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