# How long contrails can last, sources, wikipedia

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#### Unregistered

##### Guest
Once again, Your showing photos and short videos....how long are these contrails staying around ?
2 hours is maximum for a contrail to stay there. According to Wikipedia and other source websites.
you can't prove how long they have been in the sky in those videos and pictures. Thanks next!

#### Mick West

Staff member
Once again, Your showing photos and short videos....how long are these contrails staying around ?
2 hours is maximum for a contrail to stay there. According to Wikipedia and other source websites.
you can't prove how long they have been in the sky in those videos and pictures. Thanks next!

What source says 2 hours max?

#### SR1419

##### Senior Member.
Once again, Your showing photos and short videos....how long are these contrails staying around ?
2 hours is maximum for a contrail to stay there. According to Wikipedia and other source websites.
you can't prove how long they have been in the sky in those videos and pictures. Thanks next!

Are these any different than the supposed "chemtrail" videos and pictures that litter the internet?

Do you watch 2-hour long "chemtrail" videos?

#### FreiZeitGeist

##### Senior Member.
2 hours is maximum for a contrail to stay there. According to Wikipedia and other source websites.
you can't prove how long they have been in the sky in those videos and pictures. Thanks next!

From the Book "A Color Guide to clouds" from Richard Scorer & Harry Wexler, 1963

"...often it may last for several hours"

... and another from 1972: Richard Scorer - "Cloud of the worlds"

"may last for many hours"

and German Wikipedia says "Die Lebenszeit kann mehrere Stunden betragen, in einem Fall war ein einzelner Kondensstreifen über 17 Stunden auf einem Satellitenbild zu erkennen."

Translation: The Lifetime (of a contrail) can takes several hours. One times a single contrail was visible for over 17 hours on a satellite picture
http://de.wikipedia.org/wiki/Kondensstreifen

Wikipedia takes this link as source for the 17-hours-contrail: http://www.agu.org/pubs/crossref/1998/97GL03314.shtml

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#### Mick West

Staff member
I'd recently been assuming that the Wiki entry that believers were linking to was just badly written. Turns out that it had been edited to say that contrails only lasted seconds or minutes, which doesn't really tie in with the next sentence about persistent contrails and their effect on global warming. The original text has been restored now.

http://en.wikipedia.org/w/index.php?title=Contrail&diff=526385431&oldid=525574453

Looks like the removal was back in september by an anonymous user, pity nobody noticed it until now.
http://en.wikipedia.org/w/index.php?title=Contrail&diff=511052320&oldid=508766702

#### Pete Tar

##### Senior Member.
Was that a real life disinformation tactic? Like what those who stick to verifiable facts are always being accused of?
These people really have no ethics at all.
Lame. Much lame.

#### Belfrey

##### Senior Member.
Although it does not specify how many hours, I thought I'd share this early (1951) reference I recently found, prepared by Cornell University for the Office of Naval Research: Prediction of Aircraft Condensation Trails: Project Contrails (Final Report).

#### Pete Tar

##### Senior Member.
I think this is the right place for this question - why does a contrail form and disappear quickly?
I was just looking at a plane with a contrail that was about 3-5 lengths of the plane following along and disappearing in motion with the plane.
Does the wake of the plane create a disturbance in temperature or pressure that allows for the trail, which is negated once the wake has settled?

#### Jazzy

##### Closed Account
Was that a real life disinformation tactic? Like what those who stick to verifiable facts are always being accused of?
These people really have no ethics at all.
Lame. Much lame.
The reason why they think the "opposition" uses them is that they can imagine it - and as we know - whatever they imagine must be true. It goes well with their easiness with painfully obviously fraudulent evidence on the basis that at least it's a return blow of some sort, against what they imagine to be insuperable odds.

It is indeed very lame stuff. I'm beginning to believe that any reaction just feeds them. They are true trolls, and if left to their own devices in any respect are too inept to do anything except damage their own case. We should stand back and watch. They're going nowhere.

Ah the above question. Yes it's quite possible for a trail to disappear pretty quickly. Freezing is quick because it happens in the gaseous phase, but sublimation into cold dry air (requiring a further latent heat exchange) is dependent on the surface area alone presented by the ice crystals. There are massively fewer collision opportunities. This somewhat explains the difference between freezing and sublimation speeds.

If the jet engine were firing into the cold vacuum of space (it would have to be a HOTOL), ice crystals could also form, then evaporate (but most steam would escape as a free gas). Pre-existing water vapor pressure at altitude slows this process, and can reverse it.

There must be a loose connection between trail gap length and minimum trail length in the driest conditions, where the visible short trail must be some multiplicand of the trail gap. The short trails I've seen were roughly fifty times as long as their gap.

#### Trailspotter

##### Senior Member.
Although it does not specify how many hours, I thought I'd share this early (1951) reference I recently found, prepared by Cornell University for the Office of Naval Research: Prediction of Aircraft Condensation Trails: Project Contrails (Final Report).

I can add this reference: A case study of the radiative forcing of persistent contrails evolving into contrail-induced cirrus

There is a slideshow on these results at the BBC News site.

#### Mick West

Staff member
I think this is the right place for this question - why does a contrail form and disappear quickly?
I was just looking at a plane with a contrail that was about 3-5 lengths of the plane following along and disappearing in motion with the plane.
Does the wake of the plane create a disturbance in temperature or pressure that allows for the trail, which is negated once the wake has settled?

It's basically the exhaust mixing with ambient air, which happens very quickly.

In the graphs below, the point B is where the exhaust gasses come out of the plane. The point A is the ambient conditions. As the exhaust mixes, it goes from point A to point B. You get the short trails if point A (the final result) is too dry to support contrails, but the mixing line still goes through the region where clouds form.

http://science-edu.larc.nasa.gov/contrail-edu/resources/Contrail_Formation_English.pdf

The longer the mixing line is in the condensation area (labeled "cloud", above), the bigger and more numerous the ice crystals, and the longer it will persist. And if the end result is in ice supersaturated air (labeled "moister air" in the diagram below), then it will persist and grow (accreting more ice) as long as ambient conditions remain ice supersaturated.

The wake does have an effect, but not one that stops a few planes lengths behind the plane. Wake vortices can sometime make extra dense portions of contrails I call "vortex contrails" or "hybrid contrails" which are very thin, and usually break up in a very wiggly manner, with the crow instability.

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