Jenn Stroud Rossmann, an assistant professor of engineering at Harvey Mudd College, provides this explanation:
Jets leave white trails, or contrails, in their wakes for the same reason you can sometimes see your breath. The hot, humid exhaust from jet engines mixes with the atmosphere, which at high altitude is of much lower vapor pressure and temperature than the exhaust gas. The water vapor contained in the jet exhaust condenses and may freeze, and this mixing process forms a cloud very similar to the one your hot breath makes on a cold day.
Jet engine exhaust contains carbon dioxide, oxides of sulfur and nitrogen, unburned fuel, soot and metal particles, as well as water vapor. The soot provides condensation sites for the water vapor. Any particles present in the air provide additional sites.
Depending on a plane¿s altitude, and the temperature and humidity of the atmosphere, contrails may vary in their thickness, extent and duration. The nature and persistence of jet contrails can be used to predict the weather. A thin, short-lived contrail indicates low-humidity air at high altitude, a sign of fair weather, whereas a thick, long-lasting contrail reflects humid air at high altitudes and can be an early indicator of a storm.
The mixing gases contained in the contrail rotate with respect to the ambient air. These regions of rotating flow are called vortices. (Any sharp surface, such as the tip of a wing, can cause vortical flow in its wake if it is sufficiently large or the flow is sufficiently fast.) On occasion, these trailing vortices may interact with one another.
 Image: NASA A CONTRAIL left behind a jet aircraft. |
In one well-known example of this fact, the Crow Instability causes the vortices to develop symmetric sinusoidal oscillations and eventually to merge and form vortex rings behind the jet. This instability can be triggered by turbulence in the surrounding air or by local variation in air temperature or density, which may itself be the result of the stratification of the atmosphere. When the contrails are visible and strong, it is possible to see the white streaks become wavy and then leave rings floating high in the sky, like smoke rings from a giant cigar.
Recent research has suggested that the ice clouds contained in contrails cause greenhouse effects and contribute to global warming as part of the insulating blanket of moisture and gases in the atmosphere. Researchers in this area seized on the opportunity presented on September 11 and 12 over the U.S. The complete cessation of commercial air traffic offered a control sky without contrails for use in quantifying the environmental effects of contrails.
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13 Comments
Add CommentI kills me to no end that some actually believe it is the government spraying chemicals into the atmosphere.
Reply | Report Abuse | Link to thisWhy do planes go back and forth every morning over the sky of Oceanside,Ca.92054 leaving so many contrails over the sky that it blankets the sky and blocks the sun from the ground.
Reply | Report Abuse | Link to thisWhy do planes leave so many contrails in the sky above Oceanside,Ca.92054 every morning.
Reply | Report Abuse | Link to thisI have been trying to find the answer to this for years: when a plane flying at, say, 30,000 ft. leaves a contrai, does the contrail stay at that height or does it gradually sink lower as it spreads and disipates?
Reply | Report Abuse | Link to thisi have done my own research since the 70's I have seen my breath in the cold air, it doesnt last long. I have seen crop duster go over corn fields and fog the road when im driving. I have been a trucker driver for 15 years and been all over the us I have seen these jets over populated cities in masses, it is my judgment when i see one jet with a trail maybe 100 from the jet and another going from sunrise to sun set, And then another crosses the same trail that the other jet left, and have sat there and watched for hours and see them creat clouds. that stay their all day. please explain to me how that is the same thing as breathing in the cold.
Reply | Report Abuse | Link to thiscstrok: The analogy to it being like fog created by your breath has only to do with the initial creation of the contrail. Your breath creates fog when you breath out in cold temperatures because your breath contains a far greater concentration of moisture based on its warmth than can be contained by cold air. As your breath air is chilled by the outside environment, the moisture condenses to form your fog breath. However, the small amount you exhale is readily dissipated in the environment, and the small additional amount of water you add easily dissolved in the air that is only slightly colder than your breath.
Reply | Report Abuse | Link to thisThe contrail dumps a far greater amount of moisture into a much colder environment that cannot readily absorb as much water as rapidly. It sometimes does - contrails sometimes don't appear or dissipate rapidly. Persistent contrails result when there is enough moisture at altitude that the contrail vapor freezes and forms a cloud that will persist just as any other cloud. You could duplicate the same effect with your breath if you were able to exhale the same volume of water vapor as emitted by jet engines. And even then, the air at ground level is much warmer (even if freezing) than air aloft so can absorb far more water vapor than air aloft. To duplicate that contrail, you would probably have to exhale far more water vapor than the jet engine since you start with a big disadvantage in trying to create a persistent cloud, and that is the much greater volume of water vapor that can be absorbed by air at ground level.
I live in San Francisco CA and I too have been observing these trails. Earlier today the sky was crystal clear but then these few planes left these trails that became clouds, or more like white sheets, within a few hours. I was curious to why only some planes were leaving these trails and not the majority. I thought that maybe it was the type of plane but I don't see why that would be the case since all planes have exhaust. The airport is close so I thought maybe the planes turn off their engines, or whatever, when they are getting ready to land... I also thought about the altitude of the plane as a factor but then noticed planes higher and lower (or so they appeared) then the trail producing plane, and their trails were short, both in length and time lived. The planes leaving the trails all seemed to be at the same altitude. I watched other planes fly directly through these white trails, as well as above and below them, and again they did not leave a trail like the ones I curiously observed. Air traffic was very busy today so it is a good day to observe this phenomena. All day these planes that looked so similar left these white trails while others at the same time were not. I could see one plane that flew over directly over head exceptionally well. It, like the few others, left the thick white cloud but at first did not. It left a short trail but then, as if it turned on its boosters or second engine, it started leaving two thick white trails. I could still see that short trail that I initially noticed and it remained short while the two white trails stayed in the air for hours while dissipating to cover the sky. Since the trail producing planes were all so similar looking, I thought it must be the type of plane or jet that just releases more exhaust but to quote the article, "Depending on a plane�s altitude, and the temperature and humidity of the atmosphere, contrails may vary in their thickness, extent and duration.", it seems that all the planes at that same altitude as the trail producers should be leaving some trail, otherwise there is something to be said about the regulations and enforcement of how much exhaust planes are permitted to produce, assuming the cause of trail is the amount of exhaust. Please explain to me, considering all the variances I tried to convey, why this is occurring only with specific air-crafts. This article, although informing, does not fully explain what I'm witnessing.
Reply | Report Abuse | Link to thisI can NOT believe how gullible you people are and naive. Do you actually believe these trails are left from condensation (like your breath on a cold day)
Reply | Report Abuse | Link to thisThese are chemicals being sprayed into the stratosphere. Do you ever wonder why we no longer have blue skies, but rather white skies. And its not cirrus clouds. These chemtrails are being sprayed from horizon to horizon and then enlarge over the coarse of the day. They are filled with aluminum and barium. The government are using these trails to depopulate and to monopolize farming, IE-producing aluminum resisting seeds so that organic farming can no longer survive. The soils are poisoned by the aluminum being sprayed. Coconut trees in Hawaii are dying on an organic farming site.
Watch the movie, What in the world are they spraying on us?
iggibtful you need to research before you jump onto the conspiracy bandwagon...this "study" was debunked 2 years ago:
Reply | Report Abuse | Link to thishttp://contrailscience.com/what-in-the-world-are-they-spraying/
why don't these trails get left when an airplane is landing or taking off in temperatures below zero??
Reply | Report Abuse | Link to thisThe government has admitted to spraying chemtrails in the air in the past. Why wouldn't they did it today? whether or not its harmful is another question.
Reply | Report Abuse | Link to thisHahahaha! Nice piece of propaganda. Everyone on here saying that "chemtrails" have been debunked need to REALLY have their head examined. Lets be real here, persistent contrails do NOT expand for hours over the course of a whole day and fill the sky with murky haze. I've personally been documenting these for years and in California they start in the fall and continue till spring. There are a few rare days in the winter where you won't see one trail in the sky. Then the next day the sky will be filled with them. No difference in weather pattern or temperature, so why some days we see them and some we don't. Are there no planes flying on those days? Seriously, I've been waiting for years for someone to tell me the logic behind their "debunking". We all better wake up before the ability to grow food on our own is lost and the fields and water ways are poisoned beyond repair.
Reply | Report Abuse | Link to thisHahahaha! Nice piece of propaganda. Everyone on here saying that "chemtrails" have been debunked need to REALLY have their head examined. Lets be real here, persistent contrails do NOT expand for hours over the course of a whole day and fill the sky with murky haze. I've personally been documenting these for years and in California they start in the fall and continue till spring. There are a few rare days in the winter where you won't see one trail in the sky. Then the next day the sky will be filled with them. No difference in weather pattern or temperature, so why some days we see them and some we don't. Are there no planes flying on those days? Seriously, I've been waiting for years for someone to tell me the logic behind their "debunking". We all better wake up before the ability to grow food on our own is lost and the fields and water ways are poisoned beyond repair.
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