SSST = Scenario SST anomalies

The anomalous SST fields include more than one scenario for the SST anomalies predicted in at least one ocean basin. This design began in June 2004, when three possible SST scenarios were defined for the tropical Pacific SST, each representing the prediction from one of three SST prediction tools: (1) the NCEP coupled model, (2) the Lamont- Doherty Earth Observatory (LDEO) simple coupled model, and (3) the NCEP/ Climate Prediction Center's constructed analogue statistical model.

For each atmospheric model, an ensemble of runs is forced with each SST scenario.

The benefit of the multiple scenario design is that uncertainty in the SST prediction is included explicitly. Uncertainty in the future seasonal climate now includes both uncertainty in the initial climate state and uncertainty in the evolution of the bourndary forcing (i.e. SSTs).

The method of defining and using multiple SST scenarios may evolve over time.

Beginning June 2004, the following numbers of ensemble members are produced by each of the several AGCMs used in the multi-model ensemble:

                  SSST              PSST
            Scen1 Scen2 Scen3

Echam4.5       8     8     8        24

NCEP          10    10    10

Scripps        4     4     4        10

NSIPP          4     4     4

COLA          10    10    10

Internal Note

In the naming of files representing the AGCM ensemble runs, for models other than Echam4.5, 6 digits are now used instead of 5 digits. For Echam4.5, 9 digits are still used, as has been the case. When the first digit is 2, the PSST scenario is used. When it is 3, the former "ASST" scenario is used. For the new multiple scenario SST forecasts (SSST), the first digit is 4. In the case of SSST, files representing members coming from any one of the multiple SST scenarios are distinguishable: The first one-third of the ensemble members are forced by the NCEP coupled model SST prediction, the second one-third of the members by the LDEO simple coupled model SST prediction, and the third one-third by the CPC constructed analogue SST prediction.