Looks to be a shock made visible by the relative position of the sun and aided by refraction of the black background colouring. Have look at
this link which talks about Schlieren photography .. the normal technique used to visualise shocks.
Characteristic normal shock where locally supersonic flow reverts abruptly to subsonic. The dancing about is quite characteristic of the unsteady flow nature of the shocks in transonic flow regimes.
Appears the boys may have been trying to make up a little on the schedule ? .. we've all been there, done that ...