1. The Climate System TOPICS ENSO Impacts Seasonal Climate Forecasts
III. Other modes of climate variability
C. F. Ropelewski
16 November 05

2. Average conditions in the Equatorial Pacific

3. El Niño Trade winds get weaker Warm water flows back eastward
Convection moves eastward
Winds weaken further…

4. Evolution of the 2002 El Niño, Jan 2002 to Jan 2003
Start
NINO3.4
Time Series
Stop

5. Correlation between Darwin sea level pressure (SLP) and slp everywhere.

6. All El Niño
and
La Niña
episodes are unique,
but they share
common features

7. El Niño Events tend to peak near end of the year
There is some tendency for La Niña events to follow.

8. El Niño, after Ropelewski and Halpert 1987, MWR, 1606-1626.
Regions with consistent precipitation anomalies associated with
El Niño, after Ropelewski and Halpert 1987, MWR,

9. Dec - Feb
Jun-Aug a) b)
Time series of seasonal rainfall anomalies a) for December to
February, b) June to August. The colors represent the sea surface
anomaly in the central equatorial Pacific (red for El Niño,
blue for La Niña). The mean annual cycle of precipitation is
shown by the graph to the left.
ENSO impacts at a location in the Florida panhandle. For other locations
Go to iri.columbia.edu/climate/ENSO/globalimpact/
Click on Global Effects of ENSO

11. Summary of the latest ENSO Forecasts

12. Observed SST Anomaly, August-October 2005

13. Years analogous to this year through September 2005

14. Spring “barrier”

15. Historical probability25
Historical probability

17. Numerical Model-based
Seasonal Climate Forecasts
2-tier forecasts (Assumes that the ocean
boundary provides the “memory” for seasonal
prediction)
Forecast the Sea Surface Temperature
Drive Atmospheric Models with the
Predicted SST
iii. Combine the outputs from several models

18. IRI DYNAMICAL CLIMATE FORECAST SYSTEM
2-tiered
OCEAN ATMOSPHERE
GLOBAL
ATMOSPHERIC
MODELS
ECPC(Scripps)
ECHAM4.5(MPI)
CCM3.6(NCAR)
NCEP(MRF9)
NSIPP(NASA)
COLA2
GFDL
PERSISTED
GLOBAL
SST
ANOMALY
Persisted
SST
Ensembles
3 Mo. lead 10
POST
PROCESSING
MULTIMODEL
ENSEMBLING 24 24
FORECAST SST
TROP. PACIFIC: THREE
(multi-models, dynamical
and statistical)
TROP. ATL, INDIAN
(ONE statistical)
EXTRATROPICAL
(damped persistence) 12
Forecast
SST
Ensembles
3/6 Mo. lead 24 24 30 12 30 30

25. What do we know about shorter term climate variability? Seasonal Modes
El Niño/Southern Oscillation (ENSO) including
La Niña
(North) Atlantic Oscillation (N)AO
Decadal Modes (?)
Atlantic
Pacific Decadal

28. Monthly (3MRM) NAO Index though September 05, Source, CPC/NOAA

29. Index of Observed Rainfall for the August to October season 2005.

30. Black – 5 MRM
Blue – JFM only
Seasonal Mean NAO, Source CPC/NOAA

31. NOA index through 10 Nov 05, Source CPC/NOAA

34. Summary
No two El Nino Episodes are exactly alike
Nonetheless, consistent broad patterns of rainfall
(and temperature) tend to occur in association
with ENSO
The primary lesson from studying ENSO is that
the surface Boundary conditions (especially the
Equatorial Pacific SSTs) provide the “memory”
for seasonal Prediction.
The 2005 winter season is likely to proceed without
the benefit of strong boundary forcing and thus be
less predictable than in ENSO years.