Consistency and the Lack Thereof in Pacific Decadal Oscillation Impacts on North American Winter Climate

Impacts of the Pacific decadal oscillation (PDO) on North American climate were initially assessed over one negative (~1943 to 1976) and one positive (1977 to ~1990) PDO regime. Release of the Twentieth Century Reanalysis and the recent occurrence of negative PDO years make it possible to study the stability of PDO teleconnections. This analysis identified consistency in broad-scale teleconnection patterns but also critical differences in the amplitude of circulation pattern, temperature, and precipitation anomalies between comparable phases of the PDO. Many of these discrepancies were apparent after controlling for long-term trends and the impact of ENSO and were associated with variability in Atlantic Ocean temperatures and in the northern annular mode. Results from this study suggest that not all of the climate variability attributed to the PDO derives solely from fluctuations in Pacific sea surface temperatures (SSTs), that the climatic impact of these SST anomalies varies over time, or that the PDO might have a “mixed” state with muted teleconnections. Any of these conclusions has substantial implications for reconstruction of the PDO and its use to understand past hydrologic or ecological changes. They suggest that evaluation of climate models on the basis of their ability to simulate teleconnection patterns of low-frequency modes of climate variability should be undertaken with the recognition that observational records may not be long enough to capture the full range of variability in teleconnection patterns.