page_title: Walker circulation
section_title: Oceanic effects
hierarchical_section_title: Walker circulation / Oceanic effects
caption_attribution_description: English: Average Pacific Ocean sea surface temperatures. The normal ENSO western Pacific warm water pool is present. The wintertime effect of mountain jets are apparent on the west side of Central America.
context_page_description: The Walker circulation, also known as the Walker cell, is a conceptual model of the air flow in the tropics in the lower atmosphere. According to this model, parcels of air follow a closed circulation in the zonal and vertical directions. This circulation, which is roughly consistent with observations, is caused by differences in heat distribution between ocean and land. It was discovered by Gilbert Walker. In addition to motions in the zonal and vertical direction the tropical atmosphere also has considerable motion in the meridional direction as part of, for example, the Hadley Circulation.
  The term "Walker circulation" was coined in 1969 by the Norwegian-American meteorologist Jacob Bjerknes.
context_section_description: The Walker Circulations of the tropical Indian, Pacific, and Atlantic basins result in westerly surface winds in Northern Summer in the first basin and easterly winds in the second and third basins.  As a result, the temperature structure of the three oceans display dramatic asymmetries.  The equatorial Pacific and Atlantic both have cool surface temperatures in Northern Summer in the east, while cooler surface temperatures prevail only in the western Indian Ocean. These changes in surface temperature reflect changes in the depth of the thermocline.
  Changes in the Walker Circulation with time occur in conjunction with changes in surface temperature.  Some of these changes are forced externally, such as the seasonal shift of the Sun into the Northern Hemisphere in summer.  Other changes appear to be the result of coupled ocean-atmosphere feedback in which, for example, easterly winds cause the sea surface temperature to fall in the east, enhancing the zonal heat contrast and hence intensifying easterly winds across the basin. These enhanced easterlies induce more equatorial upwelling and raise the thermocline in the east, amplifying the initial cooling by the southerlies. This coupled ocean-atmosphere feedback was originally proposed by Bjerknes. From an oceanographic point of view, the equatorial cold tongue is caused by easterly winds. Were the earth climate symmetric about the equator, cross-equatorial wind would vanish, and the cold tongue would be much weaker and have a very different zonal structure than is observed today.
  The Walker cell is indirectly related to upwelling off the coasts of Peru and Ecuador. This brings nutrient-rich cold water to the surface, increasing fishing stocks.
caption: Average equatorial Pacific temperatures