I caught this Crowe instability in a contrail Saturday, October 22, 2016 at 5:24 pm looking northwest over the Flatirons in Boulder CO. I have loved watching the self-induction of elliptic vortex rings ever since I studied them as a post-doc at USC in the late 1980’s.

Handheld my Canon T3i. It was pretty easy to stabilize and assemble the gif in Photoshop.