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El Niño and La Niña
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Objectives of Lecture:

  1. to gain a simple understanding of how the El Niño phenomenon works
  2. to emphasize that the ocean and atmosphere processes are closely linked to one another
  3. to understand that one component of the Earth's system can have drastic effects on the rest of the Earth
El Niño = unusual climate and oceanic phenomenon that we still don't know everything about, nor can we really predict it

"The Christ Child" = first recognized as a warm surface countercurrent flowing down the coasts of Ecuador and Peru around Christmastime, so that's what the local fisherman called it.

Images below courtesy of Diane Schweizer, Institute for Computational Earth System Science, UCSB

Best way to understand how El Niño occurs is to look at what happens in the Pacific under normal circumstances and then we'll see how things are literally reversed during an El Niño event.

Normal vs. El Niño Conditions

Sometime in the fall or winter an event known as the "Southern Oscillation" may occur

"Southern Oscillation"

Ocean's Response

Whole process takes 3 to 15 months, after which whole thing returns to normal, which is why southern oscillation is called an "oscillation" - like a giant see-saw

Jacob Bjerknes

It's very important to remember that El Niño is both an oceanic and an atmospheric phenomenon

The ocean and atmosphere are very closely linked and the first person to realize this and to convince the scientific community of it was a Norwegian meteorologist named Jacob Bjerknes His ideas made a big impact in 1969 when he wrote what is known as the Bjerknes Hypothesis

People knew that the Southern Oscillation existed from wind and precipitation data in the Pacific and they knew about El Niño because of the anomalously high SST's near Peru but they didn't realize the 2 were part of the same phenomenon.


This was borne out by the '82-'83 El Niño where only Antarctica and Europe were not affected in some way

Bjerknes also showed that it's good to be interdisciplinary - he was a meteorologist but he was versatile enough to take a good hard look at oceanographic data. Also, oceanography is inherently an interdisciplinary science, which makes it quite versatile

How We Track El Niño Today

in situ (on site) measurements such sea surface temperature, sea surface height, wind speed and direction, current direction, current velocity, size and abundance of fisheries

sophisticated moorings with several instruments that can make these measurements

Many of these instruments part of the TAO (Tropical Atmosphere Ocean) Array

TAO is part of the TOGA (Tropical Ocean Global Atmosphere) COARE (Coupled Ocean-Atmosphere Response Experiment) Program, started in 1985

satellite measurements, particularly of sea surface temperature

combinations of various kinds of data

that can be put into predictive models

La Niña

Another phenomenon related to El Niño is called La Niña ("the girl")

El Niño AND La Niña

Both an ocean/atmosphere phenomena

Both affect wind, rain, and SST patterns

Both appear to occur in cycles

El Niño VERSUS La Niña

El Niño La Niña
"Southern Oscillation" No "oscillation"
Tradewinds fail Tradewinds increase
Reverse flow of air No reverse flow
Elevated SST Decreased SST
Upwelling decreased Upwelling increased
Fish die Fish thrive (can still be a
bad deal if fish prices drop)
Dry areas flooded Dry areas get drier (e.g., Florida)
Wet areas dry up Wet areas get flooded (e.g., Oregon)

Lessons to be learned from El Niño:

Closing Quote

"We're dealing with the interplay between two very different fluids -- atmosphere and ocean -- in the boundless dimensions of time and space. Neither medium has a 'normal' state, and abnormality in one causes abnormality in the other. Weather is always abnormal. Events such as El Niños have no definite starting point and no end -- it's a matter of where you break into the scene, and where you leave it. Perhaps the only thing more complex is human behavior itself."
-- Dr. Jerome Namias, forecast specialist, Scripps Institution of Oceanography

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