I've never noticed this before, so I'm asking. Shortly after SRB ejection, the RD-180 plume appears to be very asymmetric. Why is this? If I recall correctly, these are full-flow & there isn't any gas generator exhaust, so I was confused.
Is this "bulge" in the plane between the two nozzles & thus representing a higher-pressure region between the two plumes? Is there some other reason?