The Climate System TOPICS ENSO Impacts Seasonal Climate Forecasts III. Other modes of climate variability C. F. Ropelewski 16 November 05 Chet@iri.columbia.edu

Average conditions in the Equatorial Pacific

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

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

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

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

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

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, 1606-1626.

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

Summary of the latest ENSO Forecasts

Observed SST Anomaly, August-October 2005

Years analogous to this year through September 2005

Spring “barrier”

Historical probability 25 Historical probability

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

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

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

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

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

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

NOA index through 10 Nov 05, Source CPC/NOAA

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.