Walker circulation

The Walker circulation is an east–west atmospheric circulation across the tropical Pacific, with rising air over warm western waters and sinking air over cooler eastern waters. Its strength varies with Pacific sea-surface temperatures and helps shape tropical rainfall and climate.

Trade winds: Persistent easterly winds that blow across the tropics toward the equator. They push warm surface water westward and help maintain the circulation’s temperature contrast.
El Niño: A periodic warming of the central and eastern tropical Pacific associated with changes in ocean and atmospheric circulation. It weakens the usual Pacific Walker circulation and shifts tropical rainfall eastward.
Gilbert Walker: A British physicist and statistician who studied global atmospheric pressure and rainfall patterns. His analysis of pressure variations across the tropics revealed the circulation’s large-scale relationships.
Climate model: A numerical representation of the climate system based on physical laws and parameterized processes. Models are tested on whether they reproduce the Walker circulation’s observed structure and variability.
Pacific warm pool: A region of exceptionally warm surface water in the western tropical Pacific. Its warm, moist air rises in the circulation’s ascending branch.
La Niña: A periodic cooling of the central and eastern tropical Pacific associated with changes in ocean and atmospheric circulation. It commonly strengthens the Walker circulation and intensifies its west–east contrasts.
Southern Oscillation Index: A standardized measure of the pressure difference between Tahiti and Darwin, Australia. It provides an observational measure of the pressure seesaw tied to Walker circulation.
Seasonal forecasting: Prediction of climate conditions over periods from months to about a year. Forecasts use expected circulation changes to anticipate shifts in tropical rainfall.
Thermocline: A layer in the ocean where temperature decreases rapidly with depth. It lies deeper in the western Pacific and shallower in the east, reinforcing surface-temperature differences.
Southern Oscillation: A recurring variation in atmospheric pressure between the western and eastern tropical Pacific. Its pressure seesaw tracks major changes in the Walker circulation.

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