Delta3 said, "
It is the speed of that air mass that counts."
That's only part of the story. If the pressure doesn't count, then that whole Mt Everest thing is nothing to brag about.
Nick, I agree that putting that hover bubble argument to rest is way overdue. I also agree that the truth is the way to go. I think it's important to remember that throughout even the most pure theory, assumptions have been made. While talking about reducing induced velocity is satisfactory to explain ground effect, that does not mean that pressure gradients can be ignored.
In the IGE case, the earth is effectively an infinite flat plate in the path of the induced velocity (downwash). The earth changes the direction of the down wash the same way air flows across/around flat plates. There will be a stagnation point. A static pressure difference can be measured. How big? This is where we realize why we bin the pressure argument from the start.
Matthew.
PS, will Gulfstream be in Paris? Time for a beer?