Couple of recent posts where the harmonic series approximation for the ENSO forcing is reduced to a closed-form expression:

This simplification was also applied to QBO


These are timely findings, as the presentation was accepted to the AGU next month

[GC41B-1022: Biennial-Aligned Lunisolar-Forcing of ENSO: Implications for Simplified Climate Models]( ![mtg](

Check the sub-title :)