Konstantinos Kourtidis 9 years, 7 months ago

The ring is a result of the so-called Crow Instability. In aerodynamics, the Crow Instability is a line-vortex instability, named after S. C. Crow. It 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 instability goes through several stages, at one fo which waves reconnect, forming the contrail rings as the one photographed here.