CHANGES IN THE ATMOSPHERIC CIRCULATION OVER THE NORTH PACIFIC-NORTH-AMERICA AREA SINCE 1950

In this study, we examine the interdecadal changes over the North Pacific area of sea level pressure and 500-mb height for the winters 1950-1988. Since most of the variance (approximately 95 %) of these two variables' asymmetric component is explained by the long-wave regime (wavenumbers 1-4), interdecadal changes in this wave regime are used for discussion. The major findings are (1) that the interdecadal changes of sea level pressure and 500-mb height were nearly barotropic and took place on the scale of the quasi-stationary long waves; (2) that the pattern of interdecadal 500-mb height change was spatially in quadrature with the 39-winter mean; and (3) that falls/rises of sea level pressure and 500-mb height in the Pacific were associated with the intensification/weakening of the lower-latitude westerlies. Version 1 of the Community Climate Model (CCM) of the National Center for Atmospheric Research (NCAR) was used to perform two numerical experiments in which the sea surface temperature (SST) anomalies in the North Pacific during the decades 1950-1959 and 1979-1988 (with respect to the 39-winter (1950-1988) mean SST) were imposed on the climatological SST of the NCAR CCM1 perpetual January control experiment. It was demonstrated that with the numerical simulations, the observed interdecadal changes of the atmospheric circulation reported in this study were apparently associated with the interdecadal changes of the tropical and extratropical North Pacific SST.