Impacts of El Nino

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Impacts of El Nino

• Observations
• Mechanisms for remote impacts

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Observations
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Growth and Decay of El Nino
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A closer look at impacts
http//iri.columbia.edu/climate/ENSO ENSO and
CLIMATE Temperature and Precipitation Tropical
Cyclones ENSO and SOCIETY Regional
impacts http//www.pmel.noaa.gov/tao/elnino/impac
ts.html
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Mechanisms for remote impacts

• Latent heating associated with tropical
  precipitation anomalies excites waves in the
  atmosphere
• Atmospheric equatorial Kelvin and Rossby waves
  propagate zonally. Associated subsidence warms
  troposphere and suppresses precipitation
• Rossby waves can also propagate into extratropics
  (especially in winter) causing large-scale
  circulation anomalies which impact weather. (Note
  that propagation requires a westerly mean flow
  and the relevant Rossby waves have an eastward
  group velocity)

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Source D. Neelin
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Source D. Neelin
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Impacts on the North Atlantic Region
El Nino La Nina La Nina El Nino
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Impacts on marine ecosystems
Yearly average of Chlorophyll concentrations 1997
1998
El Niño low
La Niña high
Source A. Timmermann
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El Nino Prediction
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El Nino research issues

• Phase locking to seasonal cycle (onset and
  termination)
• What determines and limits the amplitude of El
  Nino?
• What controls the frequency of El Nino events?
• How will El Nino respond to anthropogenic climate
  change?