Wikipedia describes ground effect as "the increased lift (force) and decreased aerodynamic drag that an aircraft's wings generate when they are close to a fixed surface."
That's all fair and good, but when they state "close to a fixed surface" they pretty much assume the surface would be the ground or another large surface under the wing (hence the name).
What I'm wondering is, in the unlikely event that a plane were to fly near a ceiling (so the fixed surface would be over the plane), what would be the net effect? Will there be more, or less lift? Drag? Is there something else that could be affected which I'm not considering?
I can't think of any realistic scenarios where this could happen besides someone flying an RC toy plane in a warehouse (that's probably why it's much less documented than ground effect) but I was thinking about this and was curious.