OSU OC 103 - e-OC103-Lesson14-1 (5 pages)

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OC103 Lesson 14 El Ni o and La Ni a An unusual oceanic phenomenon called El Ni o occurs every 2 10 years in the tropical Pacific Ocean and has widespread affects on global weather patterns El Ni o effects in the western U S include unusually wet stormy winters in southern Oregon and northern California to the point of sometimes causing heavy flooding and coastal erosion and unusually dry winters in northern Oregon and Washington This lesson covers what El Ni o is how it happens and what some of its effects are As scientists study El Ni o more and collect more data it is becoming clear that El Ni o is an important climate feature El Ni o related weather sometimes leads to damage that costs hundreds of millions of dollars and affects several important sectors of the economy It is an example of a coupled ocean atmosphere phenomenon and demonstrates how the ocean atmosphere and climate are interconnected El Ni o Unusual oceanic phenomenon abnormally warm surface water in the equatorial Pacific Ocean First described by a Peruvian scientist in 1891 based upon accounts by local fisherman along the coasts of Ecuador and Peru they named it The Christ Child because they often first noticed it there around Christmas time Characteristics o Normally starts in western tropical Pacific and develops progressively eastward o Often results in natural disasters flood droughts fires but is also thought to suppress hurricane development in the tropical Atlantic Ocean o Occurs every 2 10 years the most recent and severe events were in 1953 1957 58 1965 1972 73 1976 77 1982 83 1991 92 1997 98 2002 03 2009 10 and 2015 16 o The U S National Weather Service s official definition of an El Ni o requires tropical Pacific surface ocean water temperatures at least 0 5 C above normal for 5 consecutive months o Moderate El Ni os in 2006 and 2009 may have been part of the reason why the 2006 and 2009 Atlantic hurricane seasons were so mild and the Pacific hurricane typhoon seasons were so severe We don t know everything about El Ni os yet We can t really predict one yet although we now know some early warning signs to watch for Abnormal Wind and Ocean Conditions of El Ni o In a normal year in the Pacific strong east to west tradewinds near the equator push warm surface water to the west see figure below This allows cold deeper water to upwell rise to the surface along the South American coast This upwelling brings nutrients from below up into the photic zone where they can be utilized by microscopic algae The rich fishing industry off the west coast of South America is ultimately supported by this upwelling of nutrients Normal year In an El Ni o year the tradewinds weaken or fail and tropical winds along the equator reverse blowing toward the east instead of to the west see figure below