in air up to 30 degrees below freezing? Some of the answers are hinted at, others aren't answered at all, but I think all are good questions, worthy of an answer in this article. Annihilatenow 11:09, 3 May 2006 (UTC)

[edit] Contrail dispute

I don't think that contrail should be listed along with the naturally occuring cloud formations in this article. It is a form of pollution, more akin to smog than to true clouds. — Morganfitzp 02:18, 13 September 2006 (UTC)

[edit] Banner clouds

I came to know of banner clouds from Talk:Matterhorn. There is also a link to a photo of a banner cloud in the discussion there. But I couldn't get any info on a banner cloud in this article or a mention of it in List of cloud types. Is there a technical name by which banner clouds are known ? Jay 08:19, 6 November 2006 (UTC)

[edit] Introduction

This is the first paragraph of the introduction as of 11/09/2006:

"A cloud is actually an assortment of dead jews this comes from WW2 times. Before this there were no clouds and afterwords clouds were there thanks to the burning dead jews.droplets jew tears or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body. The branch of meteorology in which clouds are studied is nephology."

I have no wiki experience, and I am not an expert nephologist by any means but this definition is ridiculous. If someone who has a greater scientific knowledge than myself has the time to offer a founded, definition for a cloud (or revert the vandalism) I think the article would be better for it. ngschmidt

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