NOAA sea-surface temperature anomaly map with warmer-than-average water across the equatorial Pacific in late 2015.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Ocean depths ×10,000. 15,000 km section. atmospheric loop schematic.

Neutral · thermocline west 180 m / east 60 m. Gold: ideal thermocline; amber: warmer upper water; blue: colder water.

How to read these results

ENSO selects a prescribed state. Play moves illustrative tracers, not years or a forecast. Teleconnections change probabilities; they do not determine a particular UK winter.

ENSO and the Walker cell

Compare normal Pacific conditions with El Niño and La Niña, and explain how changes in winds and ocean temperature affect rainfall.

Drag to rotate. Hold Ctrl and scroll to zoom, or pinch on a touch screen.

Why it happens

Across the tropical Pacific, trade winds, warm surface water and the thermocline interact. El Niño and La Niña describe departures from the usual coupled ocean–atmosphere pattern.

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NOAA, 11 October–7 November 2015: positive sea-surface temperature anomalies extend across the central and eastern equatorial Pacific during El Niño.

Try a comparison

Move to El Niño and compare eastern temperature and thermocline depth. Compare La Niña and explain the stronger contrast.

Reading the result

The selected states illustrate these relationships; their effects on weather vary between events and places.

A common misunderstanding

El Niño causes the same weather in every affected place during every event.

ENSO changes tropical Pacific ocean and atmospheric conditions, influencing weather probabilities in many regions. The response depends on season, event strength and other climate conditions. A regional tendency towards wetter or drier weather is not a guarantee for every location, day or event.

Cases

Exam language

Walker cell

A simplified east–west tropical Pacific circulation, with rising air over warmer water and sinking air over cooler water. Its near-surface branch is linked to the trade winds. Changes in this circulation are part of ENSO.

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Sentinel-6 mapped sea-surface height anomalies during La Niña in January 2025. Ocean–atmosphere coupling changes the Walker circulation and can influence distant weather through teleconnections; these atmospheric links are not directly pictured.

ENSO

The El Niño–Southern Oscillation is a coupled pattern of ocean and atmospheric variability in the tropical Pacific. Its warm and cool phases alter sea-surface temperature, trade winds and rainfall. These phases influence weather probabilities rather than prescribing every local event.

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NOAA, 11 October–7 November 2015: positive sea-surface temperature anomalies extend across the central and eastern equatorial Pacific during El Niño.

El Niño

The warm phase of ENSO, marked by unusually warm sea-surface temperatures in the central and eastern equatorial Pacific and coupled atmospheric changes.

La Niña

The cool phase of ENSO, with unusually cool central and eastern equatorial Pacific surface waters and associated changes in tropical winds and rainfall.

Warm pool

A region of unusually warm tropical surface water. In the Pacific, its extent and position change with winds and ENSO.

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AMSR-E, 19 October 2004. This warm-pool region was cooler than its long-term average. Colours show temperature anomalies, not absolute water temperature; a negative anomaly does not mean the water is cold in absolute terms.

Teleconnection

A statistical relationship between climate or weather variations in distant regions, such as the influence of ENSO on rainfall probabilities.

Upwelling

The movement of deeper water towards the surface, often driven by winds that move surface water away or by large-scale ocean circulation.

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Aqua MODIS, 5 May 2020. Upwelling in the Canary Current system supplies nutrients off Mauritania. The visible green water contains phytoplankton and sediment; it is not a temperature map.

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