A predictable AMO-like pattern in GFDL's fully-coupled ensemble initialization and decadal forecasting system

The decadal predictability of SST and T2m in GFDL's CMIP5 decadal hindcasts has been investigated by the Average Predictability Time (APT) analysis. By diagnosing the internal residuals between initialized hindcasts produced by the GFDL's Ensemble Coupled data Assimilation (ECDA) system and uninitialized historical forcing simulations using the the same model, internal multidecadal patterns (IMP) for SST and T2m were successfully identified. The IMP of SST is predominantly of a general inter-hemisphere dipole with warm anomalies centered in the North Atlantic subpolar gyre (SPG) region and North Pacific SPG region, and cold anomalies centered in the Antarctic Circumpolar Current (ACC) region. The IMP of T2m is predominantly of a general bi-polar seesaw. The prediction skills by the ECDA initialization, verified by independent observational datasets, reveal that the IMP of SST is predictable up to 4 (10) year lead time at 95% (90%) confidence level, and the IMP of T2m is predictable up to 2 (10) years at 95% (90%) confidence level. Further analysis demonstrated that the decadal prediction skill of the AMO-like IMP primarily originates from initialization of multidecadal variations of northward oceanic heat transports (top 1000m) in the North Atlantic. The dominant roles of oceanic internal dynamics on decadal prediction were further elucidated by fixed-forcing experiments. These results point towards the possibility of meaningful decadal climate outlook using dynamical coupled models if they are appropriately initialized by the climate observing system.