I just wanted to remark for completeness:
>Moreover it looks to me as if there is also an annual oscillation contained in the signal, like there seems to be always a little “bump” on the downslide between peaks. This bump is sometimes rather high (“a small peak”, an “extrasystole”) and seems to lead in that case to a lagging behind of the biannual signal peak. This happens slightly before the year 63 (almost nonvisible) , before 65 the “extrasystole” is comparibly big leading to the lag between 65 and 67 the small peak behind 67 would have been the original 67 peak if there wouldn’t have been the lagging, in 69 the signal is again in sync, before 77 an extrasystole is again leading to a lagging, again before 79, leading to a lagging, the small peak at 81 would again be the peak at 81 if not for the lagging, here the signal has now a 90 degrees phaseshift, i.e. the beat is quite out of sync, it catches though up again in 85, in 87 small extrasystole with small lagging, in 89 big extrasystole, signal again out quite out of sync, catches up in 97, extrasystole before 01, 03 and 05, out of sync until it “catches up again” in 2013. If there is no extrasystole in 2014 I conjecture that the QBO index will peak again in summer 2015.
Likewise I wrote here:
>Nevertheless as described above and in the previous comments the QBO appears to me to be a consequence of a more regular pattern and thus irregularities might happen like it could happen that some blotches merge etc. One would need thus to look at the respective years, where the exact 2-year pattern breaks down, like wether there were vulcano’s etc. and in particular one should look at this together with the SOI.
In that image the regular odd year pattern is disturbed for the years (63) 65, 67, (77), 79,81,(83),(89),91,(03),05,07,09,(11)
the years in brackets are years where the QBO is only "somewhat" out of sync, this is usually a year before or after a series of "out of sync" signals.
So the pattern of the "extrasystoles" is also directly visible in the images.