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