I hadn't noticed it before, but after seeing yesterday's recap video of the recent Launch and Landing of the Falcon 9, I'm wondering what the plume visible during ascent is.
You can see it clearly immediately after launch, when the video changes camera angles at around 1:04, but I've highlighted it below:
I assume it's the fuel gases continuing to be vented, and the plume appears to extend/originate from up the stack.
However, is the lower, circled part, just being illuminated by the light from the engines, or is it actually being ignited? Does the plume have any measurable affect on the attitude that the rocket has to correct for, either through the venting or ignition (if indeed it is alight)?