Predictability of the East Asian winter monsoon indices by the coupled models of ENSEMBLES

The seasonal predictability of various East Asian winter monsoon (EAWM) indices was investigated in this study based on the retrospective forecasts of the five state-of-the-art coupled models from ENSEMBLES for a 46-year period of 1961–2006. It was found that the ENSEMBLES models predict five out of the 21 EAWM indices well, with temporal correlation coefficients ranging from 0.54 to 0.61. These five indices are defined by the averaged lower-tropospheric winds over the low latitudes (south of 30°N). Further analyses indicated that the predictability of these five indices originates from their intimate relationship with ENSO. A cross-validated prediction, which took the preceding (November) observed Niño3.4 index as a predictor, gives a prediction skill almost identical to that shown by the model. On the other hand, the models present rather low predictability for the other indices and for surface air temperature in East Asia. In addition, the models fail to reproduce the relationship between the indices of different categories, implying that they cannot capture the tropical-extratropical interaction related to EAWM variability. Together, these results suggest that reliable prediction of the EAWM indices and East Asian air temperature remains a challenge.