I'm no weather expert, but am pretty sure there's no way a rainbow appears as a circle, regardless of where you are. They always have to touch the ground don't they, cus of the way they work? They're made by light passing through air with moisture in it, at an angle. When you say they appear as a circle, do you mean just sort of a floating disk of colour? Regarding seeing rainbows from above, I've seen rainbows from above from a plane window. In this case it still appears as an arch in the sky still reaching to the ground.