1. Impacts of El Nino
Observations
Mechanisms for remote impacts

2. Observations
What are the impacts?

3. Growth and Decay of El Nino

4. Fig. 4.

7. A closer look at impacts
ENSO and CLIMATE
Temperature and Precipitation
Tropical Cyclones
ENSO and SOCIETY
Regional impacts

8. Mechanisms for Remote Impacts How do these impacts occur?

9. 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)

10. Source: D. Neelin

11. Stationary wave number Ks=sqrt(beta/u); k is set by forcing
Source: D. Neelin

12. Impacts on the North Atlantic Region
El Nino – La Nina La Nina El Nino

13. 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?

14. El Nino Prediction (next lecture)