I think it's ground (based (based on a Flash Gordon episode) )
The prop wash from the plane with the red fuselage on the right is retro-reflected forward in a counter-clockwise spiral because the rotation of the earth is slowing by a second per year. The reason the plane to its immediate S.E. is spared from the harmful retro-reflective energy of the prop wash is only because the boomerang shape of the jetway between them cancels the harmonicas of the perturbation.

Yet another reason we all need to walk counter clockwise