After the airplane lands how does the air return to ambient
pressure, at a higher temperature, (or at any rate at a not
lower temperature) without any upward flow?

After the airplane lands, the downflow from the wings ends. The
downflow from the wings is what keeps the air above rarified, and the
air below squished. Once that is removed, the pressure below can
relieve itself by having the air flow upwards a sufficient amount.

AT THAT POINT, the air has returned to its normal pressure distribution,
(albeit slightly warmer). But so long as the airplane is flying, it has
to be supported by the air, and the pressure below the wing is greater
than (and the pressure above the wing is less than) it would have been
absent the continuous downflow induced by the wing in flight.

Similarly, for a fan in a closed room, the air pressure on one side of
the room will remain higher than the pressure on the other side, until
the fan is turned off. Then the air will spring back.

And similarly, when you sit on a chair, it deforms slightly. When you
get up, it springs back (unless you broke it!)

Jose
--
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