A 50-70 YEAR CLIMATIC OSCILLATION OVER THE NORTH PACIFIC AND NORTH-AMERICA

The chronology of interdecadal climatic regime shifts is examined, usi ng instrumental data over the North Pacific, North America and the tro pical oceans, and reconstructed climate records for North America, In the North Pacific and North America, climatic regime shifts around 189 0 and in the 1920s with alternating polarities are detected, whose spa tial structure is similar to that of the previously-known climatic shi fts observed in the 1940s and 1970s. Sea-surface temperatures in the t ropical Indian Ocean-maritime continent region exhibit changes corresp onding to these four shifts. Spectra obtained by the Multi-Taper-Metho d suggest that these regime shifts are associated with 50-70 year clim ate variability over the North Pacific and North America. The leading mode of the empirical orthogonal functions of the air-temperature reco nstructed from tree-rings in North America exhibits a spatial distribu tion that is reminiscent of instrumentally observed air-temperature di fferences associated with the regime shifts. The temporal evolution of this mode is characterized by a 50-70 year oscillation in the eightee nth and nineteenth centuries. This result, combined with the results o f the analyses of the instrumental data, indicates that the 50-70 year oscillation is prevalent from the eighteenth century to the present i n North America.