nad said:

> " so the QBO period seems rather strictly 2 years with some outliers which produce those average of 2.3 years (....as I keep saying)."

Possible, but I have been using a period of 2.33 years, which gives a locking in of 3 cycles per 7 years. But then again, there is clearly [jitter](http://en.wikipedia.org/wiki/Jitter) in the period about the 2.33 years, just as you say. If a period is longer in one cycle, it will catch up later. This is also known as frequency modulation (FM) about the mean period.

I have taken to use the 70 hPa measure of QBO because the jitter is stronger and so when I have to modulate the applied QBO frequency from cycle-to-cycle, it gives a much better fit in the model. Prior to that, I had been using the QBO at 20 hPa, which had less jitter, but also provided a poorer fit.

I will continue to better understand what the Chikamoto paper is stating, but in the meantime, I am doing my own thing. :)