January 19, 2004: The Crow Instability

In the series of interesting aircraft contrails spotted, here's one that particularly caught my interested in the weekend.

Sighted Sunday from the Windsor Great Park near Heathrow (where, inevitably, there is a high frequence of flyovers by various sized aircraft), this contrail was shaped like "smoke rings" from a giant cigar. I whipped out the camera and took a few shots. A close-up of the phenomenon is seen here:

Aircraft contrail ''smoke ring'' presumably caused by the Crow Instability

Some searching online tells us that this is caused by the so-called Crow Instability in the vortexes caused by aircraft; whilrling the otherwise straight contrails into spirals then donut-shaped rings. More about this in Scientific American:

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.

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.


I thought a topic like this would definitely inspire many bloggers. At least more than nothing. Bad luck there is noone here

Posted by: Christian at February 3, 2004 04:26 AM

Thanks for the explanation - I didn't know anything about the Crow Instability.
May I ask a question: do you always have your camera with you? The pics are great! When I see something great, my camera is always at home...

Posted by: Ambulance Girl at November 27, 2004 01:27 AM

Cool stuff. There are a lot of tin foil hat people that think that those donut rings are caused by some experimental flying contraption possibly using alien technology =)

Posted by: Deraj at February 2, 2005 07:00 PM
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Additional stock photography keys: Cloudscapes, London, plane, travel, aircraft, vortex, vortices, vortexes, vortice, cigar, ring, donut, donuts, white, blue, horizontal, sky, cloud

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