14 el nino other oscillations(1)
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El Nio(and other natural climate oscillations)
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1. Historical Perspective Leading to our Current Understanding
El Nio
Southern Oscillation
ENSO = El Nio Southern Oscillation
2. Direct and Indirect Impacts of El Nio on Global WeatherPatterns
3. Other types of natural climate oscillation
Outline:
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History of the Term El NioThe original definition of El Nio goes back to 18th or 19th century when Peruviansailors coined the term to describe a warm southward current that appeared annuallynear Christmas time off the Peruvian coast. Hence the name El Nio = Spanish forThe Child = "Christ Child".
The warm, southward currentoccasionally (every 3 to 7 years)seemed much more intense thanusual and eventually the term El
Nio came to refer primarily to theseoccasional extreme events
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El Nino
The Roughly Periodic (3-7 years) Occurrence of Prolonged(ca. 8 months) Warming of Coastal Waters off of Peru andEcuador
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Southern Oscillation
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In the 1920s Sir Gilbert Walker Analyzed Atmospheric Pressure DataMeasured at Darwin Australia and Tahiti and Noticed Some RemarkableCorrelations in the Two Data Sets
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Why Are The Two WeatherStations Well Correlated?
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Recall the Idealized Versus Actual Pattern of Global Sea Level PressureAnd Resulting Surface Winds
1. Differences due to unequal heating of land and ocean by the sun
2. Land heats more strongly than adjacent ocean in summer and cools more thanadjacent ocean in winter - due to differences in specific heat of rock and seawater.
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Recall the Idealized Hadley Circulation
1. Poleward-directedair aloftis deflectedto the right (northern hemisphere) --
which is toward the east2. Equatorward-directedair at surfaceis deflectedto the right(northern
hemisphere) -- which is toward thewest- to create the Trade Winds
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1. Winds at the ocean surfacemovetoward the equator,
but are deflected by Coriolistoward the (right) westtoform surface trade winds.
2. Winds aloftmove awayfrom the equator, but aredeflected by Coriolistoward
the (right) eastto completethe Walker-Circulation
Walker-Circulation
East-West Atmospheric Circulation Cell
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Coherent Change (PeriodicReversal) in the East-West Circulation CellOver the Pacific (Walker Cell) Resulting in Coherent Changes in
Atmospheric Pressure Patterns, Precipitation Patterns and Wind Direction
Southern Oscillation
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UnderNormalconditions in the Pacific the Trade Windsblow from east to west and in the process they do twothings...
1. The winds transport and pile
up warm surface water on thewestern side of the Pacific tocreate a thick (200 meters)
pool of very warm oceanwater.
2. The piled up water (warmpool) tilts the thermoclinedeeper in the west andshallower in the east.
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The Coherent Oscillation (i.e.,the Periodic Reversal)of theWalker Circulation Cell
El Nino ConditionsNormal Conditions
The Southern Oscillation
Low SLP High SLPHigh SLP High SLP
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El Nino ConditionsNormal ConditionsLa Nina Conditions
La NinaExceptionally StrongTrade Winds
Note:There is a third state to the Southern Oscillation not shown in thisfigure associated with enhanced strength in the Trade Winds
NormalTrade Winds
ReversedTrade Winds
Exceptionally StrongTrade Winds
The Coherent Oscillation (i.e.,the Periodic Reversal)of the WalkerCirculation Cell
The Southern Oscillation
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Southern OscillationIndex(SOI):1. A simple index (i.e., a single number) used to describe the severity of
El Nino conditions - i.e., the strength of the reversal in the Walker
Circulation
2. Traditionally defined as the normalized difference in atmospheric
pressure measured at Darwin Australia and Tahiti, but moreelaborate and robust metrics also exist.
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Southern Oscillation Index
Red = El Nino ConditionsBlue = La Nina Conditions
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El Nino Southern Oscillation (ENSO)
Coupled Ocean-Atmospheric Interactions
1. Roughly periodic (3-7 years) occurrence of prolonged (ca. 8 months) warming
of coastal waters off of Peru and Ecuador
2. Coherent change in the east-west atmospheric circulation cell over the Pacific
(Walker Cell) resulting in coherent changes in atmospheric pressure patterns,
precipitation patterns and wind direction
3. And Much Much More
In 1969Jacob Bjerknes proposed that there was a physical connection between the
oceanographic and atmospheric variations and now the oceanic (El Nino) and the
atmospheric (Southern Oscillation) aspects are combined in the single term 'El
Nio Southern Oscillation' (ENSO) that encompasses both the ocean and theatmosphere
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La NinaExceptionally Strong Trade
Winds, Equatorial Upwelling andCooling in the Eastern Pacific
El Nino
Exceptionally Weak or ReversedTrade Winds, Little or NoEquatorial Upwelling and Strong
Warming in the Eastern Pacific
NormalNormal Trade Winds, Upwellingand Cooling in the Eastern Pacific
Sea Surface Temperature Patterns During La Nina, El Nino and
Normal Conditions in the Pacific
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Warming of the surface water off of Peru during an El Nino Event is part of a
much greater warming event covering large parts of the eastern tropical Pacificand reaching down to the thermocline
El Nino ConditionsNormal Conditions
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Temperature Field in the Pacific Prior to El Nino(Normal Conditions)
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Temperature Field in the Pacific During the InitialProgression of El Nino
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Temperature Field in the Pacific During the Recoveryfrom El Nino
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El Ninos Progression March:Westerly Wind Burst
north of Australia
April:Kelvin Wave ReachesSouth America
May:Water Piles up off of SouthAmerica
June:High Sea-Level SpreadsNorth and South
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QuestionWhat should happen to global-averagetemperature when the thick warm pool of waterin the western Pacific spreads out across a largearea of the equatorial Pacific during an El Nino
period?
a) Global Temperature Should: Go Up
b) Global Temperature Should: Go Down
c) Global Temperature Should: Stay About the Same
The Correct Answer is (a) temperatures willgo upas thearea of warm water in contact with the atmosphere increasesand allows the ocean to give up some of its stored heat to theatmosphere
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Global Temperature Anomalies Since the Industrial Era
1880 1900 1920 1940 1960 1980 2000!
.4
!.2
0.
.2
.4
.6
12-month Running Mean (C)
Land!Ocean Temperature Index
Temperatures are Relative to Base Period 1950-1980
1997-1998El Nino
1999-2000
La Nina
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Environmental Change LinkedDirectly and Indirectly to El Nio
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1. Relative Cooling in the Western Tropical Pacific Creates Drought Conditionsin Australia/IndonesiaDuring an El Nino
2. Relative Warming in the Central and Eastern Tropical Pacific Heat Energy forFormation of Intense Precipitation and Storms
El Ninos DirectImpact on Pacific Precipitation and
Storm Patterns
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Draught and Fires in Indonesia
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Pacific Hurricanes Increase During an
El Nino, but Atlantic Hurricanes Decrease
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Flooding in the Western United States
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El Ninos DirectEffect on Equatorial Productivity
El Nino ConditionsNormal ConditionsHigh Equatorial Productivity Low Equatorial Productivity
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El Nios DirectEffect on Biological Productivity off of
Peru and Ecuador
NormalConditions
El NioConditions
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Environmental Changes Linked Indirectlyto El NioTeleconnections
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El Nino Related Changes in Global Climate
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The answer to how El Nino can influence weather patterns around to
globe lies in what El Nino can do the the Jet Streams that circle the globe
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Changes in the Jet Stream During El Nino and La Nina
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Prevailing Wind Direction at a Given Location is Strongly Influenced by the
Position of the Jet Stream
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Jet streams have wave-like properties and just like a disturbance in water causes a wave to
propagate outward, so too does a regional disturbance in the jet stream position propagate inwave-like fashion around the globe. ENSO produces such a disturbance that can thenpropagate around the world.
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More Info About El Ninohttp://www.pmel.noaa.gov/tao/elnino/nino-home.html
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Other Natural Climate Variations
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Other Natural Climate Variations
1. El Nino Southern Oscillation (ENSO)
2. North Atlantic Oscillation (NAO)
3. Atlantic Multi-Decadal Oscillation (AMO)
4. Pacific Decadal Oscillation (PDO)
5. Arctic Oscillation (AO)
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Positive NAOStrong pressure difference betweenIceland and Azores
Stronger Westerly Winds LocatedMore Northward
Negative NAOWeak pressure difference betweenIceland and Azores
Weaker Westerly WindsLocated More Southward
North Atlantic Oscillation (NAO)
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North Atlantic Oscillation Index
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Pacific Decadal Oscillation (PDO)
Positive Phase:
North Pacific cooler than normal
Equatorial Pacific warmer thannormal
Negative Phase:North Pacific warmer than normal
Equatorial Pacific cooler than normal
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Pacific Decadal Oscillation (PDO) Index
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Atlantic Multi-Decadal Oscillation
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Atlantic Multi-Decadal Oscillation Derived fromGlobal SST Data
Time Variation of AMO
similar colors rise and fall in unison fromyear to year or decade to decade.
purple and red colors are out of phase - yearsor decades of high temperatures for redmeans low temperatures for purple regionsfor the same year or decade
Spatial Coherence of AMO
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Atlantic Multi-Decadal (AMO)Index Derived by Removing the
Multi-Decadal Global SST Linear Trend
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The Atlantic Multi-Decadal Oscillation Causes Warming and Cooling of
Sea Surface Temperatures that, in turn, Cause Increases and Decreases inAtlantic Hurricanes
Hurricane Tracks1985-1994
Hurricane Tracks1995-2004
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Atlantic Multi-Decadal (AMO)Derived by Keeping the Multi-Decadal Global SST Linear Trend
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With the multi-decadal trend included it becomes more doubtful that
hurricane activity will ever decline in subsequent decades
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Summary
1. Besides El Nino Southern Oscillation (ENSO) there are a large number of
other natural climate oscillations that change phase (sea surface temperaturepattern and wind velocity pattern) on the order of decades
2. When examining the issue of global warming, one needs to take into accountnatural climate variability that can occur on the order of decades!
3. Global Warming is a Multi-Decadal Trend with natural decadal
oscillations superimposed on that trend!
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Global Temperature Anomalies Since the Industrial Era
1880 1900 1920 1940 1960 1980 2000!
.4
!.2
0.
.2
.4
.6
12-month Running Mean (C)
Land!Ocean Temperature Index
Temperatures are Relative to Base Period 1950-1980
1997-1998El Nino
1999-2000La Nina
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