Topic 12El Niño

GEOL 2503

Introduction to Oceanography

El Nio

• A disruption of the ocean-atmosphere system in the tropical Pacific

• Has important consequences for weather around the globe

• Frequently occurs around Christmas

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Normal conditionsStrong trrade winds-

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El Niño resources

• NOAA: http://www.elnino.noaa.gov/

• See animations at:– http://esminfo.prenhall.com/science/

geoanimations/animations/26_NinoNina.html

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El Niño Characteristics

• Normally develops in W. tropical Pacific• Often results in natural disasters• Occurs every 2 to 10 years• Most recent and severe events in 1953,

‘57-’58, ‘65, ‘72-’73, ‘76-’77, ‘82-’83, ‘91-’92, ‘97-’98, ‘02-’04, ‘06-’07, ’09’10

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Normal Conditions

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El Niño Conditions

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El Nio and Productivity

• During normal conditions, major upwelling brings nutrients and carbon dioxide into the photic zone

• Creates conditions of very high productivity (plants) and fish that feed on plants and other small fish

• El Nio shuts down the upwelling and decreases productivity

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El Niño Sea Surface Temperatures

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La Niña

• Trade winds strengthen and increase upwelling

• Unusually cold ocean temperatures in the Equatorial Pacific

• “Super normal” or opposite of El Niño

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La Niña Conditions

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La Niña—so much upwelling of cold water in eastern Pacific that it spreads to west, cooling sea surface temperatures

El Niño—large pool of warm surface water in western Pacific

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El Niño condition: departures from normal

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La Niña Impacts in U.S.

• Warmer winters in the Southeast• Cooler winters in the Northwest

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El Niño and La Niña and the Asian monsoons. When surface temperatures in the eastern equatorial Pacific are warmer than usual (an El Niño event), heavy rains hit East Africa and droughts beset India, Indonesia, and Australia. When ocean conditions flip-flop (a La Niña), so do rainfall patterns across Asia. From http://www.whoi.edu/oceanus/v2/article/images.do?id=53506

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ENSO

• El Niño/Southern Oscillation• The Southern Oscillation refers to changes

in sea level air pressure patterns in the Southern Pacific Ocean between Tahiti and Darwin, Australia.

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ENSO—note the movement of the low pressure center

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Normal

El Niño

“Southern Oscillation” (SO)

• Trade winds weaken or fail• Tropical winds reverse and go east instead

of west • Atmospheric pressure cells reverse• Wet areas become dry (drought)• Dry areas get flooded• “Oscillates” taking 3-5 months

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Southern Oscillation IndexPressure differences between Tahiti and Darwin, Australia

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Coupled Ocean-Atmosphere Circulation

Non El Niño El Niño

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Ocean’s Response to the SO

• Warm water moves to the east• Elevates sea surface temperatures (SSTs) in

SE Pacific• Shuts down upwelling, can induce

downwelling• Reduces available nutrients• Kills fish and sea birds - especially bad off

Peru23

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El Niño and Hurricanes

• Biggest influence is in North • In years with moderate to strong El Niño,

the North Atlantic basin experiences:– A substantial reduction in number of hurricanes – A 60% reduction in numbers of hurricane days – An overall reduction in system intensity

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TAO/TRITON

• Tropical Atmosphere Ocean Project (TAO)• Triangle Trans-Ocean Buoy Network

(TRITON)• Real-time data from moored ocean buoys

for improved detection, understanding and prediction of El Niño and La Niña.

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Moored Buoys

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Drifters

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Sea Surface Temperature, Winds, 20°C Isotherm, and Upper Ocean Temperature and Current at the Equator

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To view this animation and others, visit the TAO/TRITON data display page at www.pmel.noaa.gove/tao/jsdisplay/ani/html.

CTD

• Conductivity, Temperature, Depth • Detect how the conductivity and temperature of

the water column changes relative to depth. • Salinity can be derived from these two variables.• Water sampling is often done at specific depths so

scientists can learn the physical properties of the water column are at that particular place and time.

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Deploying a CTD array

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