PaulP: " I could write rings around...heuristic logic junk"

That would indeed be impressive. Never forget; Scientific Method is the Mother of applied Heuristic Logic.

Good Luck Paul, with your quest to better explain "long-period tidal forcing cycles in geophysical behaviors". I'm sorry if it was unwelcome to heuristically develop the sensor crosstalk supplementary hypothesis to forcing, as an explanation refinement of the lunisolar signal in ENSO-QBO data.

Remember, ENSO-QBO Deterministic Chaos is deterministic and predictable, to the extent a sufficient model and computing resources allow. Partial Tidal Forcing of ENSO-QBO does not predict the Geophysical Chaos component, which still will be, at current best, Ensemble-Modeled, like multi-physics weather prediction generally.

645 posts over seven years was a decent run for a Forum topic. Thanks for the great information.

This MIT video courseware on Harmonic Forcing is helpful to me in getting closer to quantifying the degree of ENSO-QBO forcing:

Here is a nice clue; some quantification of an ENSO-QBO correlation, "The quasi-biennial ENSO rhythm appears to be a harmonic oscillation in equatorial Pacific atmosphere-ocean system, and it was in sync with the QBO in 1879-99 and 1963-83". That's 40 years of correlation out of around 150 years. If this data were part of a highly periodic sequence (not likely), another twenty years of synchrony would begin around 2047.

We can reason that ENSO-QBO are either weakly coupled to each each other's inherent 1st harmonic, or weakly forced by a common input, or a bit of both. The weakness of the correlation is a rough measure of the weakness of forcing or chance resonance. Supposed resonance occurs when ENSO periods trend shorter. Some amount (>0) of Lunisolar crosstalk on the modern sensor-array data, and even on the geological record, is expected.

A further ENSO-QBO-Lunisolar possibility comes to mind. Jupiter's QQO QBO-analog suggests this oscillation will occur by Coriolis excitation and thermal convection, without need for a comparatively massive lunisolar tidal factor. Most geophysicists see ENSO as strongly Coriolis- and thermal-driven, and chaotic to the degree its only quasi-periodic. Its plausible that Lunisolar Tidal Input, when the set-up is right, actually tips ENSO-QBO chaos into action, as well as contributing occasional weak forcing, and superposing crosstalk signal on the data. It can do all three effects; Earth is sufficiently complex.

[Guilyardi et al, 2009] gives a grand overview of ENSO science predictive complexities-