what causes this?

[deek]

I'm talking about the flame pattern out of the afterburner? I guess you could call it a diamond pattern.

http://www.airliners.net/photo/Roma...y_views_desc_&prev_id=1463400&next_id=1463595


http://www.airliners.net/photo/Romania---Air/Mikoyan-Gurevich-MiG-21MF-Lancer/1463946/L/

 

[Orange Anchor]

http://en.wikipedia.org/wiki/Shock_diamond

http://www.aerospaceweb.org/question/propulsion/q0224.shtml

 

[c172captain]

Of course it'd have a cool name like "Shock Diamond"