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Impacts of El Nino
• Observations
• Mechanisms for remote impacts
Observations
Growth and Decay of El Nino
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/impacts.html
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)
Source: D. Neelin
Source: D. Neelin
Impacts on the North
Atlantic Region
El N
ino
– L
a N
ina
L
a N
ina
E
l Nin
o
Yearly average ofChlorophyll concentrations
1997
1998
El Niño
low
La Niña
high
Impacts on marine ecosystems
Source: A. Timmermann
El Nino Prediction
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?
