PaulP: "QBO has a unique standing-wave mode as it has a wavenumber index of 0"
Again, a non-relativistic (non-Galilean) assertion. I had already given a relativistic (more realistically physical) version-
"QBO wave-number is properly two non-zero angular wavenumbers (for easterly and westerly motions, respectively) relative to Earth Frame. Precession, terrain, Coriolis, sunspot cycles, ENSO, and other variables, cause calculable QBO wavenumber variation. AO and AAO most closely approximate wavenumber zero, as zonal (symmetric) flows."
Also, there are the travelling-wave modes in these major Oscillations. They really are complex sequences of evolving wave-packets. Idealized over-simplification misses a lot of action. Feynman Diagramming these extreme-scale phonon cycles would be really cool.