Crow Instability

Watching airplane contrails overhead, you may have noticed them transform into a daisy chain of distorted rings. This is an effect known as the Crow instability. The contrails themselves are the airplane’s wingtip vortices, made visible by water vapor condensed out of the engine exhaust. These two initially parallel vortex lines spin in opposite directions. A slight crosswind can disturb the initially straight lines, causing them to become wavy. This waviness increases over time until the vortex lines almost touch. Then the vortices pinch off and reconnect into a line of vortex rings that slowly dissipate. Be sure to check out the full-resolution version of this animation for maximum effect. (Image credit: J. Hertzberg, source)

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