The premise that I am working from is that the response follows from the solution to the wave equation for a largely unknown set of inputs.
This is a hard problem to discern what the inputs may be, but remember that we have two separate sets of measures that we can evaluate against : (1) the ENSO standing wave and (2) the QBO standing wave.
That's like having two different electrical circuits to discriminate against given a common unknown forcing. The additional constraints will narrow the forcing solution possibilities.
And there may be more of these measures available to check against -- for example, tidal gauge data shows a strong indicator for an ENSO signature
also here on Azimuth
That particular tidal gauge dataset is the first I tried since it appeared to be one of the longer time-series available. There lots more of these available.
My feeling is that this is a rich environment for analysis that curiously has not been tapped.