El Niño and La Niña – trade winds, upwelling and the Southern Oscillation
GeographyWeather & ClimateAges 15–16
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Sign in to play
A cross-section of the equatorial Pacific from Indonesia to Peru. Drag the trade-wind strength: strong winds pile warm water in the west, tilt the thermocline and bring cold, nutrient-rich water up off Peru (La Niña); weaker winds let the warm pool spread east, move the rain clouds to the central Pacific, weaken upwelling and warm the sea off Peru (El Niño). Readouts give the Niño 3.4 temperature, the Southern Oscillation Index (SOI) from Tahiti and Darwin pressure, thermocline depth, coastal sea temperature off Peru and the anchoveta catch. A map shows sea-surface temperature anomalies, the Humboldt Current and rainfall compared with normal in Indonesia, eastern Australia, coastal Ecuador and Peru and Brazil. The Cycle view runs a recharge-oscillator model in which El Niño and La Niña alternate every few years.
Lesson: El Niño, La Niña and the Southern Oscillation (ENSO)
What it shows
ENSO is the largest year-to-year swing in Earth's climate. Along the equatorial Pacific, the trade winds blow warm surface water west, so the thermocline is deep near Indonesia and shallow near Peru, where cold water wells up along the Humboldt Current. In this simplified model the wind strength sets the tilt of the thermocline and the strength of upwelling; sea-surface temperature mixes the warm pool with upwelled water. Rain clouds form over the warmest water. Rainfall responses are typical ENSO-season patterns. The Cycle view uses Jin's recharge oscillator with random westerly wind bursts.
How to use
In Pacific cross-section, drag Trade-wind strength and watch the thermocline, the clouds, the fish and the map; press Record to add a row to the table and the graph. Find the wind strength at which the Niño 3.4 anomaly reaches +0.5 °C. In ENSO cycle, set Wind–ocean coupling and Westerly wind bursts, press Run and read the events table and the time series.
Parameters you can change
- View Pacific cross-section, ENSO cycle
- Trade-wind strength 20–160 % of normal
- Wind–ocean coupling 0–2
- Westerly wind bursts 0–3
Questions to explore
- Why does the sea off Peru warm up when the trade winds weaken?
- Why does Peru's anchoveta catch fall sharply in an El Niño year?
- What weather does eastern Australia usually get when the SOI stays strongly negative?
