lesson 11: el niño southern oscillation (enso) physical oceanography
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Lesson 11: El Niño Southern Oscillation (ENSO) Physical Oceanography. We’ve learned a lot about physical forces in the oceans. What are two primary types of waves? What is one major cause of tides? What is the difference between a spring tide and a neap tide ?. - PowerPoint PPT PresentationTRANSCRIPT
Lesson 11: El Niño Southern Oscillation(ENSO)
Physical Oceanography
We’ve learned a lot about physical forces in the oceans
What are two primary types of waves?
What is one major cause of tides?
What is the difference between a spring tide and a neap tide?
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Interactions between the air and the sea are important
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1. The El Niño Southern Oscillation (ENSO) is a disruption of the ocean-atmosphere system in the Tropical Pacific, the ocean basin located between New Guinea, Australia and the Americas
2. A key characteristic of ENSO is increased surface ocean temperature in the equatorial Pacific
3. The ENSO greatly affects global weather
4. Scientists use oceanic and atmospheric data to predict ENSO events
Oceans can affect the weather
Evaporation from the ocean can transfer heat and moisture to the atmosphere and thereby affect weather patterns
Currents can also transport heat from warm areas to cool areas and vice versa Example: The Gulf Stream transfers heat from the tropics to
Europe. Without it Europe would be much colder. Upwelling, the vertical transport of cold, nutrient-rich water
from the deep water to the surface can also cool nearby areas Example: Temperatures in the Galapagos are slightly cooler than
areas at similar latitudes due to upwelling in the region. ENSO is an example of a periodic interaction between the
ocean and atmosphere that can influence global weather and climate
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How does an El Niño occur?
Photo: NOAA / OAR / PMEL
Cool, nutrient rich water (blue and green) upwells along the west coast of North and South America to replace the water being pushed toward New Guinea
Strong trade winds (white arrows) blow from the Americas toward New Guinea and Australia
Under normal conditions…..
These winds “push” water that has been warmed by the sun (red) toward the coast of New Guinea and Australia
Heavy rains are concentrated in the Western Pacific Ocean
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How does an El Niño occur?
Photo: NOAA / OAR / PMEL
Upwelling along the coast of the Americas also decreases slowing the flow of cool, nutrient rich water to the surface
Trade winds weaken
Under El Niño conditions…..
As a result of weakening trade winds, warm water (red) moves eastward along the Equator, toward the Americas(white arrows)
Ocean heat alters the jet stream, causing rains to occur beyond their normal location
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Why do we care about El Niño ?
During El Niño (and La Niña) years, more destructive weather events tend to occur:– Droughts and brush fires– Intense hurricanes– Intense tropical storms– Severe coastal flooding– Decline of some marine species (to figure out
why, think about what happens during upwelling)
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How do you think scientists can predict El Niño events?
The red color means SST is warmer, blue is cooler
SouthAmericaAustralia
During an El Nino year, SST is warmer than normal
SouthAmerica
Australia
Photo:PMEL/NOAA
By looking for abnormal sea surface temperature (SST) – known as SST anomalies
By looking at the Southern Oscillation Index (SOI)
The SOI refers to an oscillation or “seesaw” in air pressure systems between the western and eastern Pacific that is linked to El Niño
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Which graph shows a normal year and which shows an El Niño year?
A.
B.
Australia
The color code corresponds with temperature: orange and red are relativelyWarm (27-31oC) and the blues are relatively cool (20-23 oC)
South America
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Were you right?
A. Normal
Australia
The color code corresponds with temperature: orange and red are relativelyWarm (27-31oC) and the blues are relatively cool (20-23 oC)
South AmericaB. El Niño
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La Niña
La Niña causes mostly the opposite effects of El Niño– For example: In the Southeastern U.S., El Niño would typically cause
cooler winter temperatures while La Niña would typically cause warmer winter temperatures
La Niña is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific
La Niña is thought to occur due to increases in the strength of the normal patterns of trade wind circulation
These trade winds increase upwelling off the coast of South America, bringing cool water to the surface
Impacts include increased rainfall in the Western tropical Pacific
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Decide whether each graph represents normal, El Niño or La Niña conditions
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A. December 1998
B. December 1993
C. December 1997
La Niña: relatively cool SST
El Niño: relatively warm SST
Normal
Class activity
Test your skills at predicting El Niño!
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