El Nino- La Nina

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Travis Watson February 28, 2013 Ecology Dr. G El Nino/La Nina and Affects on North American Weather How does El Nino form? What is El Nino? El Nino is an abnormal warming of surface ocean waters in eastern Pacific Ocean. El Nino events occur every 3 to 12 years. It is believed that the lack of severe storms in the North Atlantic is due to El Nino events. El Nino is part of the Southern Oscillation. Southern Oscillation is a see-saw pattern reversing the air pressure of the eastern and western Pacific. The warming of the ocean and reversal of the air pressure happen simultaneously. El Nino received its name because it usually happens around Christmas time and El Nino means “The Christ Child” in Spanish. The process of cold water becomes more intense causing the surface of the eastern Pacific to become cool. This is known as La Nina. These events has some affects on North American weather. Normal conditions, before El Nino events occur, strong trade winds move surface waters westward. As this occurs the water becomes warmer. When water becomes warmer it causes the air to rise and cool causing torrential rainfall. When El Nino occurs there a warm upper ocean layer, which is poor in nutrients and a cold lower ocean layer, which is rich in nutrients. The cold water is brought when the surface current flows westward in a process known as upwelling. Now, the trade winds for El Nino are weakened causing a reduction in the westward flow and upwelling is reduced. Rainfall follows the warm water to the east. The rainfall causes flooding in Peru and droughts in Australia and Indonesia. So, now in North America El Nino causes the hurricane season to diminish and the tornado season to be active. In the southern United States cooler and wetter weather is brought. Drier weather occurs in the Pacific Northwest. Southern California ends up having wetter weather. These effects
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