Identify the mechanisms driving Normal, El Niño, and La Niña conditions.
Explain trade wind weakening or strengthening and its effect on equatorial ocean currents.
Connect upwelling suppression to ecological impacts (fisheries collapse).
Key Metric: Oceanic Niño Index (ONI)
The ONI tracks 3-month average sea surface temperature anomalies in the Niño 3.4 region (equatorial Pacific).
El Niño: ONI ≥ +0.5°C La Niña: ONI ≤ -0.5°C
Why It Matters
ENSO is the most important coupled ocean-atmosphere phenomenon on Earth. Alterations to Pacific water temperatures reorganize global weather patterns, causing droughts in Australia and floods in Peru.
Tags
APESClimateOcean CurrentsEcology
Equatorial Pacific Cross-Section View
StateNormal Conditions
Trade WindsStrong East-to-West
Upwelling (Peru)Active
🌏 Australia / Indonesia
South America 🌎
Global Climate Phase
Phenomenological Effects
Oceanography: Strong Equatorial trade winds push warm surface water towards Australia, piling it up. Deep, cold, nutrient-rich water rises off the coast of South America to replace it (Upwelling).
Atmosphere & Weather: Warm pool in the West causes convective rising air, leading to heavy rainfall in Indonesia. Descending dry air over the Eastern Pacific limits rain in South America.
Ecology: Upwelling brings massive amounts of nutrients to the photic zone. Phytoplankton bloom, supporting a massive anchovy fishery industry in Peru.
Quick Quiz
During El Niño, why does the anchovy fishery off the coast of South America collapse?