["Prominent precession‐band variance in ENSO intensity over the last 300,000 years"](https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL083410)

> "The simulated ENSO and AC amplitudes change in‐phase, and both have pronounced precession‐band variance (~21,000 years). The precession‐modulated slow (orbital time scales) ENSO evolution is dominated linearly by the change of the coupled ocean‐atmosphere instability, notably the Ekman upwelling feedback and thermocline feedback." in **Geophysical Research Letters**

How can they say this about orbital factors that impact ENSO via the thermocline and upwelling over thousands of years and yet neglect the orbital factors that clearly occur over the monthly cycle?

Part of the reason is that the orbital factors are all solar related, and so they preclude lunar forcing

> "First, we want to explore the ENSO response to the orbital forcing that includes full cycles of eccentricity (~100 ka), obliquity (~41 ka) and precession (~21 ka) (Berger and Loutre, 1991), with more extreme precessional forcing effects (modulated by a larger eccentricity compared to the last 21 ka). "

And this is how they can rationalize ignoring the short term scale

![](https://imagizer.imageshack.com/img921/7459/yRxe3s.png)

It looks as if they simplify that substantially differs from the shallow-water wave equation (i.e. Laplace's tidal equation) ansatz that I apply. They lose track of the non-linear terms and leave it in a form that essentially models a linearly sloshing thermocline see-saw. Moreover, they then conclude that it's too complex due to stratification. Yet if it's too complicated, how can they understand it enough to make extrapolations over a much longer time-scale?