El Niño

El Niño is the warm phase of the El Niño–Southern Oscillation, marked by unusually warm surface waters in the central and eastern tropical Pacific and shifts in atmospheric circulation.

El Niño–Southern Oscillation: A recurring coupled pattern of tropical Pacific ocean temperatures and atmospheric circulation with warm, cool, and neutral phases. El Niño is the warm phase of this wider ocean–atmosphere cycle.
Teleconnection: A statistical or physical connection between climate conditions in distant regions. El Niño's atmospheric effects link tropical Pacific warming to distant weather patterns.
El Niño de Navidad: A seasonal warm coastal current off Ecuador and Peru, named for its appearance around Christmas. The recurring coastal warming gave El Niño its name before scientists identified the basin-wide cycle.
Oceanic Niño Index: A three-month running average of sea-surface temperature anomalies in a central equatorial Pacific region used to monitor ENSO. It provides a standard measure for identifying and tracking El Niño episodes.
La Niña: The cool phase of ENSO, with unusually cold central and eastern tropical Pacific surface waters and strengthened trade winds. It often produces ocean and atmospheric anomalies opposite to those of El Niño.
Walker circulation: An east–west atmospheric circulation over the tropical Pacific, driven by differences in heating and pressure. El Niño weakens this circulation as eastern Pacific waters warm.
El Niño–Southern Oscillation teleconnections: Recurring climate connections through which ENSO influences weather in regions far from the tropical Pacific. These patterns describe how El Niño shifts rainfall and temperature around the world.
Peruvian anchoveta fishery: A large commercial fishery based on anchoveta populations in the southeastern Pacific. Fishermen's observations of changing catches helped draw attention to warm-water episodes.
Southern Oscillation Index: An index based on standardized sea-level pressure differences between Tahiti and Darwin, Australia. It tracks the atmospheric pressure component that often changes during El Niño.
ENSO-neutral: An ENSO state in which tropical Pacific ocean and atmospheric conditions do not meet El Niño or La Niña criteria. Neutral conditions provide the baseline against which El Niño anomalies are identified.

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