A great example of this is when the space shuttle lands, particularly at
Edwards (at KSC it tends to be humid so water vapor forms in the vortices
and masks the refraction). I've noticed it a few times and it is mainly
visible in video pointed right down the runway. Super high wing loading, I
would guess. I searched for a while but could only come up with one decent
video showing the phenomena. Pictures don't really demonstrate it. This
video is in quicktime *.mov format, so my apologies if you can't view it.

http://www.fotosearch.com/comp/FIL/FIL101/EV0116.mov

The physics of it are just those of compressible flow. Change in density
leads to change in the index of refraction of the gas. Visible, as someone
else said, via the Schlieren optical system often used in
transonic/supersonic wind tunnels. I've seen such a setup in action at the
supersonic tunnel at my school. Pretty cool stuff.

http://www.ae.su.oz.au/aero/super2d/ssflow3.html
http://web.mit.edu/edgerton/people/v...schlieren.html


-Tony Goetz
Rocket scientist in training.