Walker circulation, thermocline depth, and coupled ocean-atmosphere feedback
Neutral
1.0×
La NiñaNeutralEl Niño
In El Niño (warm phase), the trade winds weaken, warm water sloshes east, the thermocline flattens, and the Walker circulation reverses.
In La Niña (cool phase), trades strengthen, warm pool deepens in the west, and upwelling intensifies off South America.
The cycle repeats every 2–7 years through Bjerknes positive feedback.