[lightarrow (OP)]

http://www.knbc.com/video/9265818/detail.html

http://en.wikipedia.org/wiki/Chemtrail_conspiracy_theory

[another_someone]

The conspiracy theories, at least in their present form, are not at all convincing.

If someone were trying to deploy high altitude chemical experiments, one would expect that they would wish to observe them in a wide range of environments, and not simply deploy them over and over again in the same environment.

It also would seem unlikely that they would base such experiments from an exclusively military airfield.

If there is anything unusual in these contrails, then the kind of experiments that would seem more plausible would be in the use of exotic fuels to power exotic jet engines; but I do not see weather manipulation as being the kind of experiment that would be performed in the way suggested by these conspiracy theorists.

[lyner]

There will be air traffic records to provide information about what sort of craft are in an area at a given time. Are these patterns made by many different planes? Were they all on long range military 'spoof' flights just to camouflage the operation? Too expensive, unless they were commercial flights. Who coordinates it all and keeps it secret? Or are the offending patterns made by one plane, zig-zagging about the sky? That would be very noticeable from the ground. Any evidence of that?
 
The conspiracy idea is about as likely as MI5 arranging a cleverly choreographed motor accident in a French underpass.
Let's look for a more Scientific explanation.

[rosalind dna]

yes it's about as likely as the MI5 changing the vapour/condensation trails that come out of the commercial planes
like the ones that are stuck at Heathrow's Terminal 5.

http://en.wikipedia.org/wiki/Condensation
http://en.wikipedia.org/wiki/Contrail

[paul.fr]

This

Skeptical groups, including the Committee for Skeptical Inquiry, assert that contrails normally exhibit a wide variation in appearance and that the descriptions and photographs of chemtrails are consistent with those of ordinary contrails

Is correct, there is nothing out of the ordinary in the contrails pictured in the wiki article. As far as the conspiracy theories go, well may be. Hands up all of those who think the US will abide by any signature on arms and weapons treaties.

The US have used the weather as a weapon before, during the vietnam war. In fact the US are one of the signatories on ENMOD,  the convention on the prohibition of military or any other hostile use of environmental modification techniques...ENMOD, much quicker to spell.

yet, just 12 years ago the clinton administration  began looking into using the weather as a military tool, try googling "weather as a force multiplier: owning the weather in 2025"

So the conspiracy "nutters" may have a valid claim, or not.

[lightarrow (OP)]

Nasa definitions of contrails:

"Contrails are always made of ice particles, due to the very cold temperatures at high altitude."

"Contrails are man-made clouds that only form at very high altitudes (usually above 8 km) where the air is extremely cold (less than –40°C)."

"Contrails only form at very high altitudes (usually above 8 km) where the air is extremely cold (less than -40 degrees C) "

"Contrails are human-induced clouds that only form at very high altitudes (usually above 8 km - about 26,000 ft) where the air is extremely cold (less than -40 ºC). Because of this, contrails form not when an airplane is taking off or landing, but while it is at cruise altitude."

"Contrails form in the upper portion of the troposphere and in the lower stratosphere where jet aircraft normally fly, generally between about 8 and 12 km altitude (~26,000 to 39,000 feet)."

Do the above definitions apply to all observed trails?

What is this airplane?
http://airlineworld.wordpress.com/2008/03/10/white-plane-at-bratislava/

What are these trails?
http://www.sciechimiche.org/scie_chimiche/images/stories/ChemBlog2008/20080412.jpg
http://www.flickr.com/photos/21627873@N06/2419342462/

[paul.fr]

Do the above definitions apply to all observed trails?

Aside from those few points from NASA, i suppose we should state what a contrail is. A contrail is the condensation trail that is left behind by a passing jet plane, they form when hot, humid air from jets exhaust mixes with the surrounding environmental air of lower vapor pressure and lower temperature.

This mixing occurs directly behind the plane due to turbulence generated by the engine. The contrail is only then visable only if condensation occurs, and even then it is only visable over a time period that is proportional to the amount of humidity already in the atmosphere.
If the atmosphere is dry, then the contrails don't last too long. If the atmosphere is wetter (more condensed) then the trails can last for hours. You can also have a situation where the plane will fly through sections of the atmosphere that have vastly different levels of condensation, this gives you a trail that is fragmented, sort of like looking at the dots and dashes of morse code.


Cloud and contrail watching / observations can and are used as weather predictors. If you have days when the contrails quickly evaporate or don't form at all, you can predict continuing good weather. On the other hand, contrails that persist then this indicates that changeable weather is expected. The way they spread across the sky will also give indications about the wind speed and direction.

I suppose it may be worth mentioning "contrails from ships", these are more generally called ship tracks.
http://en.wikipedia.org/wiki/Ship_tracks
Although, none of the pictures look like they were made by ships, the above link is still worth reading. So is this one, about contrails. http://cimss.ssec.wisc.edu/wxwise/class/contrail.html

So what has all of the above got to do with the question? Well...a bit of background and information as to how contrails form helps make an informed opinion.

What is this airplane?
http://airlineworld.wordpress.com/2008/03/10/white-plane-at-bratislava/

I have no idea! But if i was prone to conspiracy theories, i would rather go with black flights with the passenger being some terrorist prisoner or another. Did they call these rendition flights?

What are these trails?
http://www.sciechimiche.org/scie_chimiche/images/stories/ChemBlog2008/20080412.jpg
http://www.flickr.com/photos/21627873@N06/2419342462/

The first photo is rather strange, it looks like a childs streamer that has been taken by the wind. I offer no opinion as it is hard to gauge height and perspective in the photo.

The second photo looks like standard examples of contrails, nothing out of the ordinary.