So, can we agree to the definition of downflow as a flow
of air toward the ground and define the induced downwash
as the velocity of that air near the wing?

I don't think this is a useful definition. Downflow and downwash are
the actual movement of something, not merely the velocity of that movement.

Plainly if air flows to the Earth and *stops* there as
you wrote, it has displaced other air which flowed
up to replace it, right?

Only if pressure is constant. (at constant temperature). However,
pressure does not remain constant. The pressure below the wing (and
thus against the earth) increases due to the extra molecules that have
been thrown down. Those molecules came from above the wing. The upper
atmosphere =is= (slightly) depleted by the flight.

Jose
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