Limits to predictability in a coupled ocean-atmosphere model due to atmospheric noise

A coupled-ocean atmosphere model with demonstrated skill in ENSO prediction is used to examine limits to predictability due to stochastic momentum forcing from the atmosphere. Previous estimates of predictability limits in coupled models may be overly optimistic because of the absence of realistic atmospheric noise in the intermediate atmospheric model used. It is found that unavoidable error grows rapidly with a time scale of 4 or so months. It then saturates at a level around 0.5 °C for the Niño 3 region.