Interdecadal Variation of the North Pacific Wintertime Blocking

Abstract

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.