F1 Rear Wing Vortices
For narrow aspect ratio f1 rear wings this it comes largely from induced drag created by wing tip vortices which are spiralling airflows created where the high pressure above the wing tip roll over into the lower pressure areas beside and below the wing tip.
F1 rear wing vortices. The air moves at a higher velocity beneath the surface of the rear wing and at a lesser. As the spoon wing reduces the geometric angle of attack towards the tips it changes the spanwise wing tip to wing tip. The rear wing vortex pair is also a large constituent of the aerodynamic wake which is ultimately also detrimental to a following car. Close up of a spoon rear wing.
Interestingly creating more downforce from the rear wing with a smaller aspect ratio thereby increasing the tip vorticity and induced drag can be beneficial to a following car but thats for another article. These thin white streams are nothing but vortices of air produced when the rear wing generates downforce. These are the vapour trails seen on damps days curling from the wing tips.