Oceanic Niño Index
Earth science
Also known as: ONI
Quick Summary
The Oceanic Niño Index (ONI) is a key measure in Earth science used to track the El Niño-Southern Oscillation (ENSO) phenomenon. It quantifies the departure from normal sea surface temperatures in the east-central Pacific Ocean.
- El Niño: Characterized by sea surface temperature increases of more than 0.5 °C (0.9 °F) for at least five consecutive overlapping three-month periods. This phase is associated with warmer waters in the Pacific and can lead to altered weather patterns globally, including increased rainfall in some regions and drought in others.12
- La Niña: Defined by sea surface temperature decreases of more than 0.5 °C (0.9 °F) for the same duration. La Niña typically brings opposite weather effects to El Niño, such as cooler-than-normal surface waters along the coast of South America and stronger trade winds.32
These ENSO variations play a significant role in interannual climate variability, influencing weather patterns worldwide.4
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