Alan Baker wrote:

Pressure waves can reach the ground, without the air in the column
descending to the ground.
I never said that the particular molecules that the aircraft touches
are the ones that have to reach the ground.
You said "The net flow is downward until it hits the ground and the
momentum is transfer to the earth."

And it is: the *net* flow.

The molecules that "reach" the ground are the ones that
were *already there* at ground level.

Hmmmm...It's not too out of line to think of air particles
at ambient temps as moving at the speed of sound.
Its those air "molecules" that carry sound waves longitudinally.
Air particles don't stay anywhere, in a manner of speaking...

Brian W