Decadal Prediction Using a Recent Series of MIROC Global Climate Models

In line with the experimental design for near-term climate prediction toward the 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR5) and the Coupled Model Intercomparison Project Phase 5 (CMIP5), we perform ensembles of initialized decadal hindcast experiments using two recent versions of the Model for Interdisciplinary Research On Climate (MIROC): MIROC4h (T213L56 AGCM and 1/6-1/4 deg. 48 level OGCM) and MIROC5 (T85L40 AGCM and 0.56-1.4 deg. 50 level OGCM). We analyze sets of 10-year-long 9-ensemble hindcasts (3 members by MIROC4h and 6 members by MIROC5) with initialization every five years after 1961 and explore the predictability of decadal climate changes. The most predictable variation on decadal timescales is the global warming signal due to the favorable response of the models to external forcing. The results of these initialized hindcast experiments using MIROC5 validate our ability to enhance decadal predictability primarily through the initialization, particularly of the Pacific Decadal Oscillation (PDO) for a few years and of the Atlantic Multidecadal Oscillation (AMO) for almost a decade. The initialization has large impacts on the upper ocean temperature hindcasts over the mid- and high latitudes of the North Pacific and the high latitudes of the North Atlantic, where the PDO and AMO signals are observed to be strongest. In contribution to process and assessment studies in IPCC-AR5 and CMIP5, further analysis of our hindcast data (and near-term prediction data) using MIROC4h and MIROC5 is worthwhile. We note that the initialized hindcasts using MIROC4h have predictive skill inferior to the MIROC5 results and that at this stage, fully significant discussions may not be possible due to the small number of ensembles with limited computational resources.