Improving Decadal Climate Predictability through the Initialization of a Coupled Model with the GECCO Oceanic Synthesis

This study aims at improving the forecast skill of climate predictions through the use of ocean synthesis data as initial conditions of a coupled climate model. For this purpose, the coupled model of the Max Planck Institute for Meteorology, consisting of the atmosphere model ECHAM5 and the ocean model MPI-OM, is initialized with oceanic synthesis fields available from the German contribution to Estimating the Circulation and Climate of the Ocean (GECCO) project. The use of an anomaly-coupling scheme during the initialization avoids the main problems with drift in the climate predictions. The coupled model is thus continuously forced to follow the density anomalies of the GECCO synthesis over the period 1952-2001. Hindcast experiments are initialized from this experiment at constant intervals. The results show improved predictive skill through the initialization on the decadal time scale for the North Atlantic sea surface temperature (SST), global mean SST, and the Atlantic Meridional Overturning Circulation. An ensemble of forecast experiments is performed subsequently over the period 2002-2011. North Atlantic SST from the forecast experiment agrees well with observation until the year 2007 and is higher than simulated without the oceanic initialization, averaged over the forecast period. Our results confirm that in decadal climate predictions, both the initial and the boundary conditions must be accounted for.