INITIALIZATION AND PREDICTABILITY OF A COUPLED ENSO FORECAST MODEL

The skill of a coupled ocean-atmosphere model in predicting ENSO has r ecently been improved using a new initialization procedure in which in itial conditions are obtained from the coupled model, nudged toward ob servations of wind stress. The previous procedure involved direct inse rtion of wind stress observations, ignoring model feedback from ocean to atmosphere. The success of the new scheme is attributed to its expl icit consideration of ocean-atmosphere coupling and the associated red uction of ''initialization shock'' and random noise. The so-called spr ing predictability barrier is eliminated, suggesting that such a barri er is not intrinsic to the real climate system. Initial attempts to ge neralize the nudging procedure to include SST were nor successful; pos sible explanations are offered. In all experiments forecast skill is f ound to be much higher for the 1980s than for the 1970s and 1990s, sug gesting decadal variations in predictability.