Topic 12 El Niño GEOL 2503 Introduction to Oceanography

El Ni  o A disruption of the ocean-atmosphere system in the tropical Pacific Has important consequences for weather around the globe Frequently occurs around Christmas 2

Normal conditions Strong trrade winds- 3

El Niño resources NOAA: See animations at: – ons/animations/26_NinoNina.html 4

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 5

Normal Conditions 6

El Niño Conditions 7

El Ni  o 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 Ni  o shuts down the upwelling and decreases productivity 8

El Niño Sea Surface Temperatures 9

La Niña Trade winds strengthen and increase upwelling Unusually cold ocean temperatures in the Equatorial Pacific “Super normal” or opposite of El Niño 10

La Niña Conditions 11

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 12

13 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 16

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 17

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. 18

ENSO— note the movement of the low pressure center 19 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 20

Southern Oscillation Index Pressure differences between Tahiti and Darwin, Australia 21

Coupled Ocean-Atmosphere Circulation Non El Niño El Niño 22

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 Peru 23

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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 25

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. 26

Moored Buoys 27

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Drifters 30

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Sea Surface Temperature, Winds, 20°C Isotherm, and Upper Ocean Temperature and Current at the Equator 32 To view this animation and others, visit the TAO/TRITON data display page at

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. 33

Deploying a CTD array 34