El Ni

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• El Niño, climate prediction, and the
• US Southwest
• Alexandre S. Gagnon, PhD
• Department of Agronomy and Horticulture
• New Mexico State University
• Las Cruces, New Mexico
• January 18, 2004

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Outline

• Background information on El Niño, La Niña, and
  the Southern Oscillation
• The very strong 1997/1998 El Niño A case study
• Worldwide impacts of El Niño
• Climatic impacts of El Niño on the United States
  and New Mexico
• Climate prediction
• The Pacific Decadal Oscillation (PDO) and its
  role in modulating the El Niño signal
• Climate forecasts for the US Southwest
• How much confidence can we place in the
  predictions?
• Conclusions

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What are El Niño and La Niña?

• El Niño warming of the Pacific Ocean between
  South America and the Date Line, centered
  directly on the Equator, and typically extending
  several degrees of latitude to either side of the
  equator. Coastal waters near Peru also warm.
• Named by Peruvian fishermen, because of the
  appearance of warm waters off the coast of Peru
  around Christmas time
• It occurs every 2 to 7 years (irregular interval)
• La Niña essentially the opposite of El Niño,
  i.e., anomalous cooling of ocean waters in the
  eastern equatorial Pacific Ocean

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Surface temperature structure of Equatorial
Pacific showing typical La Niña, normal and El
Niño conditions. From NOAA El Niño website.
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How does El Niño work?

• Strong Trade Winds push surface waters to the
  western Pacific
• Cold, nutrient-rich water occurs at the ocean
  surface off the coast of Peru. This upwelling
  supports high biological productivity during
  normal conditions

a) Normal conditions
b) El Niño conditions

• On occasion, normal air pressure pattern
  breaks down. This
• causes Trade Winds to weaken and even
  reverse their direction,
• dragging warm and nutrient-poor water
  eastward and initializing
• El Niño conditions.

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What is the El Niño Southern Oscillation?

• This oscillation of sea surface temperatures
  (SSTs) in the tropical Pacific Ocean is
  associated with changes in the tropical Pacific
  atmospheric circulation
• The Southern Oscillation is the atmospheric
  component of the El Niño phenomenon
• Thus, the El Niño Southern Oscillation (ENSO) is
  a coupled atmosphere-ocean phenomenon. In other
  words, ENSO is an oscillation between the warm El
  Niño and the cold La Niña phases.

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The El Niño Southern Oscillation (contd)

• Not all El Niños are alike
• One index used to quantify El Niño and La Niña
  events are the sea
• surface temperatures (SSTs) in the tropical
  Pacific Ocean. Positive
• SSTs refer to El Niño conditions and negative
  anomalies refer to La
• Niña conditions in all four regions

Niño 12 (0-10S, 80-90W) Niño 3 (5N-5S,
90W-150W) Niño 4 (5N-5S, 150W-160E) Niño
3.4 (5N-5S, 120W-170W)
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SSTs in the four El Niño regions 1986-2004
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Time/longitude plot of sea surface temperatures
since 1986. From NOAA El Niño website
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Atmospheric circulation during El Niño versus
normal conditions

• Typically air rises over the western Pacific and
  sinks over the eastern Pacific.
• During an El Niño, the ocean warms by 1-2 degrees
  (0C) above its climatological average. A strong
  El Niño can result in a 3-4 degrees 0C warming
  over a large area.
• This warming affects the air pressure patterns.
  The focus of convection migrates from the
  Australian/Indonesian region eastward towards the
  central tropical Pacific Ocean
• Adverse impacts on worlds weather

Schematic representation of normal versus El Niño
conditions. From NOAA El Niño website
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The Southern Oscillation Index (SOI)

• Another index used to quantify ENSO events
• Seesaw pattern between pressure in eastern and
  western tropical Pacific
• Standardized difference in sea level pressure
  between Darwin (Australia) and Tahiti (French
  Polynesia)
• A negative SOI refers to low pressure at Tahiti
  and high pressure at Darwin, indicating El Niño
  conditions

The Southern Oscillation Index, 1950-2000
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Development of the 1997/1998 El Niño(March 1997)

• The 1997/98 El Niño is clearly the strongest
  event since 1982/83 as indicated by both the
  temperature data and the Southern Oscillation
  Index (SOI)

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Development of the 1997/1998 El Niño (contd)
(June 1997)
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Development of the 1997/1998 El Niño (contd)
(September 1997)
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Development of the 1997/1998 El Niño (contd)
(December 1997)
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Development of the 1997/1998 El Niño (contd)
(April 1998)
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History of El Niño

• El Niño is not a recent phenomenon
• coral evidence indicate El Niño's have been
  occurring for the last 2 million years
• detailed knowledge from 1500 to present
• 1525 - 1987   115 El Niño's  (Quinn Neal, 1992)

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Typical influence of El Niño

• As an El Niño develops, the first impacts are
  confined to the tropical Pacific, where Indonesia
  begins to experience drier-than-normal conditions
• El Niños shift temperature and precipitation
  patterns in many different regions of the world

From International Research Institute for
Climate Prediction (IRI)
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Typical influence of La Niña

• Impacts of La Niña
• are generally opposite
• to those of El Niño

From International Research Institute on Climate
Prediction (IRI)
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Other impacts of El Niño

• El Niño became a well known issue when the
  Peruvian anchovy
• industry collapsed after the 1972-73 El
  Niño. The warm El Niño
• waters inhibit the upwelling of colder
  nutrient rich waters thus
• limiting the food supply.
• Birds (esp. guano) population decreased due
  to lack of fish for
• food
• Hurricanes more in eastern Pacific and less
  in the
• Caribbean/Atlantic region
• Health impacts mosquito-transmitted diseases
  such as dengue
• fever and malaria

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Climatic impacts of El Niño on the United States
and New Mexico

• The impacts of El
• Niño on the US
• climate show up
• most clearly in
• the winter
• New Mexico
• typically
• experiences
• cooler winter
• temperatures
• (DJF) during El
• Niño

Maximum temperature anomalies during El Niño
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Climatic impacts of El Niño on the United States
and New Mexico (contd)

• New Mexico typically experiences wetter winters
  (DJF) during El Niño

Precipitation anomalies during El Niño in the
winter
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El Niño and New Mexico in more details

• Normal versus El Niño-average precipitation by
  climatic region
• For the southern desert, there is almost 2 times
  more winter (DJF) precipitation during a typical
  El Niño event
• Winter temperature is on average 1.3 degree
  cooler during an El Niño in the same climate
  division

Las Cruces
From NOAA-CPC website
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Overview of climatic impacts of El Niño on the US
Southwest

• With El Niño, the period October through March
  tends to be wetter than usual. Precipitation
  frequency and intensity are increased.
• El Niño winters can be 2-3 times wetter than La
  Niña winters in this region.
• Cooler temperatures during El Niño, particularly
  over New Mexico
• Large percentage of streamflow in the West is
  produced by melting of snow in the spring
• Cooler winters and a strong tendency toward wet
  winters imply a deeper snowpack in higher
  elevation and therefore greater streamflow in
  spring and summer in the Southwest during El Niño
  years.

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Climatic impacts of La Niña in the US Southwest

• Opposite of El Niño, thus dry winters during La
  Niña years
• The La Niña signal on the climate of the
  Southwest is more reliable than the El Niño
  signal. Not all El Niños bring wet winters while
  there are no exceptions to the climatic
  consequences of La Niña during the past 65 years
  in the region.
• Although El Niño has received considerably more
  attention than La Niña, the climatic consequences
  associated with La Niña winters have serious
  consequences on the New Mexican economy
• The impacts of both El Niño and La Niña are less
  clear in the summer and there are contradictory
  results from research on the relationship between
  ENSO and monsoonal rains (Sheppard et al., 2002)

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Climate prediction

• What is the difference between weather and
  climate?
• -Weather is the condition of the atmosphere at
  any particular time and place.
• -Climate is "averaged weather", the weather in
  some location averaged over some long period
  of time
• Some might wonder how we make climate predictions
  if we cant predict the weather for next week
• We cant predict the weather for next season but
  under certain conditions we can determine whether
  the next season will be warmer/cooler and
  wetter/drier than under normal climatic conditions

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Climate prediction (contd)

• What we need to know in order to forecast next
  seasons climate are variables that affect the
  atmosphere and change slowly with time such as
  the sea surface temperatures (SSTs).
• Ocean temperatures change relatively slowly and
  can be very different from one year to the next,
  especially when there is an El Niño, as explained
  earlier.
• El Niño is therefore important for long-range
  forecasting
• Other atmospheric phenomena that affect the
  year-to-year variations in the climate are the
  North Atlantic Oscillation (NAO), which shifts
  rainfall and temperature patterns over eastern
  North America and Europe, and the Pacific Decadal
  Oscillation (PDO), which, like ENSO, is more
  important for the US Southwest.

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Pacific Decadal Oscillation (PDO)

• El Niño-like pattern of Pacific climate
  variability,
• PDO "events" persist for 20-to-30 years, while
  typical ENSO
• events persist for 6 to 18 months
• Causes for the PDO are not currently known.
  Likewise, the potential
• predictability for this climate oscillation is
  not known
• Index is positive (negative) when Northeastern
  Pacific Ocean
• temperatures are warm (cool)

a) Positive warm phase
b) Negative cool phase
From NASA Jet Propulsion Laboratory
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Pacific Decadal Oscillation (contd)

• Scientists believe that we entered the 'cool'
  phase in 1998/99
• During the cool phase, the PDO causes the jet
  stream to move further north over the western
  United States resulting in decreased
  precipitation over the Southwestern states
• El Niño is stronger during positives phases of
  the PDO and La Niña is stronger during negative
  phases of the PDO

• Conversely, El Niño is weaker during negative
  phases of the PDO and La Niña is weaker during
  negative phases

Monthly values for the PDO index Jan 1900-Aug
2004. From JISAO.
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Climate prediction (contd)

• Since there is some ability to predict ENSO
  cycles, there is the possibility of making
  long-range forecasts
• NOAA successfully predicted the major El Niño of
  1997-1998 six months in advance
• Numerical models forced with current sea surface
  temperature (SST) data in the tropical ocean
  basins, and model predictions of how the oceans
  will likely evolve during the next several
  months, are used to predict mean seasonal
  patterns of temperature and rainfall
• The IRI provides a Net Assessment Forecast based
  on the
• predictions from several computer models
• (http//iri.columbia.edu/climate/forecast/net_as
  mt/
• These forecasts tell us the probability of above
  normal, normal, or below normal precipitation and
  temperature

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What are the climate forecasts for the US
Southwest?

• Climate forecast from the IRI are available for
  January - June 2005.
• These climate forecasts are based on SST data,
  notably on the weak El
• Niño conditions that currently exist and that
  are predicted to continue but
• will gradually weaken during the forecast
  period (six months for the IRI).

ENSO forecast for 2005 From IRI website
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What are the precipitation forecasts for the US
Southwest?
IRI multi-model probability forecast for
precipitation February-March-April 2005, issued
December 2004
lt- same as above but for April-May-June
2005
Enhanced probabilities for above normal
precipitation are forecast for the FMA period
over New Mexico
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What are the temperature forecasts for the US
Southwest?
IRI multi-model probability forecast for
temperature February-March-April 2005, issued
December 2004
lt- same as above but for April-May-June
2005
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Climate Predictions from NOAA-CPC
Precipitation forecast for Jan-Mar 2005 (left)
and Feb-Apr (right)

• Increased chances of above-average precipitation
  are predicted for the US Southwest for the next
  few months

Precipitation forecast for Mar-May 2005 (left)
and Apr-Jun (right)
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What was the precipitation forecast for the
strong 1997-1998 El Niño?

• There was a 55 probability that precipitation
  was going to be above average over New Mexico and
  Arizona in October-December 1997
• Was it successfully forecast?

• Validation precipitation anomalies during this
  period were 120-150 of the median value in
  southern and eastern New Mexico

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How much confidence can we place in the
predictions?

• All forecasts are fallible. In the Southwest, not
  all El Niños bring wet winters
• The climate predictions for January - June 2005
  are dependent on the accuracy of the SST
  predictions. There is some uncertainty concerning
  the evolution of SSTs small chance that El Niño
  could strengthened to moderate intensity but also
  a chance that it will weaken back to normal
  conditions
• Note that even if perfectly accurate SST
  forecasts were possible, there would still be
  uncertainty in the climate forecast due to
  chaotic internal variability of the atmosphere
• These uncertainties are reflected in the
  probabilities given in the forecast
• These climate forecasts do not fully account for
  all factors that influence regional climate
  variability and are relevant only to seasonal
  time scales and relatively large areas

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Conclusions

• Our ability to predict El Niño has led to the
  development of climate forecasts
• Weak El Niño conditions are currently observed
  and are predicted to last through winter and
  spring
• Climate models predict enhanced probabilities for
  above normal precipitation and warmer
  temperatures for winter and spring
• Will increased precipitation improved drought
  conditions?
• The PDO is currently in its negative phase and it
  may decrease the impact of El Niño over the US
  Southwest
• The PDO cycle is 20-30 years in duration will
  the PDO offset part El Niño-generated
  precipitation until 2020 (or longer)?
• Will the increased frequency of El Niño and
  decreased frequency of La Niña events benefit New
  Mexico and the US Southwest?