NORTHERN-HEMISPHERE EXTRATROPICAL CIRCULATION ANOMALIES AND RECENT JANUARY LAND SURFACE-TEMPERATURE TRENDS

This study demonstrates that long-term January temperature trends in the Northern Hemisphere are strongly related to decadal-scale variations in extratropical mid-tropospheric circulation modes. Circulation indices derived from a rotated principal components analysis of 500-mb geopotential heights explain 72% of the January Northern Hemisphere land surface air temperature variance. An analysis of the spatial characteristics of January temperature trends from 1966 through 1985 indicates a close correspondence between the observed trends and those obtained from consideration of the phase and strength of the major modes of low-frequency mid-tropospheric variation.