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October, 20, 2019

Monitoring Indices

Concept

Originally the term El Niño applied to an annual weak warm ocean current that ran southwards along the coast of Peru and Ecuador at about Christmas time. However, over time the term has evolved and now refers to the warm and negative phase of the El Niño Southern Oscillation and is the warming of the ocean surface or above-average sea surface temperatures in either the central and eastern tropical Pacific Ocean. This warming causes a shift in the atmospheric circulation with rainfall becoming reduced over Indonesia and Australia, while rainfall and tropical cyclone formation increases over the tropical Pacific Ocean. The low-level surface trade winds, which normally blow from east to west along the equator, either weaken or start blowing from the other direction.

Occurrences

El Niño events are thought to have been occurring for thousands of years. The strongest El Niño events were recorded in the years 1982-83, 1997–98 and 2014–16.Since 2000, El Niño events have been observed in 2002–03, 2004–05, 2006–07, 2009–10 and 2014–16. Major ENSO events were recorded in the years 1790–93, 1828, 1876–78, 1891, 1925–26, 1972–73, 1982–83, 1997–98, and 2014–16. Typically, this anomaly happens at irregular intervals of two to seven years, and lasts nine months to two years. The average period length is five years. When this warming occurs for seven to nine months, it is classified as El Niño "conditions"; when its duration is longer, it is classified as an El Niño "episode"

Effects on the global climate

El Nino affects the global climate and disrupts normal weather patterns, which as a result can lead to intense storms in some places and droughts in others.

Regional impacts

During El Niño events, the shift in rainfall away from the Western Pacific may mean that rainfall across Australia is reduced. In Africa, East Africa, including Kenya, Tanzania, and the White Nile basin  experiences, in the long rains from March to May, wetter-than-normal conditions. Conditions are also drier than normal from December to February in south-central Africa, mainly in Zambia, Zimbabwe, Mozambique, and Botswana. the majority of Canada generally has a milder than normal winters and springs, with the exception of eastern Canada where no significant impacts occur. The effects of El Niño in South America are direct and stronger than in North America. An El Niño is associated with warm and very wet weather months in April–October along the coasts of northern Peru and Ecuador, causing major flooding whenever the event is strong or extreme.

 

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