# Does anyone know the mechanism behind this double helix cloud formation?

This looks like m=2 swirling instability mode of the axisymmetric jet, but how could an axisymmetric jet form up in the sky like that?

• Could you be looking at the core of the jet stream? Where was this picture taken? Nov 8 '14 at 4:15
• @Floris, No idea where it was taken. I guess it could be the core of a jet stream, but aren't those supposed to be over a mile thick en.wikipedia.org/wiki/Jet_stream. Nov 8 '14 at 4:53
• It is difficult to judge the height at which this phenomenon occured. From the article mdornfe1 mentioned, I would guess that some obstacle in the air can trigger this slowly swirling motion. I must admit that I didn't read the article carefully enough, but the Reynolds numbers and stability mentioned there indicate that a scaling from wing tip swirls to some 100 m could really work. Maybe big platforms of television towers (imagine the bis ball of the berlin tower) can induce this double helix in just the right amount of wind speed and atmospheric stability. Dec 2 '14 at 9:45

• Your over their length link is broken. May 29 '17 at 13:30