On one level you can say it's a consequence of the bound vortex around
the wing. Not satisfying? I agree, but that's about as far as most
aerodynamics books go in providing an intuitive answer.

Ok, how about looking at it this way:

Consider the earth and an atmosphere consisting of one air molecule.
(Let's not get into the fact that there's really no such thing as an
"air" molecule, and yet leave the actual choice of gas... uh... in the air)

The molecule starts out motionless (say) a hundred miles above the
earth. Gravity pulls the two of them together, they accelerate towards
each other until the molecule bounces (perfectly) on the surface of the
earth, whereupon both the earth and the molecule return to their
original position and resume the dance. This is air pressure at its
simplest. Momentum is conserved; the total momentum (earth and air
molecule) is always a zero vector sum. The momentum of the air
increases as it accelerates downward, and when it bounces it transfers
its momentum to the earth. The earth does likewise. No net movement of
air.

If a wing is suspended some distance above the earth, it will also begin
to freefall and acquires momentum downwards (the earth is pulled towards
the wing too and acquires an equal but opposite momentum upwards). In
order to remain aloft, the wing grabs an air molecule and flings it
downwards with great gusto, that is, with a momentum equal to what the
wing had acquired. This is sufficient to cancel out its downward
velocity. This air molecule now has an excess momentum which it
transfers to the earth upon impact, cancelling the earth's motion
towards the wing. Net momentum is zero, but as it bounces back up, it
pushes the earth back down where it belongs. Earth has acquired a
downward momentum, the molecule now has an upwards momentum. The
molecule bounces back towards the wing, transfers its excess upwards
momentum to the wing, and pushes the wing back up where it belongs.

At this point the earth is moving down and the wing is moving up.
Gravity slows them down to zero just as they reach their original point.

No net movement of air.

Air pressure works this way to keep the earth away from the wing.
Overall, there is no net movement of air. However, as far as the wing
is concerned, it is flinging air molecules downwards, where there is no
room for it. This increases pressure underneath the wing, and that
pressure manifests itself in upwards motion of the air which helps to
support the wing.

The higher pressure area is in front of the wing because the wing has to
push air away from it in order to pass through it.

Jose
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