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Crow Instability

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martinastro
Martin Mc Kenna
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« on: January 18, 2011, 10:37:56 pm »

Ever herd of Crow Instability?, that's the name given to the strange forms seen in airplane contrails, I have always wanted to catch these on camera ever since Mike Hollingshead informed me about them and today I succeeded when a very high altitude jet flew over from SE to NW on Jan 18th approx one hour before sunset. I used the canon 100-400mm lens at 400mm for these which was sore on the arms. These forms are caused by vortices created by the wing tips of the plane which in turn effect the contrail causing vorticies to form there too. I saw loops, doughnuts, figures of eight etc..all these forms were rotating in a horizontal manner like fine white coloured rope tornadoes which was quite spectacular to watch through the 400mm lens. More info fronm wikipedia below the images.











In aerodynamics, the Crow Instability is an inviscid line-vortex instability, named after its discoverer S. C. Crow. The Crow instability is most commonly observed in the skies behind large aircraft, when the wingtip vortices interact with contrails from the engines, producing visible distortions in the shape of the contrail.

The Crow Instability is a vortex pair instability, and typically goes through several stages:

1) A pair of counter rotating vortices act upon each other to amplify small sinusoidal distortions in their vortex shapes (Normally created by some initial disturbance in the system).

2) The waves develop into either symmetric or anti-symmetric modes, depending on the nature of the initial disturbance.

3) These distortions grow, both through interaction from one vortex or another, and also 'Self Induction' of a vortex with itself. This leads to an exponential growth in the vortex wave amplitude.

4) The vortex amplitudes reach a critical value and reconnect, forming a chain of vortex rings
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rjgjr
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« Reply #1 on: January 19, 2011, 06:31:32 am »

Very interesting stuff Martin, I've heard a little about this phenomena before but never really have seen any photos. While still working in Irvine, in Southern California for the Street Maintenance Department, part of our street jurisdiction was in an Industrial Complex beneath the landing pattern for John Wayne International Airport. The jets would be just several hundred feet above some of the streets as they landed and you could here some of the strangest sounds of rushing, twirling and spinning air about 30 seconds after the jets went by. I would imagine  that was something similar but with audio instead. Thanks for posting.
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markt
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« Reply #2 on: January 19, 2011, 07:33:09 am »

Excellent stuff Martin!  Great pictures and an informative read!  Wink
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martinastro
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« Reply #3 on: January 20, 2011, 05:50:56 pm »

Thanks guys and thanks for the info Richard, that must be some experience hearing and feeling those jets landing at close range like that. I read that Crow Instability can be dangerous to other planes flying in it's wake. I got more images from the following day (19th) with the 400mm and cropped showing tubes, vortices, and dozens of ringlets/donuts which were amazing to watch...







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JohnC
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« Reply #4 on: January 20, 2011, 09:43:04 pm »

They're very interesting, I saw  a contrail that was like twining the other day but I didn't have time to catch it,I'll keep an eye on them in future. That 100-400 is opening up your world,Martin. See if you can get in on a bird or two at Lough Neagh.
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