1. Trailspotter

    Trailspotter Senior Member

    This is a follow up to the thread https://www.metabunk.org/threads/squiggly-sinusoidal-thin-contrails-over-europe.3194/ that I think merits its own thread.

    In the above thread there are seven in total different occurrences of these highly unusual contrails captured on photo or video. I have trawled Google Images, flickr and youtube to find more reported occurrences and raised the total to more than 60 cases spanning over the past 15 years. One example has already made to the Wikipedia article on Contrail (English and Polish versions).

    Sinuous vapor trail over south-east Poland.

    Here is a selection of observed thin contrails (in three galleries):

    These numerous examples show that sinusoidal thin contrails are not a freak event but a recurrent albeit rare phenomenon. They are exactly what they look like - solitary hybrid contrails. Hybrid contrails are (parts of) exhaust contrails entrained in the wing tip vortices: http://contrailscience.com/hybrid-contrails-a-new-classification/. Normally, hybrid contrails come in pairs, like the vortices themselves. They are formed in a narrow range of RH and usually observed behind large planes that create stronger wake vortices, e.g., Boeing 747. The lifetime of a hybrid contrail pair is limited by the Crow instability (http://en.wikipedia.org/wiki/Crow_instability) that breaks down a pair of counter rotating vortices. Formation of solitary hybrid contrails apparently occurs in the same range of RH but additionally requires some form of atmospheric turbulence capable of decoupling the vortex pair. Solitary vortices can have a longer lifetime, therefore solitary hybrid contrails can persist, unlike a hybrid contrail pair.

    There are instabilities in solitary vortices causing vortex meandering, a phenomenon which has been observed in experimental studies of airfoil tip vortices in wind tunnels.
    Screen shot 2014-09-21 at 10.43.13.

    Solitary hybrid contrails display similar behaviour: in the beginning they form fairly straight lines and then transform into meandering shapes of gradually increasing amplitude. This phenomenon yet awaits its researcher, but the underlying causes are likely to be the same or similar to the causes of the Crow instability: an ambient turbulence and self induction of a vortex with itself. Playing on the name of its discoverer, I propose the name for the solitary vortex instability: the 'Rook' instability. Rook is a bird of the corvid family; the juvenile rook is similar to carrion crow, whereas their adults are readily distinguishable.

    Alternative explanation of the sinusoidal shape, as suggested in several discussions of individual occurrences of solitary thin contrails, is their perturbation by atmospheric waves. This explanation however can be ruled out by the observations of a sinusoidal thin contrail coexisting with an ordinary exhaust contrail from the same plane which is not perturbed (see the last gallery above).

    Below is a published account of one of the observation (from onlinelibrary.wiley.com/doi/10.1256/wea.266.05/pdf)

    More pictures of the above contrail are available at this link:

    Below are a few examples of 'newborn' solitary hybrid contrails:

    right behind the plane (like in the above description):

    at the end of a typical double stranded hybrid contrail:
    Full Size: https://www.metabunk.org/data/MetaMirrorCache/39a379cd272be87788ddb6b0248b297e._.jpg

    and (taken by some guy from Santa Monica);)

    detached from the rest of contrail:

    followed by evolution of the detached segment:

    Solitary hybrid contrails compared to ordinary hybrid and exhaust contrails of similar ages:
    Rook contrail gallery 4.

    Solitary hybrid contrails in 3D

    In at least two cases, the solitary hybrid contrails have been observed from different locations and photographed at about the same time. Using these photographs I have reconstructed the contrails' shapes in the form of pseudo stereo images:

    thin contrail 6 stereo.
    Rotterdam, February 18, 2013

    thin contrail 7(G).
    Göttingen, January 22, 2014

    Neither of these two contrails lays in one plane. Both consist of a number of irregular helical turns, the shapes of which resemble a stretched paperclip rather than a coil spring. Viewed at some angles, such irregular helical shapes may look very different from a sine curve, like, for example:


    Appeal to the readers:

    A solitary hybrid contrail is a very rare phenomenon. Therefore, if you happen to see one, please observe it thoroughly. Please note the time and place of observation and report it here asap. This would help the identification of atmospheric conditions as well as the types of planes and would facilitate further research of this phenomenon.
    Last edited by a moderator: Apr 25, 2017
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  2. Trailspotter

    Trailspotter Senior Member

    Appendix 1.
    Distribution of known occurrences of solitary hybrid contrails by country.

    occurrences from the previous thread https://www.metabunk.org/threads/squiggly-sinusoidal-thin-contrails-over-europe.3194/

    EDIT: I did not intend to embed the youtube links, it happened automatically.

    UK (10):

    *London Heathrow, September 1, 2001

    *Berkshire (Reading and London Heathrow), November 19, 2005

    Wales, February 6, 2008

    Scotland, February 13, 2008

    Kent, March 7, 2008

    Norfolk, March 19, 2011

    Oxford, November 30, 2011

    Cheshire, November 6, 2012

    Wiltshire, February 19, 2013

    Cornwall, May 15, 2014

    Netherlands (8)

    December 18, 2006

    February 9, 2008

    October 9, 2009

    March 22, 2011

    https://www.flickr.com/photos/redratz/8487855262/ (34 MP)
    *February 18, 2013

    *March 4, 2013

    April 15, 2013

    https://www.metabunk.org/threads/squiggly-sinusoidal-thin-contrails-over-europe.3194/ #1
    *January 12, 2014

    Germany (8)

    Berlin, March 24, 2006

    Göttingen, October 2006

    Braunschweig, Germany, January 5, 2008 (?)

    February 11, 2011

    Bavaria, October 5, 2011

    Göttingen, January 12, 2014

    Göttingen, January 22, 2014

    Place and time unknown

    USA (6)

    California, May 12, 2000

    Iowa, December 7, 2002

    *Kansas, December 17, 2007

    Pennsylvania, March 3, 2011

    Montana, January 5, 2013

    Utah, April 14, 2013

    Poland (4)

    *April 21, 2009

    August 19, 2009

    March 2, 2011

    March 21, 2014

    Czech Republic (4)

    December 14, 2006

    November 21(?), 2011

    February 16, 2012

    April 14, 2012

    Belgium (3)

    May 24, 2011

    May 31, 2014 (observation of two thin trails with a 30 min interval)

    Sweden (3)

    Lund, February 11, 2010

    Stockholm, April 25, 2011

    Place and date unknown

    France (2)

    Rhone-Alpes, March 1, 2011

    Toulouse Blagnac Airport, February 29, 2012

    Russia (2)

    Tatarstan, May 15, 2005

    St Petersburg, October 6, 2010

    Denmark (1)

    October 23, 2011

    Finland (1)

    September 5, 2011

    Bulgaria (1)

    https://www.metabunk.org/threads/squiggly-sinusoidal-thin-contrails-over-europe.3194/ #27
    *March 18, 2010

    Romania (1)

    June 6, 2009

    Hungary (1)

    November 20, 2012

    Canada (1)

    Ottawa, March 24, 2009

    Japan (1)

    January 28, 2013

    Australia (1)

    Victoria, August 20, 2011

    Unlocated (3)

    European airspace, March 28, 2009

    in the air, April 21 2009

    unknown location, at least two years ago

    The leading position of UK is likely due to a bias of my searches toward English compared to other languages that I've searched with. However, the European dominance over the rest of the world is significant. The reasons for this is yet unknown. It could be due to an increased occurrence of clear air turbulence that correlates with the position of jet stream and/or a higher density of large aircraft routes over central Europe.
    Last edited: Sep 21, 2014
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  3. Mick West

    Mick West Administrator Staff Member

    Excellent work!

    This seems like a very good explanation for all the observed squiggly contrails. Particularly compelling is this image:

    Which shows a trail almost exactly like those observed, and the entire evolution from plane to squiggle.

    Not quite as good is the photo I took on dec 21, Santa Monica, looking west from Santa Monica. I dug up the original for a higher resolution image taken 4:13:22 (camera time)

    and the two planes in a wider context at 4:12:31, 51 seconds earlier
  4. Mick West

    Mick West Administrator Staff Member

    Last edited: Sep 21, 2014
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  5. deirdre

    deirdre Moderator Staff Member

    so did the vortices do this to the clouds? or is that something else?
  6. WeedWhacker

    WeedWhacker Senior Member

    I think it's a combination of factors....but you're on the right track.....

    The "sinusoidal" element that causes "some" persistent contrails to develop in that visible way is likely due to atmospheric processes....partly as a result of the way the airplane can affect the air "currents" as it passes (**)....and also how the existing atmospheric forces, PRIOR to when the airplane entered, are going to interact.

    (**) The wingtip vortices, that are produced....for example....

    The airplane can be a "trigger" in this interpretation. Of course, "Mother Nature" uses other "triggers", long before airplanes were invented by Humans.

    Also....since clear air is (virtually) transparent to Human eyes. When clouds form it tends to "draw attention". But the currents....whether horizontal, vertical or a combination? Of "clear" air are invisible...we only see the effects of such currents ON the clouds, which are "visible"...this includes contrails, of course.
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  7. skephu

    skephu Senior Member

    So is it in reality more helical rather than sinusoidal? Sinusoidal imples that the contrail lies in a plane.
  8. Mick West

    Mick West Administrator Staff Member

    A helix is sinusoidal, just in three dimensions. The point is more that it's a 3D squiggle, not a 2D squiggle.
  9. skephu

    skephu Senior Member

    A helix is not sinusoidal. The projection of a helix may be sinusoidal. The word sinusoidal imples a 2D curve lying in a plane.
    The point of my question was whether this contrail lies in a plane or is a 3D helix.
  10. Trailspotter

    Trailspotter Senior Member

    In reality, or more accurately, in my 3D reconstructions, the helical turns are rather flat. A good approximation of the contrail shape is a wire loosely wrapped around school ruler: P1210506.JPG

    viewed from a flat side it is sinusoidal.
  11. Mick West

    Mick West Administrator Staff Member

    Getting into semantics here.
    So a helix is definitely sinusoidal by the dictionary. People's personal usage of the word might vary.

    But I think I answered your questions with:
    However looking at all the examples above, they seem (as Trailspotter noted) rather flat. Just not always entirely flat - and this variation can give some trails that look odd from some angles, especially this example:

    With that one you have to think how it could be laid out on a flat surface with none of the "loops" actually crossing. Then perspective and some vertical displacement gives the illusion of loops.
  12. skephu

    skephu Senior Member

    What makes it flat?
    I also wonder what determines the direction of the flat side. Is it usually vertical, horizontal, or random direction?

    BTW does anyone know a meaningful explanation of the Crow instability? The Wikipedia description is obscure to me.
  13. Mick West

    Mick West Administrator Staff Member

    The simplest explanation is that two parallel vortices that rotate in opposite directions in a fluid are inherently unstable, and will interact with each other - magnifying existing irregularities in each other.

    All planes have these two wake vortices, regardless of if you can see them. So they all have these squiggles in the air behind them. You just only see them when a hybrid contrail forms in them.
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  14. Trailspotter

    Trailspotter Senior Member

    This is a good question, to which I know no answer. Finding it would require more observational data and a professional research. You can get some idea about these from the Crow's original article (a free copy of which is available at http://flair.monash.edu.au/seminars/2007/Crow_1970.pdf).
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  15. FrankN

    FrankN New Member

    Above The Hague (Netherlands) (very near the royal stables) looking due west on 18-02-2015 around 16:00
    There was a contrail like the ones in this forum. Very sharp, and curvy. It reminded me of a rocked fail.
    I did not take a picture and the trail disappeared quickly in about 10 minutes after I had first seen it the trail was almost gone. Looking at google maps I figure this contrail must have been above sea near Hoek van Holland
    Hope this helps.
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  16. Mick West

    Mick West Administrator Staff Member

    Also spotted by Willem, who emailed me this, with pics
    CET is UTC+1, so 16:00 CET is 15:00 UTC
    Location is 52.0094494,4.3354893

    photo (13).JPG photo (16).JPG photo (15).JPG photo (12).JPG photo (14).JPG
    Last edited: Feb 19, 2015
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  17. Trailspotter

    Trailspotter Senior Member

    Thanks to @FrankN and Wilem for this observation. I will look into it this weekend, after I return home from traveling. I've checked FR24, there were a few planes above the area at the time. My favourite candidate is SIA308 Airbus A380 that flew over it ten minutes earlier, at about 14:50 UTC.
    Last edited: Feb 19, 2015
  18. Mick West

    Mick West Administrator Staff Member

    That certainly matches Willem's viewpoint in the park (note I copied the wrong coordinates, which should have been 52.0094494,4.3354893, just a few hundred feet away though), and is looking towards the Hook of Holland, as @FrankN reported.

    Attached Files:

  19. Mick West

    Mick West Administrator Staff Member

    Of possible interest, the plane had just started to descend at that point and going from 40,000 ft through 30,000 feet as it approached the horizon

    The trail in the photos though would likely only be a portion of this, as it seems to be nearly overhead down to the tops of the trees, still at a fairly high angle.
  20. Trailspotter

    Trailspotter Senior Member

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  21. Mick West

    Mick West Administrator Staff Member

    Another photo has emerged from the same day, but nearly two hours later.

    Ghent-squiggly contrail-IMG_20150218_174800.
    Photo: Tim BAETENS, (c) CAELESTIA/Belgisch UFO-meldpunt


    In this case, the location and direction can be more accurately determined, as around 51° 2'28.14"N, 3°43'36.20"E, about at the intersection of Kantienberg and Kramersplein, taken from inside a car.

    A likely candidate is RBA98, a 787 from London to Dubai (kml attached)

    In this case it was climbing out of London, not descending towards it, but would still have been at around 34,000 feet over the coast, and then 35000 when overhead. The apparent angle above the building puts it between the coast and Bruges. So would have been quite visible in this region:

    The drift of the trail from the radar track matches the wind direction from the earth.nullschool.net images above.

    Attached Files:

    Last edited: Apr 3, 2015
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  22. Trailspotter

    Trailspotter Senior Member

    I found a series of photos by A380spotter depicting an interesting case of contrail evolution. Two Cargolux B747s, LX-VCA and LX-SCV, crossed their paths over Heathrow on April 6, 2015 at about 16:00 BST (15:00 UTC):

    Each plane left a pair of hybrid contrails:

    However, the evolutions of these pairs were different. In one pair the trails dissipated simultaneously through the Crow instability, whereas in the other pair one of the trails dissipated quicker than the other:

    Unfortunately, there are no further pictures featuring evolution of the remaining solitary thin trail, that I believe would have got squiggly. Also, unfortunately, I found this series too late to check on FR24 which plane was which and what were their courses, altitudes, etc.
    Last edited: Apr 26, 2015
  23. Trailspotter

    Trailspotter Senior Member

    I have found these flights on Planefinder.net. I have never used this server before, and I will have to explore it more, as it allows playback of earlier flights than provided by free version of FR24.
    Cargolux cross.
    The solitary hybrid contrail came from CV436 (CLX436) LX-VCA. Interestingly, this plane was higher at 39,000 ft, but appeared to produce a wider gap between its initially two hybrid contrails, than LX-SCV at 37,000 ft.
  24. Ian Jacobs

    Ian Jacobs New Member

    Very well done! I especially like the first stereo pair. To my eye that shows the trail confined to a plane as a first approximation. If we define the principle displacements to an x,y plane then displacements in the orthogonal z direction amount to 10 % or less if the x,y displacements. I think it may be misleading to describe the path as a helix. Displacements in the z direction seem to me to be a small and possibly somewhat irregular secondary effect.

    Thank you for the explanation, which makes complete sense to me. (I had wondered if the thin trails were perhaps the result of wingtip trails only of which I have one example, but your explanation discounts that. I also agree that KH instability in the atmosphere cannot be the mechanism. I have one example of a trail that I think is disturbed by a kH instability and it looks nothing like the tails above.) Those images are not relevant here, but if you would like to examine them for interest I can put them somewhere.

    Best regards

  25. Trailspotter

    Trailspotter Senior Member

  26. Ian Jacobs

    Ian Jacobs New Member

  27. Mick West

    Mick West Administrator Staff Member

    And if there's photos you have questions about, you can start a thread sin the Skydentify forum:
  28. Trailspotter

    Trailspotter Senior Member

    New photos of solitary hybrid contrails from Germany. The top one appears to be very recent (the last week?)

    Dieses Foto unseres Users Ferdinand Kröger, aufgenommen am Donnerstagnachmittag südlich von Reit im Winkl, sorgte für einiges Rätselraten bei Experten und unseren Usern.
    © Ferdinand Kröger

    Eine Userin hat diese Linien im März in Nordhessen fotografiert.
    © Cordula Bernert

    Last edited: Nov 24, 2015
  29. A380

    A380 Member

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  30. Trailspotter

    Trailspotter Senior Member

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  31. Trailspotter

    Trailspotter Senior Member

    From https://diary4dan.wordpress.com/2015/12/15/crazy-contrail-contortions/
    This seems to be a busy path in both directions. By the time it could be one of the three A380 that went along it in easterly direction shortly before 15:00 UTC (16:00 CET). The latest one was UAE16:
    Screen Shot 2015-12-15 at 20.15.30.

    The camera actually was facing South West, there the Sun was at the time. Its position can be derived from the convergence point of the shadow lines.
    Last edited: Dec 15, 2015
  32. Trailblazer

    Trailblazer Moderator Staff Member

    Could the fact that it is a busy path be significant? A380s are big aircraft and must produce a lot of vortex turbulence. Perhaps the timing just happened to be right for the contrail from one aircraft to get caught up in the turbulence from a preceding one?
  33. Trailspotter

    Trailspotter Senior Member

    I have copied here a part of my recent post in related thread:

    I have found an approximate viewpoint of the above video. Like another recent video by the same author, it probably was "timelapsed with GoPro Hero3 Black", FOV of which is wider than the ground level view in Google Earth. The QTR40 track downloaded from FlightAware and the Sun position at 15:14 UTC give a nearly perfect match to ground landmarks and other features:
    Screen Shot 2015-12-29 at 18.46.33.
    QTR40 GE.

    Thus this trail indeed was left by a A380 plane flying a level flight at 39,000 ft. The earth.nullschool.net forecast at 250 hPa suggests there was a 30 km/h tailwind at a slightly lower altitude, but the wind direction was changing from westerly to northerly in this general area.

    Using FR24 and FlightAware, I have identified flights for other contrails in the time lapse video, OK725 at 00:00 (corresponds to 14:48 UTC) and AZ404 at 00:17 (15:22 UTC). Thus the time acceleration factor is about 2 minutes of real time per second of the video and the lifetime of the solitary hybrid contrail was about six minutes.

    Attached is a KMZ file with the QTR40 track, the camera viewpoint and the location of a local landmark La Vedetta at the top of the mountain on the left.

    Attached Files:

    Last edited: Dec 30, 2015
  34. Trailspotter

    Trailspotter Senior Member

    Today, March 25, 2016, I have observed the formation of a solitary hybrid contrail, but, regrettably, it's dissipated without developing a clear sinusoidal shape.

    A Cargolux Boeing 747 passed southwest of my location around 12:50 UTC:
    Screen Shot 2016-03-25 at 12.56.14.

    Initially, it left a typical hybrid contrail, in one segment of which the contrail strands were separated notably wider than usual:
    One of the strands in this segment dissipated rather quickly, whilst the other strand remained for longer and developed a wavy shape before dissipating itself. However, the wave amplitude (in the direction perpendicular to the line of view) was rather weak:

    The elapsed time from the formation of this contrail segment to the dissipation of its last strand was about 5 minutes. The last solitary strand outlived a later (younger) segment of the same hybrid contrail, which dissipated in a 'normal' way (through the Crow instability):
    Last edited: Mar 25, 2016
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  35. Trailspotter

    Trailspotter Senior Member

    In flickr, there are recent photos of a new occurrence of a sinusoidal thin trail on March 24, 2016:
    [​IMG]Solitary hybrid contrails; the 'Rook' instability by Mila Zinkova, on Flickr

    The photographer Mila Zinkova lives in San Francisco. Her name has already been mentioned here in another thread on unusual multiple halos over SF:

    We have quite a few members from the SF area. I wonder if any of them seen or heard about more observations of this trail?
  36. Trailspotter

    Trailspotter Senior Member

    Update on the previous post.

    The photographer confirmed the location and time of the photo and added that the camera was facing west, or north west. This gives the most likely culprit being the Korean Air Airbus A-380-800 KAL11 from Seoul to Los Angeles that passed over San Fransisco from northwest at about 20:55 UTC (13:55 PDT):
    Screen Shot 2016-04-10 at 09.05.13.

    The plane heading almost perfectly was aligned with the wind direction at 250 hPa, but the wind speed was gradually decreasing along the flight track.
    Unfortunately, despite it occurred over a big city (San Francisco), I was not able to find more records of the observation of this sinusoidal thin trail, with the exception of the Patrick Roddie's time lapse video:
    Screen Shot 2016-04-10 at 21.59.06.
    As his camera's exact location is known, the sun position in the sky can be used to determine the moment (1:15) corresponding the time of the solitary trail observation (21:00 UTC = 14:00 PDT). The Roddie's camera pointing to the South, i.e., in a perpendicular direction, captured a different segment of the KAL11 trail, that might or might not have evolved a sinusoidal shape. At the highest resolution (1440p60 HD) on a big screen, the western end of the trail does look squiggly, but a wide camera angle does not allow to see fine details.
  37. TEEJ

    TEEJ Senior Member

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  38. Trailspotter

    Trailspotter Senior Member

    According to the comment, the author of this collage has also observed and photographed the trail. I agree with this identification, as the positions of the sun and two nascent trail are consistent with the time on FR24 screenshot, but I'd prefer the time of observation being confirmed independently. Regrettably, the photos in the link are stripped off metadata.
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  39. Trailspotter

    Trailspotter Senior Member

    A new sighting of this rare contrail from Oxfordshire, UK on November 2, 2016 at about 08:42 UTC. Below is a cropped photo, full version of which can be seen on flickr: https://flic.kr/p/NMeANp
    Screen Shot 2016-11-10 at 14.01.12.
    The time and location have been verified by the photo's author.

    Once again, the most likely culprit was Airbus A380 (UEA206 A6-EDB) that passed over at FL370 about six minutes earlier.
    Screen Shot 2016-11-10 at 14.09.01.
    The ordinary contrail the most likely belongs to EasyJet A319 that passed over at the time of the photo along the same track at FL320.
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  40. Mick West

    Mick West Administrator Staff Member

    This is a good closeup:

    In particular it shows these "bumps" in the trail that are typical in a hybrid contrail where you can actually see them spinning.

    Here's a closeup of a more typical hybrid contrail pair that shows the spinning:

    Source: https://www.youtube.com/watch?v=nfwejwWlmt4
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