Annually Modulated Pacific Subtropical Highs Pace the ENSO Cycle: A Hierarchical Framework from Earth Rotation to Atmosphere-Ocean Dynamics

Abstract

The El Nino-Southern Oscillation drives Earth's dominant interannual climate signal, yet what initiates an event and what ends it remain incompletely understood. Here we show that anomalies of the eastern Pacific subtropical high (EPSH) belts, marched through the year by the annual cycle, precede and govern the equatorial zonal wind near the dateline, which sets subsequent sea surface temperature evolution. The Northern Hemisphere ridge triggers events in boreal spring, the Southern Hemisphere ridge sustains them in austral spring, and their synchrony decides ENSO diversity. Preceding the ridges lies a sub-annual oscillation in Earth's rotation rate (length of day, 0.5 to 1 yr band) that redistributes atmospheric mass poleward three times once its phase aligns with the annual cycle, in August, in December, and in the following May, each displacement carrying the response further east and poleward until the significant centers overlie the ridges themselves. Crucially, this band is deaf to ENSO: its cross-correlation with NINO3 never exceeds 0.05 at any lag, whereas the classical ENSO-driven rotation response resides in the 2 to 10 yr band at 0.40. The band therefore reads forward, and partial correlation identifies the EPSH as the conduit: the direct path from rotation to ocean vanishes once the ridges are held fixed. Complete by the July preceding the event year, the index fixes the phase of the coming event fourteen to seventeen months ahead, though not its amplitude. At maturity the event reorganizes the Hadley and Walker circulations into the Mirror-SIGMA pattern, disrupting the upstream chain and closing the cycle.