Clouds

[StringJunky]

What are the contributing factors that keep atmospheric clouds in a compact state as opposed to diffusing out uniformly which is what I expect gases to do normally?

 

This is a question prompted by my nephew that I couldn't adequately explain. I said they were a bit like steam but he said: "Why doesn't it spread out and disappear then?!"

 

If you can put your responses appropriate to a bright six year old I'll let him read them....his name's William.

 

Thanks.

Edited June 8, 2010 by StringJunky

[swansont]

They do, to some extent. Have you ever watched a time-lapse of clouds?

 

http://blogs.scienceforums.net/swansont/archives/5312

[iNow]

If I were to guess, I would suggest it has to do with the hydrogen bonds from all of the water. Basically, they are held together by basic chemical forces, and only when those forces are stretched or overcome by wind or something will they dissipate. That's just a guess, though.

[swansont]

Clouds are made up of small droplets, not vapor (i.e. not gaseous H2O). I suspect that once you start to condense the water (on some nucleation particle, like a speck of dust or dirt) it will tend to grow to a certain size until it hits steady-state, whether liquid or frozen. So the question becomes why these droplets conglomerate.

[D H]

The question "why do clouds exist?" is intimately tied with the question "why do we have weather?". We have weather because

• The Earth's equatorial regions receive a lot more solar energy than do the poles. That means the equatorial regions are hotter than the poles, and that in turn means that the atmosphere is going to move around to transfer energy from the equatorial regions to the poles.
  
• The Earth's surface is about 71% water, 29% land. Air over the oceans will naturally be fairly humid. When that humid air blows over land all kinds of havoc will break loose.
  
• Humid air is less dense than is dry air at the same temperature and pressure. When humid air confronts dry air that humid air will rise.
  
• The packet of rising humid air will expand (atmospheric pressure decreases with increasing altitude) and cool off (conservation of energy) as it rises.
  
• While the absolute humidity of the packet of rising humid air won't change, the relative humidity will. The temperature of the rising packet of humid air will eventually fall below the dew point.
  
• A cloud forms when the packet of rising humid air reaches that critical altitude.
  
• Warm air is less dense than is cool air at the same pressure. Combine warm moist air with cool dry air and things can become quite violent. Now the clouds are fueled by humidity and temperature differences.

 

These phenomena can happen very fast. Diffusion is a comparatively slow process.

[StringJunky]

Between you I think you've explained and demonstrated what I need to know to explain to him. My own guess was a combination of a fairly weak molecular attraction, atmospheric pressure surrounding the cloud and viewing them from a long distance which gives the impression of stability when in fact, close up, they are quite turbulent and not so static looking. That video does show that they dissipate eventually like gases aided by the wind...it just needed speeding up.

 

Cheers

[michel123456]

The question "why do clouds exist?" is intimately tied with the question "why do we have weather?". We have weather because

• The Earth's equatorial regions receive a lot more solar energy than do the poles. That means the equatorial regions are hotter than the poles, and that in turn means that the atmosphere is going to move around to transfer energy from the equatorial regions to the poles.
  
• The Earth's surface is about 71% water, 29% land. Air over the oceans will naturally be fairly humid. When that humid air blows over land all kinds of havoc will break loose.
  
• Humid air is less dense than is dry air at the same temperature and pressure. When humid air confronts dry air that humid air will rise.
  
• The packet of rising humid air will expand (atmospheric pressure decreases with increasing altitude) and cool off (conservation of energy) as it rises.
  
• While the absolute humidity of the packet of rising humid air won't change, the relative humidity will. The temperature of the rising packet of humid air will eventually fall below the dew point.
  
• A cloud forms when the packet of rising humid air reaches that critical altitude.
  
• Warm air is less dense than is cool air at the same pressure. Combine warm moist air with cool dry air and things can become quite violent. Now the clouds are fueled by humidity and temperature differences.

 

These phenomena can happen very fast. Diffusion is a comparatively slow process.

 

A question about that triggers me:

How come that the climate is so chaotic and has not stabilized in fluent currents, like trade winds? The earth is 4 billions years of age, it should have been enough time. Or is there something that continously destabilize the system and makes it chaotic?

[StringJunky]

Clouds are made up of small droplets, not vapor (i.e. not gaseous H2O). I suspect that once you start to condense the water (on some nucleation particle, like a speck of dust or dirt) it will tend to grow to a certain size until it hits steady-state, whether liquid or frozen. So the question becomes why these droplets conglomerate.

 

If I remember correctly from a James Lovelock's book "The Revenge of Gaia" the main nucleation material is dimethyl sulphide produced by oceanic algae. Would there be net charges in these droplets that cause them to conglomerate at some point?

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A question about that triggers me:

How come that the climate is so chaotic and has not stabilized in fluent currents, like trade winds? The earth is 4 billions years of age, it should have been enough time. Or is there something that continously destabilize the system and makes it chaotic?

 

There are random natural events like volcanic activity spewing out millions of tons of light blocking (cooling) and nucleating particles (rain forming) which would help to maintain a constant state of disequilibrium in weather patterns.

 

As I mentioned earlier algae-produced dimethyl sulphide which, I think if Lovelock is correct, is a precursor to the formation of rain clouds would also be dynamic in the amount that is produced according to the algae population which are dependent on the abundance of nutrients, which in turn is dependent on the ocean temperature....if it's too warm the nutrients stay locked at the bottom of the ocean (Can't remember the mechanism).

 

The population of all Earth life itself is dynamic and the byproducts they produce combined would effect long term climate patterns as well I would think.

Edited June 8, 2010 by StringJunky

[D H]

How come that the climate is so chaotic?

Whether climate is chaotic is an open issue. Whether weather is chaotic is not an open issue. All it takes is the flap of a butterfly's wing in Brazil to eventually to set off a tornado in Texas. Turbulence is an integral part of weather. This alone makes weather inherently chaotic. Weather is predictable for a week or so at most.

[StringJunky]

Whether climate is chaotic is an open issue. Whether weather is chaotic is not an open issue. All it takes is the flap of a butterfly's wing in Brazil to eventually to set off a tornado in Texas. Turbulence is an integral part of weather. This alone makes weather inherently chaotic. Weather is predictable for a week or so at most.

 

I never realised 'til now you mention it there's a difference between Climate and Weather:

 

What Climate Means

 

In short, climate is the description of the long-term pattern of weather in a particular area.

 

Some scientists define climate as the average weather for a particular region and time period, usually taken over 30-years. It's really an average pattern of weather for a particular region.

 

When scientists talk about climate, they're looking at averages of precipitation, temperature, humidity, sunshine, wind velocity, phenomena such as fog, frost, and hail storms, and other measures of the weather that occur over a long period in a particular place.

 

For example, after looking at rain gauge data, lake and reservoir levels, and satellite data, scientists can tell if during a summer, an area was drier than average. If it continues to be drier than normal over the course of many summers, than it would likely indicate a change in the climate.

 

http://www.nasa.gov/mission_pages/noaa-n/climate/climate_weather.html

 

Based on the 30 year 'sets' of observations that make up a region's climate it would take a good lifetime or two to see if substantial climate change had really occurred wouldn't it and that any given set is not just a 'blip' in the long term trend?

[michel123456]

Whether climate is chaotic is an open issue. Whether weather is chaotic is not an open issue. All it takes is the flap of a butterfly's wing in Brazil to eventually to set off a tornado in Texas. Turbulence is an integral part of weather. This alone makes weather inherently chaotic. Weather is predictable for a week or so at most.

 

I don't think turbulence is an integral part of weather, meaning, if I understand your point, that turbulence is inherent. Turbulences are caused by outside parameters, like Life (as mentioned by StringJ), that's the butterfly, and volcanoes (cf StringJ) which are phenomenas caused by other turbulences inside Earth's shell.

I was thinking that if you take a chaotic model representing weather and let it evolve freely without any disturbance (no life & no volcanoes), only with the parameters of rotation (coriolis force), other astral movements & relief, I guess the model should become regular i.e. not chaotic any more.

[cypress]

What are the contributing factors that keep atmospheric clouds in a compact state as opposed to diffusing out uniformly which is what I expect gases to do normally?

 

As another poster indicated, the cloud has water in vapor and liquid/solid form. The water and ice diffuses slowly compared to vapor.

 

As an experiment consider the time it takes for a pan of water to evaporate verses a recirculating fountain or spray of water to get an idea of what is going on.

[pioneer]

The hydrogen bonding of water plays a major role in the formation of clouds. One will not see clouds of nitrogen or oxygen gas within the atmosphere, even though these gases dominate the atmosphere and experience all the same solar, wind and temperature conditions. They don't make much use of H-bonding unless initiated by the water.

 

Although hydrogen bonding may seem trivial, to give one a feel for the amount of energy;

 

The formation reaction for liquid water is described by the following equation:

H2 (g) + ½O2 (g) → H2O(l) + 285.8 kJ

 

The amount of energy released during this reaction, 285.8 kJ, is referred to as the standard heat of formation.

 

Hydrogen bond dissociation energy in water is about 23 kJ/mol.

 

Imagine if up to 8% of the water in the atmosphere was replaced by H2 and O2 gas being burnt. That is the theoretical potential energy associated with the H-bonds, as we go from humidity all the way to liquid water. Clouds act as a step down toward lower energy. If we step down quickly, such as in thunder clouds the energy is released much quicker. This extra energy is like a wild card which can make some weather events hard to predict, unless one does an energy balance.

[JohnB]

Based on the 30 year 'sets' of observations that make up a region's climate it would take a good lifetime or two to see if substantial climate change had really occurred wouldn't it and that any given set is not just a 'blip' in the long term trend?

 

Which is why the paleoclimate record is so important. Using good direct measurements we can only go back to 1880 or so, the paleo record allows us to compare with longer timelines.

 

BTW. One of the best descriptions of the difference between climate and weather that I've seen is;

 

"Climate is what you can on average expect, weather is what you get."

[D H]

The hydrogen bonding of water plays a major role in the formation of clouds.

No. That water can exist in all three states in Earth's atmosphere plays a major role in the formation of clouds in the Earth's atmosphere. You wouldn't expect to see water clouds on Venus (no water) or on Pluto (too cold). Clouds on Venus are composed of carbon dioxide and sulfuric acid; clouds on Pluto are composed of nitrogen and carbon monoxide.

 

One will not see clouds of nitrogen or oxygen gas within the atmosphere, even though these gases dominate the atmosphere and experience all the same solar, wind and temperature conditions.

The critical temperatures of N₂ and O₂ are 126K and 155K, respectively. One will not see clouds of nitrogen or oxygen gas because nitrogen and oxygen remain gases throughout Earth's atmosphere. It has nothing to do with hydrogen bonds. One might well expect to see clouds of nitrogen on a very cold planet such as Pluto, and that is precisely what is seen there. For example, see http://www.sciencenews.org/view/generic/id/50424/title/Plutos_cloud_components_verified_.

[pioneer]

Other planets, with atmospheres do form clouds, using other chemicals, but I assumed the discussion was talking about the earth.

 

Other planets, like Venus have much higher pressures in their atmosphere. Water doesn't need the same pressures to form clouds. Ironically, rain clouds are usually associated with low pressure system and not high pressure systems.

 

Forming clouds can pull a vacuum; create low pressure. This is due to the strength of the H-bonding. As the vapor water condenses from gas to liquid/solid the volume occupied the water drops by a factor of 700. This removes the partial pressure contribution of the gaseous water.

 

If you ever did canning, one heats the open jar. Then we put on the lid. As the jar cools and the water condenses, it will pull a vacuum.

 

If we look at the BP of water as a function of pressure, one will notice water should condense quicker at high pressure, yet rain and most clouds on earth are more common in low pressure systems.

 

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An interest cloud that makes use of the condensation vacuum is a thunder cloud. The ground for many square miles might have similar high humidity, for example, over the western plains of the USA. The extra water in the warm humid air makes the air lighter, causing it to rise.

 

But the warm air does not always rise uniformly, to form a uniform bank of clouds. Sometimes extra warm air will funnel into a tall thunder cloud. The rising air condenses and solidifies, fastest in the thunder cloud, pulling the main vacuum. A tornado is a good way to connect the potential between the vacuum and the ground; faster than just a simple flow.

 

With a thunder cloud, we are also dealing with the energy released due to hydrogen bonding potential lowering. This energy calculates to having 8% of the water vapor flowing into the cloud, a O2/H2 burn, but using a cool phase change burn. This drives the condensation vacuum engine with the waste energy going into entropy. The clouds begin to act funny. The result is our thunder system can get somewhat unpredictable due to the entropy potential. But it can't become more unpredictable than the value of its energy source, since entropy needs energy and can't exceed its supply.

[Ophiolite]

BTW. One of the best descriptions of the difference between climate and weather that I've seen is;

 

"Climate is what you can on average expect, weather is what you get."

I prefer the same distinction carried with a frisson of wit in this observation:

 

"The climate in Scotland is excellent. It's the weather that is bloody awful!"

[swansont]

Forming clouds can pull a vacuum; create low pressure. This is due to the strength of the H-bonding. As the vapor water condenses from gas to liquid/solid the volume occupied the water drops by a factor of 700. This removes the partial pressure contribution of the gaseous water.

 

If you ever did canning, one heats the open jar. Then we put on the lid. As the jar cools and the water condenses, it will pull a vacuum.

 

A cloud has no lid, though. Pressure will equalize.

 

If we look at the BP of water as a function of pressure, one will notice water should condense quicker at high pressure, yet rain and most clouds on earth are more common in low pressure systems.

 

The vapor pressure of water is significantly lower than that of Nitrogen or Oxygen, the most likely molecules the water would replace

 

http://en.wikipedia.org/wiki/Vapor_pressure#Examples

 

So when you replace an amount of gas with a vapor pressure of ~50 MPa with one that's at 2.3 kPa, the overall pressure goes down. More water vapor results in a lower pressure of the system.

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Just ran across this

 

http://news.nationalgeographic.com/news/2010/06/100616-planes-change-weather-hole-punch-clouds-science/