The Walker circulation is made up of trade winds blowing from east to west across the tropical Pacific Ocean (blue arrow), bringing moist surface air to the west. In the western tropical Pacific, the moist air rises, forming clouds. The rising air becomes drier because most of its moisture falls to the surface as rain. Winds blow from west to east, moving the now drier air toward South America. The dry air returns back to the surface in the eastern tropical Pacific, completing the loop.
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Image courtesy of NOAA Geophysical Fluid Dynamics Laboratory
The Walker circulation is an ocean-based system of air circulation. This system influences weather on the Earth. Normally, the warm, wet western Pacific Ocean is under a low pressure system, and the cool and dry eastern Pacific Ocean is under a high pressure system. This causes surface air to move east to west, from high pressure in the eastern Pacific to low pressure in the western Pacific. Higher up in the atmosphere, winds flow from west to east, and this completes the loop.
The Walker circulation is part of the normal weather conditions in the tropical Pacific Ocean. Normally, the western Pacific has warm, wet weather and eastern Pacific has cool, dry weather.
The Walker circulation changes every few years, and this changes the weather. This is part of the El Niño-Southern Oscillation (ENSO). When the Walker circulation weakens, it is called El Niño. When the Walker circulation is very strong, it is called La Niña. El Niño and La Niña impact the weather in North and South America, Australia, and Southeast Africa. El Niño and La Niña can cause flooding, droughts, and increases or decreases in the number of hurricanes that form.
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