I snapped this a few minutes ago, looking west from Santa Monica:
I snapped this a few minutes ago, looking west from Santa Monica:
It’s been interesting weather here in Los Angeles, as a couple of storm systems have rolled through we’ve had some days of nice looking clouds, and some days with lots of contrails. I snapped this one this morning:
It shows a contrail from the lower left that then turns into a distrail on the upper right, cutting through a layer of clouds.
Either by day or a little after sunset, in fine weather, a little, light, long-drawn cloud is seen, like a long very straight line.
– Aristotle, Meteorologica, 340BC
Not every long straight line in the sky is a contrail. Here Aristotle suggests it’s “a sort of wave-mark in the air”. Basically an isolated row cloud, low on the horizon.
Aristotle’s take on the weather is very interesting. He has quite an extensive section on atmospheric optics – halos, sundogs, etc. Pretty advanced for 2347 years ago.
Some conspiracy theorists think that persistent spreading contrails indicate some kind of deliberate aerial spraying, probably by the government. They speculate as to what could be in these trails, and one of the most common things they claim is barium.
Some people are so obsessed by this idea that they have rainwater tested to see if it has barium in it. They usually find some, and then trumpet this as evidence that their theory is correct.
Unfortunately they are wrong. I’ll explain why, but first, some basic science. Read More
Some people think that persistent spreading contrails are somehow unusual, and are actually something dangerous being deliberately sprayed on the US people by the government, or perhaps for weather control purposes. They call these persistent contrails “chemtrails”.
Some of them are very insistent that this is a practically constant assault, saying the sky is never blue any more, and there are “chemtrails” constantly criss-crossing the sky.
I’ve talked about distrails and hole punch clouds before, but I’ve actually never seen one myself until this morning, when I saw two side by side. It’s quite rare to have this kind of weather condition in Los Angeles. I took a couple of photos at around 7:30AM today, Aug 19th, 2007. Santa Monica ATIS reports the sky is clear now, but Van Nuys reports broken cloud at 18,000 feet and 28,000,which is probably where these are, given they look like they are precipitating ice in artificial cirrus uncinus. The cloud layer that the holes formed in is cirrocumulus.
There was an interesting post over on the New York SkyWatch blog, which raised many of the common questions that people have about various contrail anomalies. I’ve attempted to answer all of the questions here:
Question #1, why [do] jet contrails appear as if the jet engine is being deliberately turned on and off?
It’s because the jet is flying through uneven areas of temperature and humidity. Explained here
Question #2, Explain why jet aircraft are leaving persistent contrails in grid patterns?
Because some jets fly north-south, and some east-west on airways that are several miles wide, and where they cross you get a grid. Winds at altitude blow at around 90mph, and these blow the trails across the sky, increasing the size of the grid.
Question #3, Shouldn’t the entire sky be filled with contrails? Would we ever see any truly blue sky again if all jets left persistent contrails behind?
Sometimes there are a lot of contrails, and they do spread out and cover the sky. Sometimes there are only a few. Sometimes there are none. It depends on the weather. There are only a certain number of jets flying overhead every day. They have to be at the right altitude for contrails to form. In some weather conditions this is limited to only the highest jets, or sometimes just jets in a narrow band of humid air. On very cold humid days you will see a lot of contrails, but no more than the number of jet at altitude.
Question #4, I know that contrails are formed under certain weather conditions and altitudes. However, there are times when conditions do not exist for contrails to persist?
Then they will not persist. The problem here is that it is incredibly difficult to know what the humidity is at a specific time, altitude and location. Humidity measurements are done by sending up a balloon every 12 hours from weather stations 300 miles apart, the balloon can be blown hundreds of miles in a random direction during its ascent. How can you get an accurate local humidity reading at a specific time and place from a balloon reading 6 hours ago and 300 miles away, when humidity can vary enough for contrails to form or not form in as little as half a mile (as you can see from the broken contrails), and humidity can vary by 50% over the course of a day?
Question #5, Certain contrails even look like they are laden with chemicals. You know the ones I mean. The ones that appear to drip by the weight of their own substance, mushrooming along the bottom edge of the trail. C’mon what’s in this stuff. It doesn’t even look like ordinary condensation to me?
They are called “pendules”, as seen in this pre-1991 photo, and described by Schaefer and Day in 1981. When a plane flies through the air at 500mph it creates wake turbulance, which is made up of wake vortices, (whirlpools of air), at regular intervals. These vortices make the contrail clump up in areas of greater and lesser density. In a dense persistent contrail, the vortices will produce the clumping pendules seen in the first photo. If the contrail is thin or not persistent, then they can leave interesting patterns which can resemble smoke rings. The type and visibility of the vortices will depend on the the size, shape and speed of the jet, as well as the turbulence and density of the air it is moving through.
Question #6, Speaking of abnormal, I have seen jets emitting contrails that are dark in appearance. I assumed that it might be the lighting conditions until I saw the black and white contrails side by side – check out this video?
I covered this in the “dark lines” article. It is the lighting conditions, the dark contrail is in shadow, and when you see contrails “side by side”, the lighter contrail could well be ten miles behind (or a mile above) the darker contrail, and so not in shadow.
Question #7, Another interesting aspect to these dark trails is that the material drifts to the ground in clouds that resemble the black smoke from a nearby fire. I have observed this process several times in the fall. I haven’t seen them since the beginning of the year?
Precipitation falling from clouds will look dark if it is in shadow, which is probably will be if the shadow is caused at sunset by a hill or cloud bank.
Question #8, And then there’s the other trails that appear to swallow up other trails and clouds. One of my YouTube videos shows this quite clearly. My first impression was that someone had a HUGE washcloth and scrubbed a portion of the sky. And then I saw jets going through the cloud mass and the contrails that were left created lines in the mass that expanded and left the cloud in sections.
This effect was observed in 1944, it’s basically a distrail, which is the opposite of a contrail, the cloud contains moisture, and the added moisture, particulates and turbulence of the jet passing through makes the amount of moisture in the air too great for it to exist as a cloud, so it precipitates as snow or rain. This wipes away the cloud where the contrail has been. This can also happen with cloud layers that are below the contrail, as precipitation from the contrail falls on the cloud layer. This is also known as “hole punch clouds” and “fallstreak holes“. Distrails can combine with the vortices of question 5, as in the photo on the right.
I hope I’ve answered all these questions. If you feel there is still something unclear, or you have extra questions, then please leave a comment below.
*UPDATE* Some more questions were raised in the comments, and I’ll add them here, with answers.
Question #9, On your website you have a picture of one jet leaving a “chemtrail” with another jet at the same altitude in the background is not leaving one. I have seen jets side by side and one leaving a normal contrail and another leaving a chemtrail?
See this post for a full discussion.
There are two possibilities. either the jets are not at the same altitude, and just look like they are because of the viewing angle, or they have different engines with different exhaust characteristics. The more efficient an engine is, the more likely it is to leave a lasting contrail, as there is more water in the exhaust. The photo on the right shows an Airbus A340 (maiden flight: 1991) on the left, leaving contrails, and a Boeing 707 (maiden flight: 1957) not leaving contrails. Both are flying at 33,000 feet (part of a German test to study contrail formation), but the newer engines of the A340 produce more water vapor.
Questions #10, How do you explain pictures of aircraft spraying chemtrails from ports other than the engines?
It’s an optical illusion. The contrails come from the engines. Engine exhausts contain a lot of water, which (combined with the water in the air), condenses, freezes and causing the contrail. Because it’s hot when it exits the engine, it takes a fraction of a second to condense and freeze (in 40 below temperatures). So it begins to freezes about 100 feet behind the engines, which makes it look like it’s coming from the ends of the tail section. This illusion is stronger on a shorter two-engine plane – look at the inner engines on the picture on the right. Since it’s a four engined 747 (240 foot long), the contrails form before the tail section, but with shorter planes such as a 767-300 (180 foot long) the contrails would be forming about at the tips of the tail section when viewed from below (although they are actually well underneath the tail, as you can see in the close-up).
In very humid conditions, the turbulence caused by the aircraft itself can cause moisture in the air to condense, and hence freeze. This happens in areas of low pressure above the wing, and in the wingtip vortices, so you can get what looks like a solid sheet of contrail from the wing, and thin streamers from the wing tips (and maybe the tail), combined a bit further back with the engine contrails, as in the photo on the right. These low-pressure wing contrails can form at any altitude, given the right humidity, and account for the tales of planes landing “still spraying”.
Question #11, How do you explain scientists testing the fallout and finding aluminum, barium, nano particles, fungus, molds, viruses, etc in the mix?
They did not test contrails, they just tested some stuff they found on the ground, with no indication that it was connected with contrails (it would take several days for aerosolized matter to reach the ground, and by that time it would have been spread hundreds of miles from the original site). Most of the things they claim to have found are things that naturally occur in air and dirt.
Contrails are clouds made from water vapor that condenses then freezes behind a plane engine. Since the engines are on constantly, it seems a bit odd when you see contrails with gaps in them, or even contrails that stop and start. If the engine is pumping out a constant amount of water, then why is the trail not constant? This puzzle is sometimes seized on by people who think that persistent contrails are actually “chemtrails”, or some kind of deliberate spraying operation. Read More
People who think persistent contrails indicate some kind of conspiracy (which they call “chemtrails”), sometime point to the “dark lines” that sometimes accompany contrails. Since they can’t immediately think of why these dark lines should be there, they assume it’s part of the conspiracy. Either there is some kind of “dark chemtrail”, or the plane is projecting a dark beam of some kind of negative energy, or it is following a dark beam.
In reality these “dark lines” or “black beams” are simply various kinds of shadows. There are actually three main kinds of dark line related to contrails.
Where the contrail itself is in shadow and appears dark. This can happen a number of ways. The sun can be low on the horizon and the contrail can be shadowed by a mountain or a thick cloud bank (such as in this video). In rare cases the plane can be flying directly towards the sun, and the contrail will shadow itself. When self-shadowing, the leading edge of the contrail will be brightly lit, with a dark area behind it, such as parts of the contrail above.
The contrail is simply casting a shadow on a layer of cloud beneath it. The cloud layer is thin enough so you can see through it, but it’s visible, so you can see the shadow on it. Theoretically you could cast a shadow on a cloud layer above or behind a contrail, if the sun were low enough, but this would be rather difficult to observe. Most “dark lines” are of this type. There’s an excellent explanation of these shadows over at Atmospheric Optics.
There’s nothing new about such shadows. Here’s some from 1955:
One interesting thing about these shadows is that it frequently looks like the contrail is below the clouds, when it’s actually above them. You can see this illusion in the photo above. The reason this happens is that the white of the thin layer of clouds and the contrail are additively transparent, so they look identical, regardless of which one is in front of the other. The illusion happens because the brain interprets the bluer regions of the cloud as being darker regions in the same plane as the cloud, when they are actually holes in the cloud.The contrail will seem solid white when viewed through the holes, or when it is in front of the holes.
The most interesting type of contrail dark line is when the contrail is lined up with the sun. This produces a slice of shadow through the atmosphere that looks like a dark line when viewed edge-on. It is quite difficult to visualize what is going on since you have to think in three dimensions, and we are accustomed to thinking of shadows as being flat, since they are usually cast on surfaces. You are not seeing a thin dark shadow here, you are actually seeing a huge slab of very faint shadow, but it’s viewed from looking along the edge. Imagine you have a thick sheet of glass. Viewed head on, it’s transparent, but if you look at it from the edge, it seems a lot darker.
The above image is an excellent demonstrating of the fleeting nature of these edge shadows. Two photos taken just a few minutes apart, int the first the camera is more fully in line with the plane of the contrail. In the second the contrail (or the photographer) has moved, and we are viewing the edge shadows from a slight angle which reveals they are made up of two or three segments, caused either by the plane turning slightly, or variations in upper level winds bending the contrail.
Most photos of these odd shadows don’t include the sun. But when they do, you’ll see that the sun is lined up with the contrail (or part of it)
The photo on the right is a rather dramatic illustration of this effect. The “dark line” here is caused by the slab of shadow cast by the portion of the upper part of the exhaust trail of the space shuttle Atlantis that is lined up roughly in a flat plane with the camera and the sun. The sun has just set, so the rays of the sun are almost parallel to the ground, so the upper portion of the plume is casting a long tall shadow through the air towards the horizon. This is viewed edge on from below, and so looks like a dark line. Since it’s a full moon, the sun is directly opposite the moon, so the “shadow” looks like it’s pointing at the moon (if you look closely, you’ll see it continues past the moon). This is particularly dramatic because of the combination of the setting sun and a vertical exhaust trail. With normal contrails, the sun has to be higher in the sky to cast the slab of shadow downwards.
The image above is another great illustration. There are multiple contrails, but only the one that intersects the sun creates the edge shadow. Photo from “Col” on usenet uk.sci.weather.
[UPDATE] This video I shot in my kitchen gives an excellent illustration of these types of shadow.
[Math Warning] It’s a bit difficult to explain these edge shadows (also called volumetric shadows). You can think of them in terms of three dimensional geometry. The contrail is a line in three dimensional space. The camera (or observer) is a point in three dimensional space. The sun is essentially infinitely far away, and so is only really relevant as a directional vector (a vector in three dimensions, where the magnitude is unimportant ). These three quantities are what you need to consider to understand the condition for the edge shadow.
Given the line (contrail) and direction vector (sun) we can form a plane that contains the line, and is parallel to the direction vector. This plane cuts through the contrail, the atmosphere, and intersects the ground. Projecting two end points of the contrail along the plane in the direction of the sun’s vector, we get essentially a two dimensional parallelepiped (although the far edge is not very well defined). This parallelepiped is quite thin (it’s as thick as the contrail), so when viewed from the side, you won’t see much. But when the viewer is in the plane of the parallelepiped – specifically anywhere along the line on the ground formed by the intersection with the plane formed by the contrail and the sun – then they will be viewing the parallelepiped from edge-on, and so it will seem to be a dark line that intersects the contrail.
Since only the portion of the contrail that is roughly within this plane is contributing to the shadow, there may be other potions of the contrail that are not in the the plane, and hence do not seem to be casting a shadow. In fact they are, but since it is in a different plane, they are not visible unless the viewer was to move to a new position. This can be seen in the two photos above. In one it looks as if the plane was following a dark line, and then veered off. In the Shuttle photo, the highest portion of the trail, although brightly illuminated, is not contributing to the visible shadow. However a viewer in another location may have been able to see a different edge shadow trailing from this upper portion.
[Update] I found a useful video of an contrail edge shadow (or “volumetric” shadow, described above):
It’s all in one shot, which is great, as you can see how the various misinterpretations can arise. It starts out with a shot of a black line across the sky, with no visible reason for it being there. The sun is obscure by the house on the right.
The cameraman then zooms in in the dark line, and we see a contrail being formed along it. It looks like the plane is following the dark line, or somehow projecting a beam of dark energy in front of it!
Then the cameraman walks around the house, and we see the source of the dark line – the contrail is EXACTLY lined up with the setting sun, and is simply casting a volumetric shadow which the cameraman is lined up with. The shadow is accented as the suns rays are nearly parallel to the contrail. Here I’ve stitched some frames together so you can see this. I encourage you to examine the video to confirm this.
[Update 2] Check out this video of the Space Shuttle launch, a dark shadow forms in the last 30 seconds:
[Update 3] Crepuscular rays are parallel, but usually don’t look it. This is partly why the contrail edge shadows are not recognized as the same type of thing.
view of crepuscular rays from space:
How high are those contrails? That’s a very important issue if you are investigating the science of contrail formation. I’ve been thinking for a while that a good method might be to take photos at a plane at a known focal length on a digital camera, and then by measuring the pixels of a known dimension of the plane (the length, or the wingspan), then you could calculate the height.
So I was delighted to find that someone had already done just this, in an article titled: “Points to Ponder: Calculate the altitude of aircraft using a digital camera” (http://archive.is/kUvsB). They had worked out the math, and even given a little calculator.
Given this photo, which is an enlargement of the inset:
One of the more pervasive myths regarding “chemtrails” is that 2008 presidential hopeful Dennis Kuchinich tried to have them banned by an act of congress, but was pressured by the government to modify the act to remove the mention of “chemtrails”.
So what really happened? In a nutshell, Kucinich did not write the bill (or read it, until too late), the focus of the bill is nothing to do with chemtrails, it was written by UFO enthusiasts Alfred Webre and Carol Rosin, who were trying to:
They listed a bunch of weird weapons, including mind control, tectonic weapons and (very briefly) chemtrails. The bill was re-written several time in less unusual language to give it chance of passing, but ultimately fizzled in committee. Read More
I like these contrails from the movie Cars:
They look a little odd at first, but if you look closely (click on the image to expand it) you can see they are actually tire tracks. Here’s some more pics, from a site that thinks the government had these added to the movie to brainwash children into not noticing them when they grow up. Read More
Some people believe that the government is spraying something into the air, and this creates unsual looking contrails. They call these “chemtrails”. Now, there is no real evidence that “chemtrails” are real, but there are several myths on the internet about “chemtrails”. All these myths can very easily be shown to be false, and I’ve gathered the most popular myths here as a little time-saver for the person who has encountered “chemtrails” for the first time.
Myth #1 – Normal contrails don’t last very long, but “chemtrails” last for hours and sometimes spread out.
False – Contrails fade away, or persist, or even spread out to cover the sky, depending on the weather conditions. you can confirm this by looking in an encyclopedia. such as the Encyclopædia Britannica
[Contrails] may last for several hours. The trail may be distorted by the winds, and sometimes it spreads outwards to form a layer of cirrus cloud.
For more info on this myth, read “Persisting and Spreading contrails”
Myth #2 – Contrails have been observed to persist and spread when the humidity was too low, so they must be “chemtrails”
False – Nobody has ever measured low humidity within a persisting contrail. The fact is it is very difficult to measure humidity in a specific region at a specific altitude, at a given time, the best you can do is make a rough prediction. Measurements are made by weather balloons at just a few stations that average 235 miles apart, at 12 hour intervals, and then local predictions are extrapolated from this. The weather balloons can drift as much as 100 miles in their ascent, so you never know where the measurements are coming from. Humidity can vary by as much as 80% in a 12 hour period, and vary by similar amount over just a few miles. The fact that the contrail is spreading is actually a far more accurate indicator of high humidity than the available humidity predictions. NASAs own experiments (right) show persisting contrails over a large range of calculated humidities, even down to 10%.
Myth #3 – Long lasting contrails have appeared in “parallel lines”, “grid” and “X” formations, which are not normal, so must be “chemtrails.
False. Well, the last bit is false. Yes, contrails make all kinds of patterns in the sky, simply because there are a lot of planes flying overhead, and they fly in all directions. This is pretty much a function of where you live, and the prevailing winds. For example, if you live the Willamette Valley, Oregon, the overflying planes are nearly all North/South, so you’ll get parallel lines. If you live live in more central place, like North Texas, you’ll get planes flying overhead in every direction, so you will get “X” patterns (and “H” and “grids”). If there’s enough wind, and the trails last long enough, then the grid might spread out to cover the sky.
Myth #4 – A bill to ban chemtrails was introduced into congress by Dennis Kucinich, but quickly had chemtrails edited out.
False – HR 2977 was written by a bunch of UFO enthusiasts intent on exposing a conspiracy to suppress alien technology. Dennis Kucinich did not write the bill, he not know what chemtrails were, and when he found out, he distanced himself from that language. The bill was re-written in order that it might pass. See the full article: Kucinich, Chemtrails and HR 2977.
Myth #5 – Public Law 105-85 gives the military permission to experiment with chemical and biological weapons on humans, without their consent
False – 105-85, Sec. 1078, actually prevents experiments except for peaceful purposes, and those can only be performed if informed consent is obtained from each test subject. It’s basically the same procedure as for human drug trials.
Those myths are really the basis of the “chemtrail” conspiracy theory. There is more, of course, like the halos and sun-dogs that you sometimes see (normal atmospheric optical effects), the dark lines (shadows of varying types), the stuff on the ground (unconnected). But these things really get to the heart of 99% of the chemtrail argument. After they are dispensed with, the theory holds about as much water as alien mind-control implants.
Let me know if you’ve got something else you’d like investigating, and I might add it here.
Just leave a comment below.
The opposite of a contrail is a “distrail”. When a jet flies through a high cloud then various factors to do with the passage of the jet are sufficient to trigger precipitation in the cloud, leaving holes or trails. The precipitation can spread outwards quite a distance.
This is a satellite image over Texas. Holes form when the plane is climbing or descending through the cloud. The longer trails form when a plane flies at about cloud height for a while.
Here’s another example from North Texas, and a picture of what these hole shaped distrails look like from below.
How many people are interested in chemtrails? Not very many I suspect. But how to measure them? One way is to see how popular they are on the internet. You could measure how many web pages mention “chemtrails”, but that could give a distorted picture, as the people who believe in chemtrails might tend to be much more likely to post their beliefs on the internet. Lots of people knit, for example, but only a tiny fraction of them make knitting web sites.
We could count blog posts, but that has similar problems, as people who believe in conspiracy theories seem quite keen on spreading those theories, and so are more likely to blog about them
The best way that occurred to me was to measure search terms. Simply see how many people were googling for “chemtrails” vs. other words. In this Googlified world, if people are interested in something then they google it.
Here’s my raw data:
|Google Blogs||Google Images||Video||News||Scholar||Pages/Posts||Groutability 2006|
The columns are fairly self explanatory. They are the number of results returned by google for web, blogs, images, videos, news and scholar. The pages/posts column is the ratio of total web pages to blog posts. The “groutability” column is the ratio search volume for that word to the search volume of “grouting”. I chose grouting as it seemed like a thing people would be searching for at a fairly constant volume, but not too much.
I chose search terms that had a similar result to chemtrails. I also added some outliers, that were very popular, or very unpopular, mostly activities practiced only by a few (like reborning). I included “morgellons”, as it seems like the most similar thing I could find with a distinct name.
You can look at the numbers and draw your own conclusions. Chemtrails has more results than “killer bees”, but less than “bboy” ( a type of athletic break-dancing). It has vastly less than knitting and archery. But a lot more than “reborning” (making realistic baby dolls).
But how many people are interested in chemtrails? Well, there are about 30,000,000 knitters in the country, and 600,000 blog results. So given the 4828 blogs results for chemtrails, that would indicate 241,000 people have some interest in chemtrails. But, like I said, it’s not easy to accurately extrapolate. If you could extrapolate from blogs, you could say there are three times as many chemtrailers as there are vexillologists (flag enthusiasts).
Or you could say: a lot more people are interested in Parkour than are interested in chemtrails.
[Update] Chemtrails on Usenet (archived on Google Groups), were only mentioned in 1999. Here are the year-to-year search results for the word “chemtrails”. There are NO results prior to 1999
1999 – 1070
2000 – 2050
2001 – 2810
2002 – 2250
2003 – 2060
2004 – 2100
2005 – 1570
2006 – 2450
2007 – 2230
Do contrails sometimes persist and spread out?
Yes, see the Encyclopædia Britannica article on vapour trails (contrails):
Contrail, streamer of cloud sometimes observed behind an airplane flying in clear, cold, humid air. It forms upon condensation of the water vapour produced by the combustion of fuel in the airplane engines. When the ambient relative humidity is high, the resulting ice-crystal plume may last for several hours. The trail may be distorted by the winds, and sometimes it spreads outwards to form a layer of cirrus cloud.
vapour trail. (2007). In Encyclopædia Britannica.Retrieved May 4, 2007,from Encyclopædia Britannica Online: http://www.britannica.com/eb/article-9074829
(The above quote is from the current EB. However, a Google books search dates the inclusion on the EB back to 1983)
Also see “A Field Guide to the Atmosphere“, by Schaefer and Day, 1981:
“Sometimes [contrails] are ephemeral and dissipate as quickly as they form; other times they persist and grow wide enough to cover a substantial portion of the sky with a sheet of cirrostratus“ (Page 137)
Are spreading contrails a relatively new thing?
No, it has been exactly the same for decades, the only change has been the size of jet engines (producing bigger contrails), engine technology (burning fuel more efficiently in high bypass jet engines creates cooler exhaust which is more likely to condense before it mixes with the surrounding air) and the amount of air traffic (producing more contrails). Spreading contrails have been mentioned consistently through the history of aviation, including in the popular press. Like Sports Illustrated , Nov 6th 1989:
Now, late in the afternoon, the hatchery explored and the fishing over for the day, Crooks points to the sky. Blue all day, it has now turned hazy. “Contrails,” he says. “The haze is caused by aircraft contrails that have gotten spread out till they cover the sky. This is a major air route from the East Coast to the West.”
For scientific discussion, see, for example, all these articles on contrails. In particular the one from 1970 titled “Airborne Observations of Contrail Effects on the Thermal Radiation Budget”
The spreading of jet contrails into extensive cirrus sheets is a familiar sight. Often, when persistent contrails exist from 25,000 to 40,000 ft, several long contrails increase in number and gradually merge into an almost solid interlaced sheet.
Contrail development and spreading begins in the morning hours with the start of heavy jet traffic and may extend from horizon to horizon as the air traffic peaks. Fig. 1 is a typical example of midmorning contrails that occured on 17 December 1969 northwest of Boulder. By midafternoon, sky conditions had developed into those shown in Fig. 2 an almost solid contrail sheet reported to average 500 m in depth.
Airborne Observations of Contrail Effects on the Thermal Radiation Budget
Peter M. Kuhn
Journal of the Atmospheric Sciences
Volume 27, Issue 6 (September 1970) pp. 937–942
(Click on any of the images in this article for a larger view)
Then a few years later, in 1975, we have the article : Multiple Contrail Streamers Observed by Radar, which again has photos (taken in 1971) of spreading and persisting contrails, as well as extensive discussion of these observations.
Aircraft contrails begin to streak the normally bright Arizona sky at dawn. Through the day, as air traffic peaks, these contrails gradually merge into and almost solid interlaced sheet of cirrus cloud – an artificial cirrus cloud that is frequently as much as 500 meters deep.
“Within the past few years, the weather bureau has begun to report the trails as actual cloud layers when there are sufficient trails to cover a portion of the sky.”
Here’s a description from 1955:
An extremely persistent con trail might stay in the sky all day
But even earlier, and with a perfect description of what “chemtrail” theorist claim cannot happen comes this account from 1944:
The News, Frederick, MD, March 7, 1944
“Contrails frequently have a tendency to cause a complete overcast and cause rain. In Idaho I have seen contrails formed in a perfectly clear sky and four hours later a complete overcast resulted“
And from the book “Flight To Arras” by Antoine de Saint Exupery, written in 1942 about a military mission in 1940:
The German on the ground knows us by the pearly white scarf which every plane flying at high altitude trails behind like a bridal veil. The disturbance created by our meteoric flight crystallizes the watery vapor in the atmosphere. We unwind behind us a cirrus of icicles. If the atmospheric conditions are favorable to the formation of clouds, our wake will thicken bit by bit and become an evening cloud over the countryside.
Another from 1958