In article ,
Beryl wrote:

Alan Baker wrote:
...
First of all, the downward motion of the vortex clearly carries right
out the bottom of the frame.
Are you impaired? The airplane is approaching the camera. The camera is
looking up at the airplane. The bottom of the frame contains the distant
background. Objects farther than the airplane appear lower in the frame.
If the camera was above the approaching airplane and looking down at
it, distant objects would appear higher in the frame than the airplane.

None of which refutes what I said.

Oh, it was simply interesting to you that the vortex goes off into the
distance, right out the bottom of the picture.

No. That shows that the air continues to move downward far below the
small portion of the vortex which is moving up.

The net movement of the air after the plane's passing must be downward,
because the plane is exerting a force on the air.

Force is a change of momentum with respect to time.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg