"Kev" wrote in message
ups.com...
On Apr 16, 3:59 pm, Tom L. wrote:
The big question is "why does the wake turbulence descend?"
Is the air volume inside the vortices denser than surrounding air?

Found it, Tom. Ref:

http://www.airpower.maxwell.af.mil/a...ug/carten.html

"Cruise altitude vortices usually level off at about 1000 feet below
the altitude of the aircraft as their density comes into equilibrium
with that of the surrounding air. Decay processes then take over. "


Don't underestimate the value of the words "usually" and "about" in that
sentence. You are still trying to absolutely describe something that is very
dynamic.