Suppose there was jitter on a periodic waveform that tended to align the peaks toward 1/2 year dates. In terms of a frequency power spectra, this jitter will not change the positions of the component peaks, but will impact their magnitude. As long as the jitter doesn't have long-range order, this is a commonly used approximation.

This paper [1] shows a "re-analyzed" Kelvin wave that shows jitter that also appears to align on 2, 2.5, and 3 year intervals, but staying near the 2.33 periodicity over the long term. You can see that with the 7 year intervals
![kelvin](http://imageshack.com/a/img673/5980/1f0egq.png)

[1]Y.-H. Kim and H.-Y. Chun, “Momentum forcing of the quasi-biennial oscillation by equatorial waves in recent reanalyses,” Atmospheric Chemistry and Physics, vol. 15, no. 12, pp. 6577–6587, 2015.

Note the comment #6 near the top of this thread, where I stated the groupings of (2+2+3) + (2+2.5+2.5) + (2+2+3), which do appear above! (not in that order though)

I think this supports the idea that the 2.33 year period is emerging as a result of the constructive interference of the Draconic tidal cycle with the yearly cycle. There could be as well interference with the 1/2 year cycle.

Yet since the aliased Draconic period is 2.368 years as opposed to 2.333 year, this alignment will gradually get out of sync after~29 cycles. That is if we believe that 2.368 is the actual forcing driver.

But if this yearly interference didn't exist, the lunar Draconic forcing would probably not have emerged. That's why the theory has some staying power, even in the light of these seasonal barriers.