Significant Change of Extratropical Natural Variability Associated with Tropical ENSO Anomaly

Abstract

The natural variability over the North Pacific, where the influence of tropical El Niño?Southern Oscillation (ENSO) events is substantial, is examined to determine whether there is a large change owing to a difference in the ENSO forcing anomaly. The hindcast ensemble runs of the Seasonal Forecast Model of the National Centers for Environmental Prediction are analyzed for this assessment. Four sets of 10-member ensemble hindcasts out to 7 months with T42 horizontal resolution and another four sets with T62 resolution are examined in detail. The results consistently indicate that the natural variability, on both seasonal and monthly time scales, is significantly smaller during El Niño boreal winters than during La Niña boreal winters. The implication is that the predictability on both seasonal and monthly time scales over the North Pacific is potentially higher during El Niño winters than during La Niña winters.