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NORMAL
Normally, trade winds blow warm surface water toward the western Pacific.
This causes the thermocline to rise near the surface in the eastern Pacific.
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Cold, nutrient-rich water wells up from the thermocline to the surface waters off the coast of Peru - good for fishing.
NOAA
This image shows normal sea surface temperature in the Equatorial Pacific Ocean in January 1997.
Notice the warm water is in a pool in the western Pacific Ocean.
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El Niño describes abnormal oceanic and atmospheric conditions.
First noticed off the coast of Peru around Christmas time, the condition was called El Niño referring to the Christ child.
EL NIÑO
When the Trade Winds falter, warm water piles up in the western Pacific about 1 & ½ feet higher than the average ocean surface
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El Niño’s weaker trade winds blow warm water eastward, across the equatorial region of the Pacific.
This depresses the thermocline across the Pacific, and stops upwelling.
NOAA
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Because warm water evaporates faster, the air fills with more water vapor and it produces more rain.
El Niño occurs primarily in the tropical Pacific Ocean but it affects global weather.
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LA NIÑA
When too much westerly wind blows surface water near the Americas, it has an effect on the weather that is often opposite to El Niño, called La Niña.
NOAA
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Comparison of El Niño and La Niña
• El Niño• La Niña
warmer ocean temperatures
occurs every 3-7 years
wetter than normal summers
weak trade winds
decreases hurricanes forming in N. Atlantic
colder ocean temperatures
frequency unknown
drier than normal summers
strong trade winds
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1997 was the warmest year of the century and the strongest El Niño in 40 years. Oddly, five of the century’s warmest years have been in the last decade.
NASA
