What supersonic aerodynamics phenomenon is seen here?
 

I'm curious what supersonic aerodynamics phenomenon is seen on this interesting rocket photo? The linked page describes the event, but I'd like to add that this photo is a high-quality colour version of the frame at 0:09:02 (min:sec:frame) of that 1.5 MB greyscale video clip. The exhaust gases seen are from the recent firing of the 8 relatively small solid fuel rockets located at the "tail" of the rocket's first stage whose thrust is directed opposite of the thrust of the propulsion engines in order to quickly jettison the stage.