Good discussion topic. First of all, the "quasi" in quasi-biennial oscillations appears to be somewhat of a misnomer. The fundamental frequency in the QBO is locked into around 2.33 years. This is 3 complete cycles every 7 years. So it is not quasi-periodic as much as it is quasi=2 for the person that originally thought that 2.33 was similar to 2.
The fact that this fundamental period of 2.33 years is so strong allows me to back-propagate the values to times well before 1953, which is the date when measurements of the QBO were first undertaken.
I am not the first to notice how strong this 28 month period is:
Somebody else has created a time series that allows one to back-extrapolate to any year before 1953, and what this amounts to is the 28 month harmonic plus other Fourier series components. I can't find the ref at the moment, but I calculate the Fourier series myself because it is easy enough to construct and check for good correlation. This is what Mathematica's Find Formula discovers for 3 Fourier components (the highlighted component is close to the Chandler wobble beat frequency) :
I add a few more components to get the correlation coefficient higher, and that is the key to getting a good fit to ENSO. Unless this "jitter" or "frequency modulation" is included, the fit really won't work. That is possibly one of the reasons it has escaped the notice of researchers over the years. ( I built FM transmitters and radios as a teenager, so I know all about frequency modulation and knew that it could cause all the variation that was observed. I just didn't know how much better it would get the more I worked on it. )
I find it curious that the paper that Graham found claims that QBO isn't that predictable over the scale of much more than than 3 years:
> "We demonstrate predictability of the QBO extending more than 3 years into the future, well beyond timescales normally associated with internal atmospheric processes. "
What I notice is a difference in research done by climate scientists versus that done by geophysicists. Geophysicists aren't as afraid of making claims of determinism or periodicity, where climate scientists typically don't. I think this has a basis in the likelihood that climate scientists and meteorologists are taught to not make such strong claims in their forecasts. Why they write papers like this that don't point out the strong periodicity in the historical record is something I just can't understand.
Graham, I assume that is the same point that you "cannot make sense of" ?