Here in southern Connecticut we get a lot of chemtrail X's and zig-zags in the sky also. They linger and expand into huge formations or sometimes just dissipate.
I watched through binoculars once as a jet turned-off it's "smoke" trail and cruised for a few seconds with no exhaust visible at all... then the "exhaust" sputtered on again and continue to flow out heavily until the jet was out of my view.
Good that you are conscious of it and pushing for answers.
I have noticed the same thing as you. Was told by doubters this effect is caused by different temperatures in the air, though I remain unconvinced by this explanation.
yes.. the different air temps would be more layered/stratified. I saw the exhaust plume in my example that i described clearly sputter.. like someone was reopening a valve to release whatever they're using.