This is another run with slightly different periods and with a mix of NINO34 and SOI data.
I continue to be amazed that the solver converges to the same set of forcing functions independent of the time interval chosen. Is this the sign of a stationary, deterministic, and ergodic time series? Stationary means that the properties of the time series don't change over time. Ergodic means that the properties of the time series can be deduced from a sufficiently long sample.
So this is all consistent with ENSO as the forced response to (1) the angular momentum wobble of the earth and (2) that of the gravitational pull of the moon and sun. Together, those are the only significant behaviors that also show the same long term stationary characteristics, and the fact that they share the same frequencies with the ENSO result makes the model difficult to invalidate.
I am posting these ideas because I am trying to articulate my arguments for the upcoming AGU presentation. Based on all the research I have searched on this topic, it's still the case that no one is close to settling on this same mechanism. The sense that I get is that most climate scientists believe that ENSO is driven primarily by the direction of the currently prevailing wind. But what causes the wind direction? One can look at QBO, which I will be presenting as well and see that has a primarily lunisolar forcing mechanism, so that's in my favor.