Characteristics of El Niño. It occurs in the Pacific basin every 2 to 9 years It usually starts during the North winter Once established, it last until the first half of the following year It exhibits phase-locking in annual cycles
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Abnormalities such as:
-delayed onset of the rainy season
-early termination of the rainy season
-weak monsoon activity (isolated heavy downpours with short
-weak tropical cyclone activity
La Nina is an atmospheric interaction between the ocean/air interfaces. Temperatures in the ocean affect the air above it, therefore creating shifts in climate that can have both regional and global consequences.
During La Niña years, the trade winds are unusually strong due to an enhanced pressure gradient between the eastern and western Pacific. As a result, upwelling is enhanced along the coast of South America, contributing to colder than normal surface waters over the eastern tropical Pacific and warmer than normal surface waters in the western tropical Pacific.
The global wind pattern is also known as the "general circulation," and the surface winds of each hemisphere are divided into three wind belts:
•Polar Easterlies: From 60-90 degrees latitude.
•Prevailing Westerlies: From 30-60 degrees latitude (aka Westerlies).
•Tropical Easterlies: From 0-30 degrees latitude (aka Trade Winds).