Title: El Nio Southern Oscillation ENSO
1El Niño / Southern Oscillation(ENSO)
- By Sagar Bora
- University of Bremen
2Outline
- 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
3El 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.
4Southern 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.
5ENSO
- 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.
6Why 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
7El 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.
8La 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.
9Normal 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
10Normal Conditions in the Pacific Ocean
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
11Normal 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
12El 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
13El 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
14El Niño Conditions in the Pacific Ocean
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
15A normal year and an El Niño year
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
16La 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/
17La Niña conditions in the Pacific Ocean
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
18Global impacts of El Niño
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
19Global impacts of La Niña
Source http//www.wrh.noaa.gov/fgz/science/elnino
.php?wfofgz
20El 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).
21Summary 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.
22Thank you for Listening!!Questions?