The amount of air pumped down for a Boeing 747 to create lift for its roughly 800,000 pound takeoff weight is incredible indeed. Pumping, or diverting, so much air down is a strong argument against lift being just a surface effect as implied by the popular explanation. Figure 6 illustrates the effect of the air being diverted down from a wing. A huge hole is punched through the fog by the downwash from the airplane that has just flown over it. When the air is bent around the top of the wing, it pulls on the air above it accelerating that air down, otherwise there would be voids in the air left above the wing.
Air is pulled from above to prevent voids.
This pulling causes the pressure to become lower above the wing. It is the acceleration of the air above the wing in the downward direction that gives lift.