What's interesting about the common tidal forcing of (AO, NAO, PNA, SAM) is that there is a distinct visible period in the time-series which is the lunar *tropical* month (27.321582 days) aliased against the annual signal.

![forcing](https://imagizer.imageshack.com/img924/2990/7IYddU.png)

1/(365.242/(27.321582)-13) = 2.72 years

For the QBO, the forcing and response are very close to each other (due to the low LTE factor) and the tidal forcing is the lunar *draconic* month (27.2122 days) aliased against the annual signal. This gives the measured QBO periodicity of:

1/(365.242/(27.2122)-13) = 2.37 years

There are many papers suggesting that there is a connection between QBO and polar behavior, but it is not always there. The wavenumber 0 symmetry of the QBO precludes any tropical (synodic) dependence so the cycle is draconic while the the other indices require a tropical dependence as they are geospatially specific. The two distinct cycles will go in and out of sync gradually with an 18.6 year cycle.

One such paper from earlier this year claiming the teleconnection:
[Observed and Simulated Teleconnections Between the Stratospheric Quasi‚ÄźBiennial Oscillation and Northern Hemisphere Winter Atmospheric Circulation](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JD029368)