Re: HZ posters could figure this out. What resources and links can we access?
Sunblok! You posted a message! Cool!
LarryJ offered to map out flight corridors in a message downthread. That'll reveal a lot.
You yourself made a significant observation. Commercial air traffic was banned for several days after 9/11, and only carefully-monitored military and government craft were in the air. That strongly suggests that these contrails are routine civilian flights. That doesn't rule out some of them are military, of course. But all in all the contrails seem like an ordinary phenomenon.
--Robert