This is a quick rough and ready analysis of an QBO data since Paul Vaughan asked. Here are all the things you never wanted to know.
QBO ( Quasi-Biennial Oscillation) is a strange entity, wind direction alternates. The data is an index, artificial computation and in this case part of a reanalysis. This article might add some insight http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo
A problem I see with simple data such as at one pressure level and location is the many other changes over time. Perhaps the pressure level should vary a little. It’s a multi-dimension entity anyway.
I’m taking it as-is with no more comment.
Figure 1, straight plot of monthly data, which runs from 1948. No units are given so assume metres/second. Data used
The author has several bespoke software works useful for analysis, in C, unpublished so reproducing this work would be difficult.
On considering the data the period before 1970 is ignored. There is no information on technology changes or data reliability.