This “model-analog” technique is applied to half (four) of the CGCMs comprising the North American Multimodel Ensemble (NMME): NCAR-CCSM4, NCAR-CESM1, GFDL CM2.1, and GFDL CM2.5 (FLOR). The length of the corresponding control model runs ranges from 700-4200 years, allowing a test of the sensitivity of the technique to both data availability and ensemble size. Model-analogs are determined only over the tropical IndoPacific domain, using monthly SST and SSH anomalies. In a perfect model framework, where the first 200 years of each run are withheld for verification purposes while the remaining model output is used for the (seasonally-varying) analog data library, we obtain tropical Pacific SST skill found by other perfect model studies, with a Nino3.4 correlation above 0.5 for forecast leads up to 24 months. Interestingly, this perfect model predictability appears to be largely linear.
We then apply the technique to make hindcasts for the years 1982-2009 for forecast leads of 1-12 months, initializing with observed SST and SSH anomalies over that period. The model-analog hindcast skill is found to be comparable to (and often slightly better than) the corresponding CGCM hindcast skill throughout the tropical Pacific. This suggests the possibility that any CGCM with a sufficiently long control run may be used to produce skillful forecasts of monthly tropical IndoPacific SST anomalies, without the need for additional development of its data assimilation system.