Causes and Process
(images from http://www.pmel.noaa.gov/tao/proj_over/tour/tao_tour.html)
El Niño
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.[8] 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.
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La Niña
La Niña is associated with cooler than average sea surface temperatures in the central and eastern tropical Pacific Ocean.
Opposite process of El Niño |