Those were made by small rockets fired off instants before the bomb went off to generate smoke trails so as to give a visual indication of the propagation of the shock wave.
Actually, i read somewhere it was otherwise, they were created by some static electric discharge or something created by the blast initial effect, not effected by the shock wave or to measure the shockwave
“Actually, i read somewhere it was otherwise, they were created by some static electric discharge...”
I never read that, but I can’t claim direct knowledge. Any kind of static electricity discharge or orderly fields set up by the blast I would imagine would be obliterated by the sheer flood of ions and particles of all sorts emitting from the blast. That’s why I think (and have read) that they are just dumb smoke trails from rockets launched immediately pre-detonation. And, as you say, they are only visible on *some* of those early Nevada (NM, in the case of Trinity) blasts, which were all photographed in roughly the same fashion.