Interdecadal Variation of the North Pacific Wintertime Blocking

Using the NCEP–NCAR reanalysis data for the past four decades (1954–97), the interdecadal variation of the North Pacific winter blocking is examined. A noticeable impact on this blocking activity exerted by the Pacific decadal oscillation (PDO: deepening of the Aleutian low and amplification of the Pacific Northwest ridge) was observed. This effect included an interdecadal increasing trend of blocking days [6.5 days (40 yr)−1] and an eastward shift of blocking activity [8.7° longitude (40 yr)−1]. The possible PDO effect on the North Pacific blocking is inferred dynamically from a streamfunction budget analysis.