Interdecadal modulation of ENSO teleconnections

Seasonal climate anomalies over North America exhibit rather large variabil ity between years characterized by the same ENSO phase. This lack of consis tency reduces potential statistically based ENSO-related climate predictabi lity. The authors show that the North Pacific oscillation (NPO) exerts a mo dulating effect on ENSO teleconnections. Sea lever pressure (SLP) data over the North Pacific, North America, and the North Atlantic and daily rainfal l records in the contiguous United States are used to demonstrate that typi cal ENSO signals tend to be stronger and more stable during preferred phase s of the NPO. Typical El Nino patterns (e.g., low pressure over the northea stern Pacific, dry northwest, and wet southwest, etc.) are strong and consi stent only during the high phase of the NPO, which is associated with an an omalously cold northwestern Pacific. The generally reversed SLP and precipi tation patterns during La Nina winters are consistent only during the low N PO phase. Climatic anomalies tend to be weak and spatially incoherent durin g low NPO-El Nino and high NPO-La Nina winters. These results suggest that confidence in ENSO-based long-range climate forecasts for North America sho uld reflect interdecadal climatic anomalies in the North Pacific.