Transcript Lecture 5: The El Nino Southern Oscillation (ENSO)

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 largescale 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
El Nino
La Nina
El Nino – La Nina
Impacts
on the
North
Atlantic
Region
Impacts on marine ecosystems
Yearly average of
Chlorophyll concentrations
El Niño
1997
low
La Niña
1998
high
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?