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Hybrid Contrails

Contrails are generally classified into two types. Exhaust contrails and aerodynamic contrails.

Exhaust contrails are formed by the mixing of the hot humid exhaust of the engines with cold humid surrounding air, creating long streamers of clouds. If the conditions are right then these can persist and spread. These are the most common type of contrail observed.

A typical exhaust contrail

A typical exhaust contrail. There are initially four, one for each engine, then they mix together.


Aerodynamic contrails are  formed by the temporary reduction in pressure of the air moving over the surface of the plane, or in the center of a wake vortex. Reducing the pressure of the air means it can hold less water, so condensation occurs.

An aerodynamic contrail on a landing jet

An aerodynamic contrail on a landing jet – condensation is visible above the wing surfaces, and in the center of the vortices coming from the outside ends of the deployed flaps, but nothing from the engines. This type of contrail is seen in high local humidity, as indicated here by the misty conditions.

I propose a useful new classification for a type of contrail, the Hybrid Contrail, defined as two distinct thin cylindrical portions of an exhaust contrail that have larger ice crystals due to wake vortices. A hybrid contrail is formed in a narrow range of atmospheric conditions, specifically with temperature below -40F, and a relative humidity with respect to ice slightly below 100%. When RHI is below 100% then a contrail that forms will not be persistent, and will eventually sublime away. The low pressure in the wake vortex core allows for a longer period of time in which the mixing air is above 100%, and hence the ice crystals in that portion of the contrail will grow larger and/or more numerous.

The entire evolution of a hybrid contrail can be see in this video. Notice the trail starts out as a large dense regular exhaust contrail, then this fades away leaving the hybrid contrail which separates away from dissipating exhaust contrail, breaking up into loops and segments.

Hybrid contrails will not form when RHI > 100%, as the entire contrail, including the vortex cores, is above the threshold for ice accretion, and so will accrete (gain ice) at the same rate. Hybrid contrails will  not form at values significantly below RHI of 100%, as the relative increase from the vortex core is small, and cannot push the ambient RHI over 100% after initial mixing. Hence hybrid contrails will only form in marginal conditions with RHI only slightly below 100%. A similar narrow range may also apply to temperature.

The resultant region of greater contrail densities will initially be indistinguishable from the exhaust contrail. However as the exhaust contrail sublimates (turns from ice back to water vapor) then the hybrid contrail will be revealed as two thin rope-like regions running along the contrail. The hybrid contrail will sometimes sink away from the exhaust contrail, due to the large size of the ice crystals. Usually the hybrid contrail will persist for a few minutes longer than the exhaust contrail. Since the hybrid contrail is much smaller in cross-section than the exhaust contrail, then the effects of turbulence and crow instability cause the hybrid contrail to twist into loops and curls that often resemble chromosomes.

A hybrid contrail below the parent exhaust contrail. The larger ice crystals in the hybrid contrail have caused it to fall quicker than the Exhaust Contrail, leading to considerable separation, even though they were originally part of the same trail.

A hybrid contrail below the parent exhaust contrail. The larger ice crystals in the hybrid contrail have caused it to fall quicker than the Exhaust Contrail, leading to considerable separation, even though they were originally part of the same trail.


The reason this new classification is needed is that people frequently mistake these hybrid contrails as being regular exhaust contrail, and they cannot understand why these particular contrails loop and twist in such a dramatic and asymmetric manner. In addition hybrid contrails are often spotted within regular exhaust contrails, and this is presented as evidence of something being sprayed within the cover of the contrail. Hybrid contrails also often look very unusual, and this is taken as evidence of some novel propulsion mechanism.

Hybrid contrails often end up looking like a string of chromosome pair. This turbulent flow of the aircraft wake would not be as apparent with the much larger exhaust contrail.

Hybrid contrails often end up looking like a string of loops or chromosome pairs. This looping and twists would be less apparent with the much larger exhaust contrail, as it would simply happen within it. The loops are actually the wake vortices themselves twisting, and as the hybrid contrail exists in the center of the vortex, the effect is much more pronounced.

While I’m suggesting a new classification, this is not in any way a new type of contrail. In fact it has been observed for many decades, such as in the 1972 book: Clouds of the World:

This 1972 book, Clouds of the World, discusses the formation of Hybrid contrails.  But does not give them a particular name.

This 1972 book, Clouds of the World, discusses the formation of Hybrid contrails. But does not give them a particular name.

The full development can be seen here:


Development of a the hybrid portions of a contrail are shown from the initial four separate exhaust contrails, though to just the two hybrid contrails and crow instability breakup.

Development of a the hybrid portions of a contrail are shown from the initial four separate exhaust contrails, through to just the two hybrid contrails and the crow instability breakup. The hybrid contrail is probably sinking below the exhaust contrail, but since it’s viewed in line there’s no visible separation.

In a four engined jet the contribution to the hybrid contrails comes mostly from the outside engines. This is because they are much closer to the ends of the the wings, and so feed almost directly into the vortices. The inner engines contrails are pushed down by the vortex sheet, and are greatly spread out before they might contribute. The following animation shows this initial separation:

The contrails from the inner engines are greatly spread out before they become entrained with the wingtip vortices, the outer engine’s contrails flow into the vortices at a much earlier stage.



27 thoughts on “Hybrid Contrails

  1. siegmund says:

    Hello Mick,

    Your article is very interesting but contains a tiny misunderstanding.
    The appearance and duration of ice plumes are depending on T and RH.
    The most interesting situation is when RH is slightly below 100%:
    The plume is very impressive but is dissipating finally (within 1 min).
    There is a characteristic difference between the two inner and outer plumes:
    Due to slightly higher temperature the inner plumes sublimate earlier,
    whereas the outer persist longer showing two thin cores near the end,
    which disintegrate and totally dissipate (sublimate) eventually.

  2. Seigmund, are you saying that what I’m calling “hybrid contrails” are just the outer two plumes of a four engine jet? Because that would be a pretty big misunderstanding on my part.

    I don’t think that’s it though. Look at the video above, it’s a two engine jet, yet still results in the same dense (hybrid, vortex) trails plus one diffuse (combined exhaust) trail that the four engine jet leaves.

  3. siegmund says:

    To be precise: The plumes of a four engine jet move to different height levels after generation.
    The outer two plumes ascend whereas the inner two descend forming a 3-dimensional structure.
    Moreover the outer plumes are of sharper shape and higher density with an inner core.
    The inner plumes are more diffuse from the beginning and dissipate/sublimate earlier.
    Thus the inner core of the outer plumes will stay longer as thin twin trails.

  4. siegmund says:

    Now a view from the opposite direction where you can see the different plume levels (at 0:22):

  5. Thanks, that certainly makes sense, the inner contrails are entrained in the vortex sheet, and pushed down and spread out, whereas the outer contrails are wrapped around the wake vortices.

    What about the “hybrid” aspect though, sure it’s mostly the outer engines contributing to it here, but the same effect happens with a two engine plane?

    I probably need to clarify the tall image though.

  6. Jeff says:

    Very interesting write-up. If I may add, one more thing which impacts the formation & persistence of the hybrid contrails (visibility of the wingtip vorticies) is the wind environment the plane is flying through. If the 3-D volume wind field is a consistent speed & direction, the air will appear ‘calm’ (uniform) & will allow the long-term persistence of the vorticies. If there is any kind of shear in speed or direction, the air will be turbulent & will tear the vorticies apart before they have a chance to separate from the rest of the contrail formation.

  7. Alexey says:

    Published yesterday on the BBC News site:

    Vortex from plane landing at Heathrow rips off roof

    There is one sentence that sounds confusing: “BAA, which operates Heathrow Airport, says only one in 10,000 flights results in a vortex.”

    I’d think that vortices are formed practically every time, but only a tiny fraction of them are strong enough to cause damage to the buildings on the ground. Am I correct?

  8. Yes, 100% of flights cause vortices, the 1 in 10,000 figure comes from:

    “Less than 0.01 % of flights cause vortex damage”

  9. Anonymous says:

    it absolutely amazes me that people still believe chemtrails are not real. it is right on from of your faces..wow!

  10. Steve Funk says:

    Some people don’t go along with begging the question and want credible evidence.

  11. JFDee says:

    Anonymous said:

    “it absolutely amazes me that people still believe chemtrails are not real. it is right on from of your faces.”

    Yes, we are all looking at the same same sky. The difference lies in the explanation of what we see.

    Chemtrail believers are often stating: “This <strange phenomenon in the sky> can’t be natural !!”. This in turn begs the question: “How do you know that ?”

    Can you name the specific facts that lead you to the conclusion that what you are seeing are chemtrails? Maybe you start with the most important one?

  12. Samples says:

    Does this site contain any sampling data from persistent contrails showing the chemical (or non-chemical) makeup?

    If so, excellent, could you please point me to it? If not, then wouldn’t the chemtrail theory be just as plausible as the persistent contrail theory?

  13. There are many sampling studies of contrails, example:

  14. Kodesh says:


    I want to see new data from the Chemtrailers. It is their job to prove the existence. This is not shifting the burden of proof, they assert there is a conspiracy theory a foot and it is their job to give evidence proving their theory. It is the role of the rest of the community to debate, discuss and together determine truth.

    As posted elsewhere. Chemtrails are entwined in the greater conspiracy theories of the NWO and global population reduction. Both of which have substantial evidence. Whether they are true or not is another story. The conflict of interest still remains… why would the ‘elite’ poison the same air they breathe?

  15. Bill says:

    There are a few problems with the persistent contrail theory and while I am an advocate of using science to confirm information I also recognize that science can be used in the other direction, as a justification for a particlar action. What has been ignored is that in conferences the “experts” have admitted to geoengineering for the purpose of adjusting weather patterns. Of course they are not going to produce volumes of papers because much of what they are doing is classified for national security reasons, however they do admit to “geoengineering”. If that is the case the question you must ask is what are they using to “engineer” because you can’t do that without a medium of some kind. You have also ignored the video footage that is available showing the trail immediately appearing at the wing of the plane. Contrails require the right RH and temperature combination. They do not appear immediately behind the engine but some distance away from the engine where the temperature and moisture combination hits dewpoint. At the engine the temperature is too high and so requires the distance to cool sufficiently. There is also the testimony of military personnel involved in the process and while that can be faked I do find it credible. We do know that the US military conducted chemical testing on the US population in various areas, one being St. Louis where housing projects were subjected to chemical disbursement for an extended period. No prior notification and no informed consent. In addition to all this you have not explained the criss cross pattern of trails. Flight “highways” follow a particular pattern and location since air traffic control would be much to difficult if you could not assign specific paths for flights under the existing system. Specific aircraft may be off by a mile or so in the path but they will not criss cross through the sky. Much too dangerous.

  16. cloudspotter says:

    Bill, everything you have mentioned has already been covered in depth on here and on Metabunk.org. Have a good look around.

  17. Strawman says:

    Empty claims. Evidence, please.

  18. captfitch says:

    Bill, since your last few statements are wrong regarding flight traffic I’ll have to assume everything else you know about aviation is wrong.

  19. Samples2 says:

    I would like to see the two replies from @Samples that the admin has decided not to post for some reason. I think they made legitimate scientific points.

  20. I don’t see any posts by “samples”

  21. Samples2 says:

    For some reason none of my replies are coming through.

  22. Samples says:


    Thanks for the link. That was an interesting study done on how jet exhaust can form into cirrus, how they interact with pre-existing cirrus, and the radiative properties taken on. No mention of a specific chemical makeup though, as I don’t think they were even studying that aspect. The fact that they flew through their own exhaust is rather questionable as well.

  23. Samples says:


    At any rate, I’m wondering if there is any more recent data. Most “chemtrail theorists” believe this activity ramped up in the late 1990s, at least from what I’ve gathered on the issue. I did find a study done in 1996 that does mention some chemical makeup, but even so, it was done on the coastal environment in the Los Angeles Basin, and not the actual exhaust trail:


    I did find this snippet of interest though:

    “The operation of jet engines results in the release of HC, CO,
    NOx, sulfur dioxide (SO2), and particulate matter. Assessments of
    the impacts of engine emissions and considerations of methods of
    reduction have focused more on the pollutants CO, HC, and NOx
    because much more information is available on them. The 1994
    EPA report Air Pollution Mitigation Measures for Airports and
    Associated Activity omits particulate matter from its discussion of
    airport emissions, stating, “little is known quantitatively about jet
    engine particulate emissions” (4).

    4. Energy and Environmental Analysis, Inc., and K.T. Analytics, Inc. Air
    Pollution Mitigation Measures for Airports and Associated Activity.
    California Air Resources Board, California Environmental Protection
    Agency, 1994.

  24. Samples says:


    I’m going to keep digging around to see what I can find. I’m inquiring on all of this because there does not appear to be definitive proof on what chemicals or particulates are, or are not, coming out in jet engine exhaust. From a scientific point of view, although this site has a wealth of knowledge and data on how jet exhaust appears and forms in the sky, it appears to lack any evidence on what that exhaust is actually made up of.

    I still say without that definitive proof, the chemtrail theory is plausible, and is most likely tied into geoengineering somehow. A search for the term ‘geoengineering’ on the USA.gov website yields 27,000+ results (wow). One of the first results I looked at is a power point presentation given in April 2008 about the possibility of using sulfate aerosols to combat “global warming”, essentially mimicking a volcanic eruption the size of Pinatubo. In it, one of the slides states that the US was spending $20 million/year on weather modification research by the 1970s. It also says that in 1945 John von Neumann organized a meeting at Princeton to discuss “deliberate modification of weather”. It also states that in 1955 he gave an interview with Fortune magazine speculating that:

    “Microscopic layers of colored matter spread on an icy surface, or in the atmosphere above one, could inhibit the reflection-radiation process, melt the ice, and change the local climate…”

    Neumann was one of the smartest men of the 20th century.

    I think we’d all be a little naive to not believe that our government is somehow involved in weather modification, whatever the scale. And we’re not talking about local cloud seeding with silver iodide. If we strip everything down to the basic scientific facts, what do we have?

    Missing data and inconclusive evidence.

    I look at it this way. There is no conclusive evidence for dark energy, but that isn’t stopping physicists from looking for proof that it exists. The same should hold true for any theory, regardless of how ridiculous it may seem at the surface.

  25. Samples says:

    Apologies for the multiple posts. Must not have liked the link to that PDF.

  26. cloudspotter says:

    “If we strip everything down to the basic scientific facts, what do we have?”

    We have white lines left by jets across the sky that look and behave exactly like contrails.

  27. Jay Reynolds says:

    samples wrote:
    “One of the first results I looked at is a power point presentation given in April 2008 about the possibility of using sulfate aerosols to combat “global warming”, essentially mimicking a volcanic eruption the size of Pinatubo.”

    Glad to see you used the word “possibility”. Also it is great that you can understand the analogy with volcanism which is how the idea of geoengineering came about. I’m going to show you something here that you won’t get at any chemtrails site.

    In 1998, Edward Teller proposed Stratospheric Radiation Management (SRM)” in his article “A Sunscreen For Planet Earth:

    He looked at the result of the Mt. Pinatubo eruption in 1992 and saw that it cooled the planet by ejecting 20 million tons of sulfur dioxide into the atmosphere, and proposed that humans could do the same to cool the planet.

    Chemtrail conspiracy theorists have been claiming that persistent contrails are evidence of SRM.

    If SRM were taking place, it would be evident in atmospheric readings of the transmission of solar radiation through the atmosphere, some of it would be blocked and transmission would decrease as it had during past eruptions.
    If SRM were taking place, transmission would decrease. Luckily, such data has been collected for fifty years and is available for examination on a daily basis. It is taken worldwide at ground stations and by satellite.

    Here is a graph of such transmission:

    Note the effect of Pinatubo, and also note that no such change has occurred. Indeed, the transmission levels are no different than ordinary background levels since 1955. This disproves, probably more than anything else, the claim that SRM has been taking place.


    Now, go to the people who have told you about geoengineering and ask them to address this issue.
    They will turn on you with threats of banning and accusations of dishonesty. They cannot face the facts, the truth is not in them.

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