Clouds can persist for hours - so why can't contrails do so too??

reply to post by Iwinder


Actually the regular air pollution from ground based sources, whether natural or anthropogenic, is in "regular" clouds. Think about the pictures of cities under a brown cloud of smog. Or the smoke from large fires. All are found in the atmosphere.
The only place exhaust fumes from a jet are any more toxic than your car are when they are on the ground, due to their concentration.

reply to post by Beartracker16

This exhaust is hot as it exits the jet engine and condenses as it strikes the cold atmospheric air forming the contrail, much as your breath on a cold day. This exhaust cools quickly to the ambient temperature and dissipates as the heat source ,jet engine, moves away.

Sort of. You left out the part about how the condensed water in a contrail freezes because of the extremely cold temperatures.
Those ice crystals may or may not evaporate immediately (sublimate) depending on how much water vapor is present in the air (humidity).

The same works with some clouds. For example a stratus deck is not formed by rising air from the surface but from a layer of saturated air.

Originally posted by Iwinder
reply to post by Aloysius the Gaul

 

And yes I know that "clouds" are "natural" and contrails are "artificial" - but nonetheless they are still both only water, so why do you insist they behave differently?

Perhaps because they are two different things composed of two different makeups?

Surely Jet exhaust contains things that natural clouds do not contain.

Yes jet exhaust does contain "other stuff" - CO2, CO, SOx, NOx, etc.

However the contrail that you see is just water.

and it is the same with clouds - there is more "stuff" in a cloud than just water - there is whatever pollutants might be in that particular pocket of air for example.

But the bit of the cloud you see if just water too.

reply to post by Iwinder

If you wish to clarify and say they are the "exact same" that would be a big help.

They aren't exactly the same. Early in the life of a contrail there are noticeable difference in things like the size and numbers of the ice crystals. The longer the contrail persists, the less pronounced these differences are.

And yes, there also are exhaust products in the contrail though they have nothing to do with the physical appearance or persistence of the contrail. And, over time, they dissipate, making the contrail less and less distinguishable from natural cirrus.

This is the best information I have yet found on this subject online at least. It is posted on the IPCC web site. The title and the link are here: Aviation and the Global Atmosphere.
I have not thought through the entire article as it is very long but it seems like changes over the years in fuel and fuel economy are the most relevant factors in this very recent man made phenomena. I hit on the same conclusions on this years ago before this paper was published and the CT crowd booed me off the stage more or less. I just gave up on this subject many many years ago but I post this here because it is the most definitive analysis I have been able to find on the subject.

reply to post by endats01

That is a good compendium of various research projects. I like this part:

Sky photographs taken from 1986 to 1996 over Salt Lake City, Utah, reveal a seasonal cycle in contrail frequency, with a maximum in fall and winter and a minimum in July (Sassen, 1997).

www.ipcc.ch...

It supports a "study" I did a while back. I found that "chemtrail" threads seem to follow a seasonal pattern.
www.abovetopsecret.com...

I find it funny that all of yall ignored my last comment.

reply to post by Infi8nity

I missed it. Bottom of the page. Sorry.

When you compare a small batch of ice to a larger batch of ice the smaller one will melt faster.

I'm not sure of your point but the ice crystals in a cirrus cloud (or contrail) don't melt, they sublimate.
They also aren't in a clump. Take hand full pieces of ice about the same size and spread them out. They'll all melt (or sublimate) at the same rate.

Originally posted by Infi8nity
Clouds are much more dense, they can wight tons.
greenearthfacts.com...

Assuming a blue whale is close to 160 (160,000 kg) tones in weight, a cumulus cloud weighs as much as 6,268.75 blue whales!

When you compare a small batch of ice to a larger batch of ice the smaller one will melt faster.

That's not really a good analogy though - while eth total mass might be in that order the clouds are made up of myraid small particles - they are not a single large particle themselves.

And they exist because of the atmospheric conditiosn that exist in that volume of the atmosphere - they can be affected as fast as conditions change throughout that volume.

So each miniscule droplet or ice crystal is being affected individually.

Originally posted by Phage
reply to post by Infi8nity

 

I missed it. Bottom of the page. Sorry.

When you compare a small batch of ice to a larger batch of ice the smaller one will melt faster.

I'm not sure of your point but the ice crystals in a cirrus cloud (or contrail) don't melt, they sublimate.
They also aren't in a clump. Take hand full pieces of ice about the same size and spread them out. They'll all melt (or sublimate) at the same rate.

edit on 3/6/2013 by Phage because: (no reason given)

Depends on how far they are apart. A cloud is dense, water is closer.
You cant really compare the 2, they are formed completely different.

I am positive that density effects the temperature of the of the whole. Sure they may sublimate but temperature is a factor.

reply to post by Infi8nity


Neither contrails nor cirrus clouds melt. I am unaware as to how ice will melt at minus 20 degrees and colder.

reply to post by Infi8nity

Depends on how far they are apart. A cloud is dense, water is closer.

Water is closer to what? The density of a cloud? I don't understand.

You cant really compare the 2, they are formed completely different.

The two what? I don't understand?

And again, I don't understand the point you are trying to make about melting ice.

I am positive that density effects the temperature of the of the whole. Sure they may sublimate but temperature is a factor.

Not so much. The main factor is the relative humidity with respect to ice.
Think about water. Does it evaporate faster on a day with low humidity or a day with high humidity?

Originally posted by Phage
reply to post by Infi8nity

 

Depends on how far they are apart. A cloud is dense, water is closer.

Water is closer to what? The density of a cloud? I don't understand.

You cant really compare the 2, they are formed completely different.

The two what? I don't understand?

And again, I don't understand the point you are trying to make about melting ice.

I am positive that density effects the temperature of the of the whole. Sure they may sublimate but temperature is a factor.

Not so much. The main factor is the relative humidity with respect to ice.
Think about water. Does it evaporate faster on a day with low humidity or a day with high humidity?

edit on 3/6/2013 by Phage because: (no reason given)

Water particles are closer to each other. The cloud is denser.
Come on we are disscussing 2 things clouds and contrails how could you not know what I was comparing. Your not going to tell me temperature has no effect on ice dissipating. I am sure some of it melts, some of it turns into gas.

reply to post by Infi8nity


How much effect do you think temperature can have if it never gets warmer than minus 20?

reply to post by Infi8nity

Come on we are disscussing 2 things clouds and contrails how could you not know what I was comparing.

Contrails are clouds. Clouds of ice crystals. Cirrus clouds are clouds of ice crystals.
Lower level clouds are composed of water droplets instead of ice crystals but the same principle applies. A deck of stratus clouds is a deck of water droplets. Water droplets which will not evaporate because the relative humidity (with respect to water) is 100%.

Your not going to tell me temperature has no effect on ice dissipating. I am sure some of it melts, some of it turns into gas.

At the altitudes at which clouds form the temperature never gets above freezing. Ice cannot melt at that altitude, it can only sublimate and it does that because of the low atmospheric pressure.

Originally posted by Phage
reply to post by Infi8nity

 

Water particles are closer to each other. The cloud is denser.

The cloud is denser than what?

Your not going to tell me temperature has no effect on ice dissipating. I am sure some of it melts, some of it turns into gas.

At the altitudes at which clouds form the temperature never gets above freezing. Ice cannot melt at that altitude, it can only sublimate and it does that because of the low atmospheric pressure.

edit on 3/6/2013 by Phage because: (no reason given)

Seriously come on man. Clouds are denser then contrails......

en.wikipedia.org...

Sublimation is an endothermic phase transition that occurs at temperatures and pressures.

reply to post by Infi8nity

I edited my post before I saw yours.

Clouds are denser then contrails

Contrails are clouds.

Sublimation is an endothermic phase transition that occurs at temperatures and pressures

You forgot this part of the statement and added a period that didn't belong there.

below a substance's triple point in its phase diagram.

en.wikipedia.org...
The triple point is freezing point for most purposes. The ice in contrails doesn't melt. It sublimates.

Originally posted by Infi8nity
When you compare a small batch of ice to a larger batch of ice the smaller one will melt faster.

edit on 6-3-2013 by Infi8nity because: (no reason given)

That's a bad analogy. here's a better one:

On a sunny warm day, a football field covered with a layer of snow will melt at the same rate as my front yard covered with a layer of snow.

Originally posted by Infi8nity

Seriously come on man. Clouds are denser then contrails......

Cirrus clouds can be quite thin, and not very "tall" (that's why you can often see through a cirrus cloud). Cirrus clouds can last for hours. Cumulus clouds are a lot denser and taller, but nobody is comparing a contrail to a cumulus cloud.

Originally posted by Phage
reply to post by Infi8nity

 

I edited my post before I saw yours.

Clouds are denser then contrails

Contrails are clouds.

Sublimation is an endothermic phase transition that occurs at temperatures and pressures

You forgot this part of the statement and added a period that didn't belong there.

below a substance's triple point in its phase diagram.

en.wikipedia.org...
The triple point is freezing point for most purposes. The ice in contrails doesn't melt. It sublimates.

edit on 3/6/2013 by Phage because: (no reason given)

Your trying to annoy me right? Its not working bud
You know exactly what I mean I do not have to be detailed for you to understand. Yes contrails are clouds but clouds are not contrails.

Explain to me how a contrail expands into a massive line witch reflects sun light. The sun directly pounding on it, you can see a orange glow from it. Their is no way it would remain frozen.

I dont even know why im arguing with you guys.
Its to obvious, any one thats be on this forum a while knows what happens in this section.
I want to leave this site but on the other hand, I can bring allot to the table.

reply to post by Infi8nity

Your trying to annoy me right?

No. I'm trying to answer your questions.

Explain to me how a contrail expands into a massive line witch reflects sun light. The sun directly pounding on it, you can see a orange glow from it. Their is no way it would remain frozen.

Ok. Contrails are white, they reflect sunlight. Because they reflect sunlight, they don't absorb a lot of heat. That's part of the answer. The rest of it is, it's very very cold up there.

Now, explain why cirrus clouds cover many hundred square miles of sky with the sun shining on them the whole time?
(hint: see above)