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Date: 21-Jul-15
AS Unit 1 Topic 1
El Niño/La NiñaShort term climatic change
Date: 21-Jul-15
AS Unit 1 Topic 1
El Nino/La Nina:
A WELCOME or UNWELCOME VISITOR?
• P 24-25 Pearson
• P 19-20 Philip Allan
• 2 x Geofiles (on the blog)
http://www.pbs.org/wgbh/nova/elnino/
http://oceanworld.tamu.edu/
http://www.bbc.co.uk/weather/features/el_nino_events.shtml
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• El Nino and La Nina are amongst the most
powerful phenomena on the earth as they
affect the climate over almost half of the
earth.
• El Nino (means male child in Spanish) and it
refers to a weak warm current appearing
around Christmas along the coast of Ecuador
and Peru. They happen every 3-4 years and
may last from 12-18 months.
• Over the last few decades there have been
more stronger events and the term El Nino is
now linked more closely to these.
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• La Nina (meaning female child in Spanish)
refers to an anomaly of cold sea surface
temperatures found in the eastern tropical
Pacific (by Australia and Indonesia etc)
• La Nina episodes may follow El Nino (but not
always.
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What is happening usually?
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Hadley Cells
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•
Normal years
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• Under normal conditions there is high air
pressure off the coast of Peru and Ecuador
with descending air resulting in the Atacama
desert
• And there is low air pressure over the
western Pacific (Australia and Indonesia)
giving heavy convectional rainfall.
• This movement of air results in the Walker
cell.
• The upper air moved west to east and the
lower air moves from east to west as the
trade winds.
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• Surface water gets pushed westwards …. The
sea level is normally 60cm higher in the
Philippines than in Panama/Colombia
• Water flowing westwards stays warm (28
degrees C in the western Pacific).
• Cold water(20 degrees C) that wells up near
Peru and Ecuador is rich in plankton and
great for fishing.
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And in El Nino years?
• These are scientifically called an El Nino
Southern Oscillation (ENSO) and happen
every 3-4 years and may last from 12-18
months.
• There is a reversal to normal conditions.
• Pressure rises over the Western Pacific
(Indonesia and Australia) and falls over
the Eastern Pacific (Peru and Ecuador)
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• The Inter Tropical Convergence Zone (ITCZ) shifts
South and causes trade winds to weaken and
maybe even reverse their direction.
• Air descends over South East Asia (drier weather)
and ascends over the west coast of South America
(wetter weather).
• The changing trade winds means that sea level in
South East Asia tends to fall and it rises in tropical
South America.
• Surface temperatures to the East is warmer and
there is less upwelling of cold water off Peru. Sea
temperatures there may rise by 6 degrees C so
plankton suffers as does Peru’s fishing industry.
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Normal Year
El Nino
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Sea Level
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El Niño Builds, Warm Wave Surges Toward South America
November 20, 2006
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• Examples of El Nino – 1982-83, 1986, 199293, 1997-98
• Effects of El Nino
•
Change of weather around the world
•
The very strong El Niño of 1997-98 caused:
•
South America
•
High evaporation and precipitation – For each of 12 days in early March Peru got 6 months
of normal rain. Flash floods killed 292, injured more than 16,000, destroyed 13200 homes
and wrecked roads and farmland. Half a million Peruvians affected.
•
Economic disaster to the Peruvian fisheries.
•
Some plants blooms for the first time in 100 years in the Atacama desert
•
Indonesia and Australia
•
Droughts in Australia, which caused a water shortage.
•
Lake Eyre in Australia dried up
•
Indonesian forest fires caused severe haze over several countries
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Effects of El Nino in other parts
of the world
•
Other parts of the world
•
severe coastal storms, heavy rainfall, flooding and mud slides in California on the
west coast of the United States.
•
droughts in Mexico and Central America, which led to forest fires that burned for long
periods of time and sent heavy smoke north to the United States
•
unusually mild winters on the east coast of the United States – very little snow in the
Rockies
•
Heavy rain increases wildlife in Botswana
•
Late arrival of monsoon in Indian subcontinent
•
Droughts in SE Asia
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Sydney Dust Storms Sept 2009
http://www.dailytelegraph.com.au/news/gallery/gallery-e6frewxi1225778417848?page=7
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La Nina
• The ‘little girl’ is the reverse of El Nino.
• It has occurred less frequently than El
Nino.
• It is less easy to predict due to less
evidence.
• The low pressure over the Western Pacific
(Indonesia and Australia) becomes even
lower and the high pressure over the
Eastern Pacific (Peru and Ecuador) even
higher.
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• Rainfall increases over South East Asia
• And drought conditions happen in South
America.
• The increased difference in air pressure over
the Pacific strengthens trade winds.
• Larger amounts of water are sent westwards
giving higher sea levels in Indonesia
• There is an even greater upwelling of cold
currents on the Peruvian coast
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One of the strongest La Niñas blankets the Pacific Ocean near the equator,
This La Niña is indicated by the blue area in the centre of the image along the equator. Blue
indicates lower than normal sea level (cold water). The data were gathered in early April 2008
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Effects of La Nina
• Scientists believe that la Nina could be
linked to greater hurricane activity in the
Caribbean.
• It also interrupts the jet stream by the mid
latitudes, like the UK, giving stormier,
wetter and cooler conditions.
• See the diagram on the next page.
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So what do you think: A WELCOME or UNWELCOME VISITOR ?
• Essay
How does El Nino and La Nina affect
weather patterns? (10 marks)