Equatorial Pacific — SST anomaly & trade winds
ENSO Index time series
State
ENSO index (ONI)
0.00 °C
Phase
Neutral
Trade-wind strength
100%
Simulated year
0.0
Controls
Model: dT/dt = a·T − b·T(t−τ) − ε·T³. Weaker trade winds let warm water pool in the
east (positive Bjerknes feedback, a); a delayed reflected wave (τ ≈ 5 months) eventually
reverses the sign. ONI > +0.5 °C = El Niño (warm, weak trades); < −0.5 °C = La Niña
(cool, strong trades).