El Niño – Southern Oscillation 🌊
A delayed-oscillator model of the equatorial Pacific. Warm water sloshes east and west; the thermocline tilts; the ocean cycles between El Niño and La Niña.
State
ONI (SST anomaly)0.00 °C
PhaseNeutral
Cycle period– yr
Months in phase0
Simulated year0.0
The delayed oscillator: dT/dt = a·T − b·T(t−τ) − ε·T³. The positive Bjerknes feedback (a) amplifies the eastern-Pacific SST anomaly T, while equatorial waves reflecting off the western boundary return with a delay τ and reverse the sign (−b·T(t−τ)), producing the ~2–7 year ENSO cycle. The cubic term ε bounds growth. ONI > +0.5 °C marks El Niño; < −0.5 °C marks La Niña.