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El Nino – Southern Oscillation
- Southern Oscillation (atmosphere)
- El Nino (ocean)
- change in equatorial Pacific circulation
- produces global climate changes
- can significantly alter weather in California
Geography 104 - “Physical Geography of the World’s Oceans”
Pacific Decadal Oscillation (PDO)
variations in Pacific ocean climate on decadal scales
El Nino – Southern Oscillation (ENSO)
variations in Pacific ocean climate on few-year scales
The Southern Oscillation
• Discovered in 1928 by
Sir Gilbert Walker
• Proposes a zonal
circulation cell over
the equatorial Pacific
• Links changes to
global climate
Walker Circulation
• East-to-west pressure gradients drive
trades
Walker Circulation
• Vertical cell driven by warmest
waters
Southern Oscillation correlation coefficients are equal in magnitude, opposite in sign
atmospheric pressure: Darwin vs. Tahiti
Southern Oscillation Index
• SOI = Tahiti - Darwin air pressure ’s
• Low SOI = El Niño conditions
Southern Oscillation & warm water off S. America
Multivariate ENSO Index
• Combines observations of air pressure, zonal &
meridional components of wind, sea surface
temperature, air temperature and total cloudiness.
• Positive MEI = ENSO conditions
Pacific Ocean sea surface temperature
Western Pacific Warm Pool
normal equatorial conditions
El Nino conditions
El Niño
• Relaxation of
trade winds
causes warm
pool to slosh
esatward
across Pacific
Fig. 8.32.b
La Nina conditions
normal
El Nino
La Nina
normal
El Nino
An El Niño History• late 1800s Fishermen name El Niño to the
periodic warm waters that appear off the coasts of Peru and Ecuador around Christmas.
• 1928 Gilbert Walker describes the Southern Oscillation.
• 1957 A large El Niño is observed which affects not just the coasts of Peru and Ecuador but the entire Pacific Ocean.
• 1969 Jacob Bjerknes links the Southern Oscillation with El Niño events.
An El Niño History
• 1975 Wyrtki uses island sea level to show how eastward flow causes SST’s to rise in east Pacific.
• 1976 An idealized computer model demonstrates that winds over the far western Pacific can change SST off Peru.
• 1982 A severe El Niño develops unexpectedly, but is recorded in detail with newly developed ocean buoys.
• 1985 Several nations launch the Tropical Ocean-Global Atmosphere (TOGA) program.
An El Niño History
• 1986 First coupled model of ocean & atmosphere predicts El Niño event.
• 1988 Researchers explain how the "memory" of the ocean--the lag between a change in the winds and the response of the ocean--influences terminations of El Niño and the onset of La Niña.
• 1996-1997 The array of instruments monitoring the Pacific, plus coupled ocean-atmosphere models, enable scientists to warn the public of an impending El Niño event.
La
Niñ
aE
l N
iño
Sea surface temperature: el Niño vs normal conditions
el Niño
Dec 1996Dec 1997
la Niña
SOI
Sea surface temperature: el Niño vs normal conditions normal
el Niño
el Niño anomaly
El Niño in Australia
http://www.charterboats-uk.co.uk/Photographs/Fish/Anchovy.gif
Anchovy (Anchoa lucida - family: Engraulidae)
el Niño effects on Peruvian fishery
El Niño Temperature and Precipitation Patterns
La Niña Temperature and Precipitation Patterns
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
La Nina in the United States
El Niño in the United States
La Niña in the United States
El Niño effects on Southern California Bight
TAO-Triton mooring array
http://www.pmel.noaa.gov/tao/
TAO-Triton mooring
EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSIONissued by CLIMATE PREDICTION CENTER/NCEP/NWS 9 October 2008 Synopsis: ENSO-neutral conditions are expected to continue into early 2009. ENSO-neutral conditions continued during September 2008, as sea surface temperatures (SSTs) remained near-average in the east-central equatorial Pacific Ocean. SSTs remained slightly below-average in the central Pacific, and slightly above-average in the eastern Pacific. From west to east, the latest weekly SST index values range from −0.2°C in the Niño-4 region to +0.3°C in the Niño 1+2 region. The subsurface oceanic heat content (average temperatures in the upper 300m of the ocean, continued to decrease in response to the strengthening of negative temperature anomalies at thermocline depth in the east-central Pacific.
ENSO Summary Slide
Readings (Ocean and Atmosphere):Text Chapter 8 (pgs 138 – 163)Reader pgs. 51 - 61 Reader Maps pgs 200 - 204
Midterm on Wednesday 5 Nov 2008
