Walker circulation

Walker circulation is the large-scale atmospheric circulation cell that spans the tropical Pacific Ocean, named after Gilbert Walker who identified it in the 1920s while searching for correlations between Indian monsoon rainfall and global pressure patterns. In the Pacific, the Walker circulation manifests as rising motion over the warm western Pacific (Indonesia), westward flow aloft, descending motion over the cool eastern Pacific (South America), and easterly surface trade winds completing the loop. The circulation is driven by the east-west sea surface temperature gradient and is the atmospheric component of the El Niño-Southern Oscillation coupled system. When the Walker circulation weakens, warm water sloshes eastward and an El Niño event develops; when it strengthens, La Niña intensifies.

The Walker circulation is not an isolated cell. It connects to the Hadley cell through the ascending branch in the western Pacific, and its strength is modulated by the Indian Ocean Dipole and the Madden-Julian Oscillation. From a systems perspective, the Walker circulation is a feedback amplifier: it converts temperature gradients into wind anomalies, and the wind anomalies in turn maintain the temperature gradient. The circulation is not merely a response to ocean conditions. It is an active participant in their creation.