Size variations and long-wave circulation within the January Northern Hemisphere circumpolar vortex: 1946-89

Abstract

In this study, digital 500-mb geopotential height data interpolated to a 5° latitude by 5° longitude grid were used to examine size variations in the January circumpolar vortex for the period 1946-89. Total January vortices were smaller than the 44-year average during the period 1946-64, after which larger than average vortices became more common. The last few years of the data record indicate that January vortices may be becoming more contracted again. These patterns of contraction and expansion are not reflective of all sectors of the vortex. Much of the vortex expansion after 1964 occurred in association with amplified troughing over the central Pacific Ocean and eastern North America/Atlantic Ocean. An inverse trend in regional vortex size within the western North American ridge indicates that more frequent occurrences of the positive Pacific/North American teleconnection pattern may be most responsible for the upward trend in total vortex size after 1964. -from Author