Chemtrails on vacations?

reply to post by geobro


Contrails are cirrus clouds. That logic would mean that cirrus clouds can't last either.

There weren't as many persistent contrails before because they didn't have the high bypass turbofans they do today. The more efficient they are the more contrails they leave, and the more of then linger.

Originally posted by geobro
reply to post by stars15k

 

i did not say the pilot believed in chemtrails just that contrails were vapour and should only last a certain amount of time .

i do not ever remember seeing the effects i see now when i was younger even in the same weather conditions

You say "even in the same weather conditions". Mind giving us some insight as to how you can, at ANY time, see what the weather conditions are at 30k feet by just looking up? Please do keep in mind that the weather conditions on the ground have absolutely nothing to do with the conditions up there.

reply to post by Zaphod58

A clarification/correction.

The persistence of contrails is determined by primarily one factor, the ambient humidity with respect to ice. If the air is saturated (at a minimum) contrails will persist. If it is not they will not. It doesn't matter what sort of engine produces the contrail.

If the air is saturated (or supersaturated) the ice crystals will not sublimate so the contrail persists.

If the ambient vapor pressure is greater than or equal to the saturation vapor pressure with respect to ice, a persistent contrail will form for temperatures less than or equal to the points along the appropriate mixing line.

www-pm.larc.nasa.gov...

reply to post by Phage


Yes, but we're seeing more persistence with the newer engines than we did with the older engines. The only thing changing are the engine bypass ratios.

reply to post by Zaphod58

Yes, but we're seeing more persistence with the newer engines than we did with the older engines.

No.
We are seeing more contrails because there are more flights. The determining factor in persistence is RHI.

I haven't seen ANY planes fly by, in about a month. I wonder if they've changed route? Not even a "contrail" in the sky. Weird.

reply to post by WonderBoi

You don't usually notice planes 7 miles overhead unless they are producing a contrail.

But generally speaking contrails of any sort are less likely to form in the summer. Not surprisingly, we hear less about them on ATS at this time of year.
www.abovetopsecret.com...

Originally posted by flyswatter

Originally posted by geobro
reply to post by stars15k

 

i did not say the pilot believed in chemtrails just that contrails were vapour and should only last a certain amount of time .

i do not ever remember seeing the effects i see now when i was younger even in the same weather conditions

You say "even in the same weather conditions". Mind giving us some insight as to how you can, at ANY time, see what the weather conditions are at 30k feet by just looking up? Please do keep in mind that the weather conditions on the ground have absolutely nothing to do with the conditions up there.

i have figured that out while parachuting and studying the weather patterns .maybe we should go back to the old engines if it will keep the sky clear

reply to post by Phage


Yes there is more traffic, but as more aircraft are switching to more efficient engines, we're seeing more contrails, and more persistence.

Aircraft cause contrails when flying in an atmosphere colder than a threshold temperature which depends on the overall efficiency η of propulsion of the aircraft/engine combination. Higher η causes contrails at higher ambient temperatures and over a larger range of flight altitudes. The ratio of temperature increase relative to moisture increase in engine plumes is lower for engines with higher η . Thermodynamic arguments are given for this fact and measurements and observations are reported which support the validity of the given criterion. The measurements include contrail observations for identified aircraft flying at ambient temperature and humidity conditions measured with high precision in-situ instruments, measurements of the temperature and humidity increases in an aircraft exhaust plume, and an observation of contrail formation behind two different four-engine jet aircraft with different engines flying wing by wing. The observations show that an altitude range exists in which the aircraft with high efficiency causes contrails while the other aircraft with lower efficiency causes none. Aircraft with more efficient propulsion cause contrails more frequently. The climatic impact depends on the relative importance of increased contrail frequency and reduced carbon dioxide emissions for increased efficiency, and on other parameters, and has not yet been quantified.

www.sciencedirect.com...

A great example is the picture of the Airbus with high bypass turbofans with a contrail behind it, and the 707 with low bypass turbofans without, both flying side by side at the same altitude. More efficient engines leads to more contrails, and contrails that persist more. Yes, the humidity is the cause, but the engines are producing contrails at altitudes that low bypass turbofans don't produce them at.

reply to post by WonderBoi


Routes change with seasons. People don't fly to some destinations in the summer, so there are fewer flights there. When it cools down in one place, they start flying there more, so more flights. It also depends on the winds. If the winds are favorable for a more direct route, then they'll take that route. When the winds change, they go back to the Circle Route.

reply to post by Zaphod58

High bypass engines will produce contrails at higher ambient temperatures (and lower relative humidity) than earlier jet engines so contrails will be produced by them more frequently.

However, persistence is determined only by ambient conditions. If the air is not saturated a contrail will not persist. It cannot, because the ice crystals will sublimate.

Originally posted by Phage
reply to post by WonderBoi

 

You don't usually notice planes 7 miles overhead unless they are producing a contrail.

But generally speaking contrails of any sort are less likely to form in the summer. Not surprisingly, we hear less about them on ATS at this time of year.
www.abovetopsecret.com...

edit on 7/24/2013 by Phage because: (no reason given)

it is the only time we get to see them in the u.k phage as the 200 + days off rain . when i was young they were gone in minutes the trails now they hang around all day and i am nowhere near airports

reply to post by geobro

it is the only time we get to see them in the u.k phage as the 200 + days off rain

Well yes, if there is a low cloud cover you won't see contrails.

when i was young they were gone in minutes the trails now they hang around all day and i am nowhere near airports

Your memories vary from those of many others (as well as historical records, images, and videos).
You won't see contrails from aircraft inbound or outbound from a local airport. They aren't high enough. You will see contrails from aircraft which are overflying your location.


From 1919:

The second German sighting occurred on May 9, 1919, when a pilot flying over Berlin at about 26,000 feet noticed the generation of a cloud stream that extended for about forty miles behind his plane. This stream eventually spread out to form a cloud layer that was about 3,000 feet thick. The pilot saw a similar phenomenon two days later.

www.questia.com...

From 1940:

A few months later I witnessed the Battle of Britain taking place over my head in the July, August and September 1940. Being in SE London we had a grandstand view of the titanic struggle going on day aftr day with the intricate patterns of the contrails the most evident witness to the dog fights taking place.

www.bbc.co.uk... Short contrails do not produce intricate patterns.

1944:

So an airplane at great heights leaves behind it, stretching for endless miles, a visible "wake" composed of ice particles so tiny that they do not fall as snow but remain suspended in the air.

Source

From 1947:

Photo taken by Jerry Cole, combat aerialphotographer in the 390th Bomb Group at Framlingham Air Base in England. He is looking for a print from the original negative he shot around January 1944 or before. It shows contrails of P-47's crossing each other in the background and a B-17 in the foreground.

scoutbird.tripod.com...


From 1968:

Daily, for example, hundreds of jet planes crisscross the nation or great parts of it, often leaving fluffy contrails of water vapor, manmade clouds, as a signature of their passage.

Some contrails soon dissapate. Others turn into or are soon followed by high cirruse clouds that can and do influence the earth's heat balance with the sun.

news.google.com...,2068835&dq=contrails+cirrus&hl=en





From 1970:

The spreading out of jet contrails into extensive cirrus sheets is a familiar sight. Often, when persistent conditions exist from 25,000 to 40,000ft, several long contrails increase in number and gradually merge into an almost solid interlaced sheet.

journals.ametsoc.org...

Henry Wadsworth Hinkle, hired man down on the farm with Uncle Clarence and Aunt Martha, looked skyward a few days ago and was awed by the multiplicity of "vapor trails," as he called them. That's the old name. Now they are called contrails-short for condensation trails-resulting from the condensation of heat flowing from high-flying jet engines.

Source

A 43-year-old novice sailor said today that he followed jet contrails over the Atlantic to help him navigate after his sextant was smashed six days out of Pymouth, England.

Source He didn't follow jets, he followed contrails. You can't follow a short contrail.

1972:

Then there is the matter of cloudiness. The familiar contrails often left by high-flying planes might persist for a long time under some conditions.

Source

From 1973:

Often, after several clear days, high flying jets begin leaving condensation trails in the sky. These "contrails" are the result of the condensation of water vapor that accompanies engine combustion at high altitudes.

Source

He occasionally looked out the window at the earth and noted geographical locations. "We're coming over Europe and I've never seen so many jet plane contrails in my life," he reported

[url=http://news.google.com/newspapers?id=VZcyAAAAIBAJ&sjid=rOcFAAAAIBAJ&pg=6454,31176

Originally posted by Zaphod58
reply to post by WonderBoi

 

Routes change with seasons. People don't fly to some destinations in the summer, so there are fewer flights there. When it cools down in one place, they start flying there more, so more flights. It also depends on the winds. If the winds are favorable for a more direct route, then they'll take that route. When the winds change, they go back to the Circle Route.

The "circle route", or more properly, "Great Circle Route", IS the most direct route. It only looks curved as a result of trying to portray a spherical surface on a flat 2 dimensional map. Which is why, when I was ferrying F-4s from St. Louis to Saigon or Danang, the direct course went near Alaska.

reply to post by F4guy


It is, but you see flights changing that route for whatever reason. Such as Aeroflot 150 I think it was, when everyone freaked out thinking Snowden was on board. There was turbulence up near Greenland, and the winds were right for them to go on a straight line course out of Europe, so they did. That was what I was talking about, not that it was shorter, but that it was more direct on the map.

Originally posted by Alda1981

Originally posted by F4guy

Originally posted by Alda1981
thought contrails disolved after a period of time. small period of time.

Contrails don't dissolve." They are ice crystals which undergo a phase change. It's called "sublimation" where ice transitions directly to water vapor, without changing to a liquid first. It doesn't melt and then evaporate - it goes directly from solid to gas.
The rate of sublimation depends on a large number of factors. The most important is the ambient vapor pressure. Another factor is the size of the ice particle, or more correctly, the surface area of the sublimating solid. Another factor is whether there is any diffusion resistance caused by vapor cloud density at the phase interface. The exact formulas for determining sublimation rate can be found at link.springer.com...-1. I'll leave it to you to do the math

I've read in a few different places that contrails may actually have the positive effect of global cooling. Not sure how true that is, or if any actual studies have been done.

Originally posted by RangerMel
I've read in a few different places that contrails may actually have the positive effect of global cooling. Not sure how true that is, or if any actual studies have been done.

Then Sept. 11, 2001 presented a unique opportunity to study what the sky looked like without airplanes and contrails. In the wake of the 9-11 terrorist attacks, the FAA prohibited commercial aviation over the United States for three days. That's when David Travis, an atmospheric scientist at the University of Wisconsin, Whitewater, thought to look at how temperatures might differ at temperature stations around the country. He found that [PDF], for those three days, the average range between highs and lows at more than 4,000 weather stations across the US was 1 degree C wider than normal. In other words, contrails seemed to raise nighttime temperatures and lower daytimes ones. But the real effect was in daytime highs, which were much higher. That would seem to indicate that, contrary to prevailing thinking, contrails might have a net cooling effect.

Link to source

They have, and they apparently do.

hi all.
filmed this last night in southern england.
never seen anything like it before.
any thoughts?
youtu.be...

reply to post by swimswam


Video isn't working for me.