There is something called the boundary layer, which varies in thickness depending on the flow at that point. The air at the boundary layer moves a lot slower (i.e. surface friction with the car body slows it down) than the air further out. I think it is along the lines of the first layer of molecules next to the skin are static and each layer of molecules working out gets closer to the air speed of the free air. Maybe that's what you see with the smoke trails? As far as I know the detail of what the boundary layer does is very important.
Think about how much attention people spend making the surfaces as smooth as possible. The skin has to be smooth and any joints between body panels tend to be taped up.
I know someone who makes grahics for some F1 (and other race) cars - he says that they are very fussy about sticker thickness and spend large amounts of money on the thinnest stickers possible.
When the air runs over the body it creates friction drag.
What you are seeing is what happens to the smoke trail/air at the level the smoke enters the air stream. If it was held lower it would get closer to the body work and touch it to. Dont forget that all the air from just below the bonnet line is forced up and over the windscreen and roof, hence the movement of the smoke trail.
I don't understand why F1 teams dont apply decals etc. to the body panels then varnish them again to provide a smooth finish for maximum effect? They always seem to apply the decals last...
Have you ever tried wrapping a rugby ball so that the paper, fits snuggly to the surface and is neat and tidy with no overlaps Thats why the whole car isn't decalled
Thats why the whole car isn't decalled