El NioSouthern Oscillation

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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

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The Southern Oscillation

• Discovered in 1928 by Sir Gilbert Walker
• Links Ds in global climate indices
• Proposes a zonal circulation cell over the
  equatorial Pacific

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The Southern Oscillation
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The Southern Oscillation

• Pressure Ds regulate strength of the trades
• El Niño periods weak trades

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Southern Oscillation Index

• SOI Tahiti - Darwin air pressure Ds
• Low SOI El Niño conditions

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Southern Oscillation
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Nino Regions
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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

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Walker Circulation

• East-to-west pressure gradients drive trades

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Walker Circulation

• Vertical cell driven by warmest waters

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Western Pacific Warm Pool
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Coupled Walker/Ocean Circulation
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Coupled Walker/Ocean Circulation
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El NiñoEvents

• Relaxation of trades causes warm pool to slosh
  across Pacific basin

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El Niño Conditions
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El Niño Conditions
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La Nina

• Opposite phase of the ENSO cycle
• Intensified trades Walker circulation
• Thermocline undergoes maximum upwelling

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Today
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Today
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Altimetry ENSO States

• Most action is in the tropical Pacific
• Effects are seen in other places
• East subtropics
• Western NECC region

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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

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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.

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An El Niño History

• 1975 Wyrtki uses island sea level to show how
  eastward flow causes SSTs 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.

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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.

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Coupled Walker/Ocean Circulation
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El Niño Conditions
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Effects of an El Niño

• Places that were wet are now dry and vice versa

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Effects of an El Niño
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El Niño in Australia
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El Niño in Australia
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Teleconnections

• Discovered in 1928 by Sir Gilbert Walker
• Links Ds in global climate indices
• Proposes a zonal circulation cell over the
  equatorial Pacific

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El Niño

• Hadley cells intensify as source of heat is now
  in central equatorial Pacific
• Jet stream intensifies takes south path

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El Niño in the United States
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El Niño in the United States
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El Niño in the United States
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El Niño in the United States
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El Niño Hurricane Damage
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El Niño Hurricane Damage
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El Niño Diseases
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Delayed Oscillator Theory

• Seeds of El Nino destruction as it starts...

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Delayed Oscillator Theory
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Delayed Oscillator Theory
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El Niño Conditions
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97-98 El Niño Event
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97/98 El Niño

• At its peak, the 97/98 El Niño was biggest of all
  time

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97/98 El Niño
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97/98 El Niño
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97/98 El Niño

• TOPEX/Poseidon sea level anomaly - December 1,
  1997

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97/98 El Niño
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97/98 El Niño

• OLR outgoing longwave energy (high OLR no
  clouds)

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97/98 El Niño
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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/Geog163/950.pdf