Editing Atmospheric circulation (section)

=== Walker circulation ===
{{Main|Walker circulation}}
The Pacific cell is of such importance that it has been named the '''Walker circulation''' after [[Sir Gilbert Walker]], an early-20th-century director of British observatories in [[India]], who sought a means of predicting when the [[monsoon]] winds of India would fail. While he was never successful in doing so, his work led him to the discovery of a link between the periodic pressure variations in the [[Indian Ocean]], and those between the eastern and western Pacific, which he termed the "[[Southern Oscillation]]".

The movement of air in the Walker circulation affects the loops on either side. Under normal circumstances, the weather behaves as expected. But every few years, the winters become unusually warm or unusually cold, or the frequency of [[hurricane]]s increases or decreases, and the pattern sets in for an indeterminate period.

The Walker Cell plays a key role in this and in the [[El Niño]] phenomenon. If convective activity slows in the Western Pacific for some reason (this reason is not currently known), the climates of areas adjacent to the Western Pacific are affected. First, the upper-level westerly winds fail. This cuts off the source of returning, cool air that would normally subside at about 30° south latitude, and therefore the air returning as surface easterlies ceases. There are two consequences. Warm water ceases to surge into the eastern Pacific from the west (it was "piled" by past easterly winds) since there is no longer a surface wind to push it into the area of the east Pacific. This and the corresponding effects of the Southern Oscillation result in long-term unseasonable temperatures and precipitation patterns in North and South America, Australia, and Southeast Africa, and the disruption of ocean currents.

Meanwhile, in the Atlantic, fast-blowing upper level Westerlies of the Hadley cell form, which would ordinarily be blocked by the Walker circulation and unable to reach such intensities. These winds disrupt the tops of nascent hurricanes and greatly diminish the number which are able to reach full strength.<ref>{{Cite web|title=The Walker Circulation: ENSO's atmospheric buddy {{!}} NOAA Climate.gov|url=https://www.climate.gov/news-features/blogs/enso/walker-circulation-ensos-atmospheric-buddy|access-date=2020-10-03|website=www.climate.gov}}</ref>

==== El Niño – Southern Oscillation ====
{{Main|El Niño-Southern Oscillation}}

''El Niño'' and ''La Niña'' are opposite surface temperature anomalies of the Southern Pacific, which heavily influence the weather on a large scale. In the case of El Niño, warm surface water approaches the coasts of South America which results in blocking the upwelling of nutrient-rich deep water. This has serious impacts on the fish populations.

In the La Niña case, the convective cell over the western Pacific strengthens inordinately, resulting in colder than normal winters in North America and a more robust cyclone season in [[South-East Asia]] and [[Eastern Australia]]. There is also an increased upwelling of deep cold ocean waters and more intense uprising of surface air near South America, resulting in increasing numbers of drought occurrences, although fishermen reap benefits from the more nutrient-filled eastern Pacific waters.