Download - El Niño/Southern Oscillation
El Niño/Southern Oscillation
• Major climatic perturbation on the planet
• Coupled atmosphere ocean process
• Key is the western tropical Pacific
– Ascending branch of the Walker circulation
– Potential energy for Kelvin wave pulse
• www.pmel.noaa.gov/tao/elnino/nino-home.html
The Southern Oscillation
• Discovered in 1928
by Sir Gilbert Walker
• Links ’s in global
climate indices
• Proposes a zonal
circulation cell over
the equatorial Pacific
The Southern Oscillation
The Southern Oscillation
• Pressure ’s regulate strength of the trades
• El Niño periods = weak trades
Southern Oscillation Index
• SOI = Tahiti - Darwin air pressure ’s
• Low SOI = El Niño conditions
Southern Oscillation Index
Southern Oscillation
Walker Circulation
• East-to-west pressure gradients drive
trades
Walker Circulation
• Vertical cell driven by warmest
waters
Western Pacific Warm Pool
Coupled Walker/Ocean Circulation
TOGA-TAO Array
• Equatorial array of buoys (also Atlantic &
Indian)
• U.S., Japan, India, French, etc.
partnership
• http://www.pmel.noaa.gov/tao/
Moorings
• Measure met &
ocean properties
• Thermocline focus
• Real-time data
transmission
• Used in weather &
climate forecasts
TAO Moorings
TAO Moorings
Southern Oscillation
El Niño Conditions
El NiñoEvents
• Relaxation of
trades causes
warm pool to
slosh across
Pacific basin
El Niño Conditions
La Nina
• Opposite phase of the ENSO
cycle
• Intensified trades & Walker
circulation
• Thermocline undergoes
maximum upwelling
Altimetry & ENSO States
• Most “action” is in the tropical
Pacific
• Effects are seen in other
places
– East subtropics
– Western NECC region
Equatorial Kelvin Waves
• Satellite altimetry from
TOPEX/Poseidon
• Scenes are 10 days apart
Equatorial Kelvin & Rossby Waves
Off-EquatorialRossby Waves
EquatorialKelvin Waves
Planetary Waves & El Niños
Effects of an El Niño
• Region of ascending air has
moved to center of equatorial
Pacific
• Climate system shifts over
10,000 km to east
• Affects the entire planet
Effects of an El Niño
• Places that were wet are now dry and vice
versa
Effects of an El Niño
Teleconnections
• Discovered in 1928
by Sir Gilbert Walker
• Links ’s in global
climate indices
• Proposes a zonal
circulation cell over
the equatorial Pacific
El Niño & Hurricane Damage
El Niño & Diseases
El Niño
• Hadley cells intensify as source of heat is
now in central equatorial Pacific
• Jet stream intensifies & takes south path
El Niño in the United States
El Niño in the United States
El Niño in California
El Niño in California
El Niño in California
97/98 El Niño
• At its peak, the 97/98 El Niño was
biggest of all time
97/98 El Niño
97/98 El
Niño
97/98 El Niño
• TOPEX/Poseidon sea level anomaly - December 1, 1997
97/98 El Niño
OLR = outgoing longwave energy (high OLR = no clouds)
97/98 El Niño
97/98 El Niño
Present Conditions
Present Conditions
EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION
5 January 2012
Synopsis: La Niña is expected to continue into the Northern spring 2012.
Present Conditions
Nino Regions
More readings
• NOAA ENSO Page
www.pmel.noaa.gov/tao/elnino/nino-
home.html
• Review of 97/98 El Nino
www.icess.ucsb.edu/~davey/Geog158/
Readings/McPhaden_elnino_review.pdf
