Predictability of Two Types of El Niños Assessed by ECMWF System 5 and Its Impacts on Western North American Climate

Predictability of El Nino-Southern Oscillation (ENSO) is examined using an ensemble hindcasts data obtained from the new seasonal forecasting system (system-5) of the European Centre for Medium Range Weather Forecast (ECMWF). Particular attention is paid to differences in predictive skill for two prominent types of El Nino: the canonical eastern Pacific (EP) El Nino and the central Pacific (CP) El Nino, the latter having a maximum warming around the date line. The system-5 shows a significant ability to predict ENSO with a lead time of more than half a year. However, composite analyses of each type of El Nino reveal that, compared to EP El Nino, the ability to predict CP El Nino is limited and has shorter lead time. This is because CP El Nino have relatively small amplitude, and thus they are more affected by atmospheric noise, which can limit its predictability. Finally, the sensitivity of Western North American climate to EP/CP type El Nino is also discussed during boreal winter season.