Strong Relations between ENSO and the Arctic Oscillation in the North American Multi-Model Ensemble

Arctic Oscillation (AO) variability impacts climate anomalies over the mid-to-high latitudes of the Northern Hemisphere. Recently, state-of-the-art climate prediction models have proved capable of skillfully predicting the AO during the winter, revealing a previously unrealized source of climate predictability. Hindcasts from the North American Multi-Model Ensemble (NMME) show that the seasonal 200-hPa AO index is skillfully predicted up to seven months in advance and that this skill, especially at longer leads, is coincident with previously unknown and strong relations (r > 0.9) with the El Niño-Southern Oscillation (ENSO). The NMME is a seasonal prediction system that comprises eight models and up to 100 members with forecasts out to 12 months. Observed ENSO-AO correlations are within the spread of the NMME member correlations, but the majority of member correlations are stronger than observed, pointing toward too high predictability in the model, or over-confidence.