El Nio Southern Oscillation ENSO

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El Niño / Southern Oscillation(ENSO)

• By Sagar Bora
• University of Bremen

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Outline

• Motivation/History
• El Niño/La Niña definition
• Normal Conditions in the Pacific Ocean
• El Niño Conditions
• La-Niña Conditions
• Effects of El Niño and La-Niña
• El Niño facts
• Summary

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El Niño

• From the mid 18th century, Peruvian fisherman
  noticed that their harvest completely failed
  every few years.
• This periodic event was associated with unusually
  warm waters off the coast of Peru.
• Since the periodic warming almost always occurred
  around December, the fisherman named it El Niño,
  in reference to the Christ child.

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Southern Oscillation

• In the late 19th century Gilbert Walker, the head
  of the Indian Meteorological Service notices that
  the Indian monsoon fails periodically every few
  years, leading to drought and famine in India.
• Search for a way to predict the Indian monsoon.
• Identified a peculiar see-saw relationship
  between pressure over the maritime continent and
  India and the Pacific near South America.
• He called this relationship the Southern
  Oscillation.

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ENSO

• In 1969, UCLA professor Jacob Bjerknes was
  the first to recognize that El Niño and the
  Southern Oscillation are actually manifestations
  of the same physical phenomenon and that it
  results from an unstable interaction between the
  atmosphere and the ocean. This resulted in the
  term ENSO to refer to this phenomenon.

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Why should we study El Niño?

• Reduced upwelling off the coast of South America.
  So periodic failure of fishery near Peru, which
  normally is responsible for one-fifth of global
  fish production. High coral mortality
• Drought in South-east Asia, India, Australia and
  Africa
• Heavy rainfall in the South Americas

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El Niño definition

• From
  www.weathersa.co.za
• El Niño When the three-month running mean of
  the Sea Surface Temperature anomalies in the Nino
  3.4 region are greater than or equal to 0.5C, an
  El Niño event is assumed to be taking place.

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La Niña definition

• From www.weathersa.co.za
• La Niña When the three-month running mean of
  the Sea Surface Temperature anomalies in the Nino
  3.4 region are greater than or equal to -0.5C,
  an La Nina event is assumed to be taking place.

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Normal Conditions in the Pacific Ocean

• Nutrient rich cool water along the Peruvian coast
  (eastern pacific) due to upwelling
• good for marine life
• Shallow mixed layer thermocline raised
• 3 to 8 C warmer water in the west Pacific near
  Australia, Indonesia
• Deep mixed layer thermocline pushed down

From www.weathersa.co.za
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Normal Conditions in the Pacific Ocean
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
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Normal Conditions in the atmosphere

• High pressure in the east above the cold water,
  low pressure in the west above the warmer water
• Pressure gradients result in easterly trade winds
  which in turn results in upwelling along the
  Peruvian coast
• Trade winds brings moist warm air towards
  Indonesian region which rises and travels
  eastward before sinking in the east. This is a
  thermally direct circulation found by Sir G.
  Walker.

From www.weathersa.co.za
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El Niño Conditions in the atmosphere

• Easterly winds weakens, even changes directions
  sometimes and becomes westerlies due to change in
  the sign of pressure gradient. Sir Walker called
  this east-west seesaw in southern Pacific
  pressure Southern Oscillation

From www.weathersa.co.za
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El Niño conditions in the Pacific Ocean

• Due to change in the wind direction, the currents
  on the ocean also slows down or changes direction
  from westward to eastward.
• SST rises in the eastern pacific and the western
  pacific cools down a bit Downwelling occurs off
  the coast of Peru nutrient-less warm surface
  water leads to decline in marine life
• Rainy conditions move with the warmer SST and dry
  conditions move with the cold

From www.weathersa.co.za
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El Niño Conditions in the Pacific Ocean
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
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A normal year and an El Niño year
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
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La Niña conditions

• During La Niña years, the upwelling off the
  Peruvian coast is enhanced and the SSTs in the
  Nino regions become cooler than usual.
• The Walker Circulation operates in the same way
  as described for normal years, but because of the
  larger area of colder water off the South
  American coast and the displacement of warmer
  water to the west, the atmospheric pattern also
  shifts accordingly. Heavier rainfall over
  Australia and Indonesia and dry spans over South
  Americas

From http//www.wrh.noaa.gov/
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La Niña conditions in the Pacific Ocean
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
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Global impacts of El Niño
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
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Global impacts of La Niña
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
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El Niño facts

• ENSO is not a weather anomaly, its a part of a
  cycle.
• Every weather anomaly throughout the world that
  occurs during an El Niño year is not caused by
  that El Niño.
• The impact of global warming on El Niño is not as
  yet known, speculation notwithstanding.
• Forecasting El Niños onset does not tell us much
  about its other characteristics (e.g., intensity,
  frequency, duration).

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Summary and conclusions

• El Niño , La Nina and the Southern Oscillations
  are coupled phenomenon that occurs periodically
  at the Pacific Ocean.
• Normally, SST and SSH at the eastern pacific is
  lower than the western pacific.
• During El Niño , its the opposite of the normal
  conditions. SST and SSH rises in the eastern
  pacific and easterlies slows down or changes
  direction.
• La Niña is the extreme of the normal conditions.
  SST at the east coast decreases more than usual.
• Both La Niña and El Niño effects the global
  climate and the economy of many countries.

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Thank you for Listening!!Questions?