Decadal Changes in the Atmospheric Circulation and Associated Surface Climate Variations in the Northern Hemisphere Winter

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Abstract
This study attempts to investigate decadal-scale climate changes in the mid- and high latitudes of the Northern Hemisphere in winter 1989 by using various observational data for atmospheric parameters, sea surface temperature (SST), and snow cover. Decadal-scale changes in the winter atmosphere after 1989 are characterized as follows: a dipole pattern of height anomalies between midlatitudes and polar regions with an equivalent barotropic structure, temperature changes with cooling in the polar region and warming in midlatitudes in the middle troposphere, and associated reduction of the subtropical jet stream. Statistical tests applied to the 500-hPa height field reveal that the changes in 1989 are a distinct discontinuity or shift on the decadal scale with hemispheric extent. The spatial structure is interpreted as a linear combination of three teleconnections: the North Atlantic oscillation, Pacific–North American, and Eurasian patterns, in addition to the zonally symmetric dipole. On the other... Abstract This study attempts to investigate decadal-scale climate changes in the mid- and high latitudes of the Northern Hemisphere in winter 1989 by using various observational data for atmospheric parameters, sea surface temperature (SST), and snow cover. Decadal-scale changes in the winter atmosphere after 1989 are characterized as follows: a dipole pattern of height anomalies between midlatitudes and polar regions with an equivalent barotropic structure, temperature changes with cooling in the polar region and warming in midlatitudes in the middle troposphere, and associated reduction of the subtropical jet stream. Statistical tests applied to the 500-hPa height field reveal that the changes in 1989 are a distinct discontinuity or shift on the decadal scale with hemispheric extent. The spatial structure is interpreted as a linear combination of three teleconnections: the North Atlantic oscillation, Pacific–North American, and Eurasian patterns, in addition to the zonally symmetric dipole. On the other...