OC/GEO 103 - El Nino

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El Niño and La Niña
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Objectives of Lecture:

to gain a simple understanding of how the El Niño phenomenon works
to emphasize that the ocean and atmosphere processes are closely linked to one another
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.

normally develops in the western tropical Pacific
often results in natural disasters
occurs every 2 to 10 years
First discovered in 1795
Most recent and severe El Niños were in: 1953, '57-'58, '65, '72-'73, '76-'77, '82-'83, '87-'88, and '97-'98, '02-'03
implies El Niño occurs in cycles

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"

tradewinds weaken or fail
tropical winds reverse and go east
atm. pressure cells reverse
- wet areas become dry (drought)
- dry areas get flooded

Ocean's Response

warm water moves to the east
elevates SST in SE Pacific
shuts down upwelling, can induce downwelling
reduces available nutrients
kills fish and sea birds -- very bad for fishing industry off Peru

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.

Bjerknes:

used the most up-to-date wind, rain, and SST data to show that the Southern Oscillation and El Niño were NOT separate phenomena - sometimes abbreviated ENSO
ocean and atmosphere were part of one big "climate engine"
effects of El Niño not just local to Peru but could affect whole Pacific and even the whole world

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")

NOT tied to the Southern Oscillation
tradewinds get stronger
SST's are lowered in the SE Pacific
normal conditions are exaggerated
- dry areas get drier (drought)
- wet areas get wetter (floods)
occur in between El Niños - 1955, '63-'64, '66, '70, '75, '88, '98

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:

Earth phenomena are very much interrelated
Ocean <======> Atmosphere
A significant change in any one component of the Earth's system may have drastic effects on the rest of the Earth (Bjerknes' concept of "teleconnections")
We must understand El Niño in order to predict its coming and thus be better prepared to avert disaster
Invest in soybean futures the year after an El Niño!
Because El Niño years are bad for the fishing industry, there will be no fish to eat for humans and no fish meal to be used to feed cattle. Unhappy cattlemen will then turn to soybeans as an alternative to feed their cattle.

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