Objectives
 learn
how El Niño and La
Niña work
 emphasize that the ocean
& atmosphere are
strongly coupled
 understand that one
component of the Earth’s
system can have drastic
effects on the rest of the
Earth
El Niño: The Enigma
Unusual
oceanic and atmospheric
phenomenon - an anomaly
–We don’t know everything about it
–We can’t really predict it yet
El Niño: The Term
First
discovered in 1795
Recognized by local fisherman along
Ecuador and Peru
–Warm, surface countercurrent
–North-->South
–Discovered around Christmas-time
–“The Christ Child”
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
Slides from 1982-’83 El Niño
INDEX =
• Air temperature
• Sea surface temp
• Surface winds
• Cloudiness of sky
• Sea level pressure
-09-’10
Elevated
Sea Surface
Suppressed
Sea Surface
“Southern Oscillation” (SO)
Tradewinds
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”
like a giant sea-saw,
taking 3-5 months
Non El Niño
El Niño
Coupled Ocean-Atmosphere
Circulation
Non El Niño
El Niño
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
Animations
Ocean AND Atmosphere
El
Niño is both an oceanic and an
atmospheric phenomenon
–Often called ENSO
Scientists
knew of SO from wind and
precip. data
Scientists knew of El Niño from SST
data
Didn’t make connection until 1969
Jacob Bjerknes
Jacob
Bjerknes, a Norwegian
meteorologist made breakthrough in
1969
Combined wind, rain, AND SST data
Ocean & atm. part of “big climate
engine”
Effects of ENSO not just local to Peru
but could affect whole Pacific, whole
world
Interdisciplinarity Rules!
Bjerknes
was a meterologist who
was willing to take a good, hard look
at oceanographic data
Oceanography a versatile science
How Do We Track El Niño Today?
in
situ (on site) measurements
Satellite sea surface temperature
Computer models
Autonomous Temperature Line Acquisition System
Tropical Ocn Global Atm
Tropical Atm-Ocn
La Niña
 NOT
tied to the Southern Oscillation
 Tradewinds get stronger
 SSTs are lowered in SE Pacific
 Normal conditions are exaggerated
– Dry areas get drier (drought)
– Wet areas get wetter (floods)
 Occurs
in between El Niños
INDEX =
• Air temperature
• Sea surface temp
• Surface winds
• Cloudiness of sky
• Sea level pressure
El Niño AND La Niña
Both
an ocean/atmosphere
phenomenon
Both affect wind, rain, and SST
Both occur in cycles
More Animations
El Niño VERSUS La Niña
 “Southern
Oscillation”
 Tradewinds fail
 Reverse flow of air
 Elevated SST
 Upwelling decreased
 Fish die
 Dry areas flood
 Wet areas dry up
 No
oscillation
 Tradewinds increase
 No reverse flow
 Decreased SST
 Upwelling increased
 Fish thrive
 Dry areas get drier
 Wet areas flood
Lesson to be Learned
 Earth
phenomena are very much
interrelated
Ocean <----> Atmosphere
 Bjerknes’
concept of “teleconnections”
 We must understand in order to predict
 Invest in soybean futures after an El Niño!
– No fish meal for cattle, farmers will use soy
We’re dealing with the interplay between two
very different fluids - atmosphere and ocean - in
the boundless dimensions of time and space. ...
Abnormality in one causes abnormality in the
other.... 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, Scripps
Institution of Oceanography